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Part 3 Forestry and natural resources management.

N

Nanism--Dwarf growth.

Nannoplankton--Unattached aquatic organisms that are so small that very high magnification with the microscope is required to make them clearly visible. The magnification commonly used for them is 430 to 1,200 x.

Naphthalene--A chemical derived form coal tar and widely used as a soil fumigant, as a repellent, and in the form of moth balls to repel clothes moths.

Naphthol--[C.sub.10][H.sub.7]OH; either of the two coal tar derivatives from naphthalene, alpha-naphthol and betanaphthol. Alpha-naphthol is a pleasant- smelling solid with a melting point of 122[degrees]F (50[degrees]C). It is the standard material for impregnating tree bands used to control the codling moth. The beta-naphthol is an antiseptic.

Nappe--(1) A sheet of water flowing over a weir or dam. (2) A thin sheet of water flowing over the soil surface. (3) A thin lava flow.

Narrow Base Terrace--A terrace for controlling soil erosion. It is similar to a broad-base terrace in all respects except the width of ridge and channel: the base of a narrow terrace is usually 4 to 8 feet wide. it is subject to frequent failures and has not been widely accepted in the United States. See Broad Base Terrace, Nichol's Terrace.

National Forest System--Units of federally owned forest, range, and related lands throughout the United States and its territories dedicated to the long-term benefit for present and future generations. The National Forest System includes all national forestlands acquired through purchase, exchange, donation, or other means, the National grasslands, and land utilization projects administered under Title III of the Bankhead-Jones Farm Tenant Act and other lands, waters, or interests therein which are administered by the Forest Service or are designated for administration through the United States Department of Agriculture Forest Service as a part of the system.

National Grassland--Land, mainly grass and shrub cover, administered by the United States Department of Agriculture Forest Service as part of the National Forest System for promotion of grassland agriculture, watersheds, grazing, wildlife, and recreation.

National Park--A large area of land owned by the federal government and managed in the public interest, which is set aside for its scenic beauty, human interest, and value for recreation.

Native--(1) Designating a plant that grows naturally in a country or region; one not introduced by people. (2) Designating animals, as cattle, hogs, and horses, which, though originally introduced into a region, have lost some of their original characteristics or have gone wild: a scrub or mongrel. (3) Designating an unbranded beef hide. See Feral, Indigenous.

Native Disease--A disease caused by an indigenous organism.

Native Forage--Indigenous vegetation suitable as feed for livestock and game.

Native Species--A species that is a part of an area's original fauna or flora.

Natric Horizon--A clayey soil horizon formed in an arid environment and containing more than 15 percent exchangeable sodium content.

Natural Area--In the United States, an area permanently preserved in unmodified condition as representative of the virgin growth of a major forest or range type, primarily for the purposes of science, research, and education. Timber cutting and grazing are prohibited.

Natural Boundary--Any feature not made by people, such as a river, or a mountain ridge, which separates states, countries, or tracts of land.

Natural Control--Nature's method of maintaining a biotic balance, as in the reduction of harmful insects through the action of heat, cold, rain, drought, parasites, predators, and disease. See Integrated Pest Management.

Natural Enemy--In nature, any organism that preys or feeds upon another. A natural enemy may be introduced by people for biological control. See Myxomatosis.

Natural Habitat--The place a plant or animal naturally occupies; natural environment.

Natural Immunity--Immunity to disease, infestation, etc., that results from qualities inherent in plants, animals, or people.

Natural Land Type--A unit of land area capable of being mapped upon a combination or integration of natural characteristics, such as soils, vegetation, relief, and climate, as contrasted with types based upon use, money value, or modifications by people. See Land Type.

Natural Landscape--That aspect of the land surface resulting from the effect of relief, water, and vegetational features, produced by nature, which is essentially unmodified by people's activities. See Landscape.

Natural Levee--A low ridge, generally of sands, on the rim of the bank of a large stream, formed by the initial deposition of sediment in the natural flooding of the bottomland.

Natural Pan--A soil formed in nature that has a clay pan horizon, a fragipan horizon, or a horizon cemented by iron, aluminum, silica, calcium carbonate, gypsum, or colloidal humus. See Induced Pan.

Natural Reproduction--Renewal of plants by self-sown seeds, sprouts, rhizomes, etc.

Natural Reseeding--In range management, the restoration of depleted grazing land to permit natural revegetation by reseeding of desirable forage species.

Natural Resources--The elements of supply inherent to an area that can be used to satisfy needs of people, including air, soil, water, native vegetation, minerals, wildlife, etc.

Natural Selection--A natural process by which less-vigorous plants and animals tend to be eliminated from a population in an area without leaving enough descendants to perpetuate their traits.

Natural Selection Theory--A theory of evolution, propounded by Charles Darwin in the nineteenth century, which postulates that the distinctive characteristics of fitness can be inherited. Also called the survival of the fittest theory.

Natural System (Drainage)--The system of land drainage in which the tile lines are laid in the natural drainage depressions. Also called random system.

Natural Thinning--The death of trees in a stand as a result of competition.

Natural Water--Water ([H.sub.2]O) as it occurs in nature with extremely variable proportions of solid, liquid, and gaseous materials in solution and suspension. In common usage, the term water refers to natural water rather than to chemically pure water, deionized water, or distilled water.

Natural Watercourse--A natural stream that flows in a well-defined bed or channel. It is distinguished from an artificial watercourse, such as a dug drainage ditch or a canal.

Naturalization--The process of successful adaptation by plants and animals introduced to an area where they are not indigenous.

Naturalized Disease--A disease whose causal organism is of foreign origin but which has become established in a new habitat and has reached a state of balance with native organisms.

Naval Stores--Products, such as turpentine and rosin, obtained from the distillation of crude pine resin.

Navigable Stream--A stream that maintains an average width of 30 feet from its mouth upstream.

Neap Tide (Low Tide)--A tide having about 10 to 30 percent less range than the average, occurring about the time of quarter moons.

Neat's Foot Oil--An oil obtained by boiling the feet and bones of calves and other cattle; used as a fine lubricant, for dressing leather, and in hoof ointments.

Nebraska Potash--Salts obtained from the brines of lakes in the semiarid regions of western Nebraska that contain from 20 to 30 percent of K2O in the form of carbonate and sulfate of potassium. Not used extensively as a fertilizer.

Neck--(1) In humans and animals, the connecting link between the head and the body. (2) To tie cattle neck-to-neck (western United States). (3) (land) An elevated, narrow strip of land between two somewhat parallel streams, or water bodies; a promontory; a peninsula; an isthmus.

Necros--(Greek) Dead.

Needle Cast--A fungal disease of spruces and other conifers caused by Lophodermium filiforme, family Phacidiaceae; characterized by the lower branches of red spruce and black spruce being completely defoliated.

Needle-leaved Deciduous--Woody gymnosperms (trees or shrubs) with needle-shaped or scalelike leaves that are shed during the cold or dry season; e.g., baldcypress (Taxodium distichum).

Needle-leaved Evergreen--Woody gymnosperms with green, needle-shaped, or scalelike leaves that are retained by plants throughout the year; e.g., black spruce (Picea mariana).

Negligible Residue--The amount of a pesticide that is allowed on a food or feed crop at harvest. The trace amount that is on the crop is the result of indirect contact with the chemical.

Nematocide--Any substance used to kill parasitic worms called nematodes, abundant in many soils. Many nematodes attack and destroy plant roots. See Nematode.

Nematode--(1) Microscopic, wormlike, transparent organisms that can attack plant roots or stems to cause stunted or unhealthy growth. (2) Any of the round, threadlike, unsegmented animal worms of the phylum Nematoda, ranging in size from microscopic to 1 meter long. Nematodes may be saprophytes or parasites of plants and animals. They are responsible for important animal and plant diseases resulting in much economic loss. The animal parasites are designated as roundworm of horses and swine, and hookworm of people. Also called eelworms, roundworms, and nemas. See Root Knot.

Nematology--A branch of zoology concerned with the study of nematodes usually including their relation to plants and animals.

Nemoral--Of, or pertaining to, woods or forest, as nemoral culture.

Neoeluvium--A soil developed from the eluviation and illuviation of recent deposits, such as alluvium.

Neonicotine--Anabasine, an insecticide with acute toxicity to mammals.

Neontology--Biology; the study of existing life.

Neritic--Of or pertaining to the shallow waters adjoining the seacoast; e.g., neritic fish.

Nerve Poison--A poison that is soluble in tissue lipoids in contrast to respiratory poisons, such as cyanide gas, and physical poisons, such as oils and dusts.

Net Increment--In forestry, the addition to tree growth that represents an increase in usable timber.

Neutral Soil--A soil that is not definitely acid or alkaline; specifically, a soil with a pH between 6.6 and 7.3. See pH.

Neutron--See Atom.

Neutron Probe--A field device used for measuring soil water percentage. As neutrons emitted from the probe collide with hydrogen in water they are deflected and slowed. The slowed neutrons are deflected to the counter. The more water in the soil, the more the neutrons measured by the meter.

New Ground--Land recently cleared of shrubs, trees, grasses, forbs, stones, stumps, etc., and put under cultivation for the first time.

New Wood--In horticulture and forestry, the current year's growth.

Niche--A term used to describe the status of a plant or animal in its community, that is, its biotic, trophic, and abiotic relationships. All the components of the environment with which an organism or population interacts.

Nichol's Terrace--A once common small terrace for disposal of surplus water. It has a comparatively deep, narrow channel and a low, flat ridge with a slope that merges quite closely with the downhill side. Modern terraces are usually broad-based to allow machinery to operate over them. See Broad-base Terrace, Narrow-base Terrace.

Nicotine--A very poisonous alkaloid with an odor of pyridine from the leaves of the tobacco plant and also produced synthetically. Formerly widely used as an external parasiticide and as an insecticide.

Night Soil--Human feces and urine, an unsanitary potent manure for cropland. It is rarely used in the United States but remains in use in some other parts of the world, especially the Orient.

Nigrescent--Blackish.

Nimbus--(Latin) Rain cloud.

Nit--The egg of a louse.

Niter--Saltpeter; a mineral; KN[O.sub.3].

Nitrate--N[O.sub.3]; N combined with oxygen. The N form most used by plants. N[O.sub.3] is a gas that does not exist alone in fertilizer but is combined, as in ammonium nitrate. All nitrates are water-soluble and, when applied in surplus, move with surface waters to contaminate groundwater.

Nitrate of Ammonia--See Ammonium Nitrate.

Nitrate of Lime--See Calcium Nitrate.

Nitrate of Potash--KN[O.sub.3]; the potassium salt of nitric acid that occurs in nature only in small quantities. The pure compound contains about 46.6 percent potash ([K.sub.2]O). Used as a fertilizer or as a component in fertilizer formulations, commercial grades contain about 13 percent nitrogen and 44 percent potash.

Nitrate of Soda--

Nitre--(1) A precipitate of malic acid formed in making maple syrup. (2) Nitrate of potash (saltpeter), KN[O.sub.3], used as a fertilizer and in the manufacture of explosives. (3) Sodium nitrate, or chile saltpeter.

Nitric Acid--HN[O.sub.3]; a strong mineral acid which, combined with metals or alkalies, forms nitrates. It is now made synthetically on a large scale by passing ammonia (N[H.sub.3]) and air through a platinum gauze catalyst, whereby the ammonia oxidizes. Nitric acid is used in the production of nitrate fertilizer compounds, including nitric phosphates. Some nitric acid is used as an oxidant for carbonaceous material that causes the black color in liquid fertilizers made with commercial phosphoric acid.

Nitric Phosphate--Fertilizers made by processes involving treatment of phosphate rock with nitric acid or a mixture of nitric and/or sulfuric or phosphoric acid, or all three acids, usually followed by ammoniation.

Nitrification--The process of formation of nitrates (NO3) in the soil, from other compounds of nitrogen, by various microorganisms. Many plants, especially during their early growth, can utilize nitrogen in the form of ammonium, but all plants can metabolize nitrate nitrogen. Nitrification is very rapid in warm, moist, neutral soils. It practically ceases when the soil temperature falls below 4[degrees]C (40[degrees]F).

Nitrite--N[O.sub.2]; a partially oxidized form of nitrogen containing two atoms of oxygen for each atom of nitrogen. Soil and rumen bacteria can change nitrite-nitrogen to nitrate-nitrogen.

Nitro-Chalk--See Ammonium Nitrate-Limestone.

Nitrobacter--A genus of microorganisms occurring in productive soil that oxidize nitrites to nitrates. This genus includes two species: Nitrobacter agilis and N. winogradskyii.

Nitrobacteria--Minute, rodlike bacilli that convert nitrogen into soluble nitrates in soils.

Nitrogen--N[O.sub.2]; a gas that occurs naturally in the air and soil, where it is converted into usable forms for plant use by bacteria and other natural processes. This nutrient is a constituent of proteins and is vital to plantgrowing processes. Nitrogen can be added to the soil in any of three fertilizer forms: as urea, ammonia, or nitrates.

Nitrogen Carrier--Any of a great number of inorganic or organic compounds that contain nitrogen and can be classed as a fertilizer.

Nitrogen Cycle--The circulation of nitrogen in nature. Dead organic matter is converted to ammonium compounds during decay in the soil. These are converted to nitrates, through nitrification as a result of bacterial action, which can be utilized again by plants. Nitrosomonas oxidize ammonium ions to nitrites and Nitrobacter oxidize nitrites to nitrates.

Nitrogen Excesses--The presence of nitrogen, as nitrates or ammonium salts in soils, in excessive amounts, which results in injury to plants, as burning or stunting. The excess may occur naturally or may result from excessive applications of nitrogenous fertilizers. In tree fruits, it may cause excessive vigor resulting in reduced fruiting.

Nitrogen Oxides--Gases formed in great part from atmospheric nitrogen and oxygen when combustion takes place under conditions of high temperature and high pressure; e.g., in internal combustion engines; considered major air pollutants. Written as NOx when the oxides have not been identified, or as NO-nitric oxide and N[O.sub.2]-nitrogen dioxide.

Nitrogen Solutions--Solutions of nitrogenous fertilizer chemicals in water. Solutions are used in manufacturing liquid fertilizers and are applied to the soil either with special applicators or in irrigation water. A typical nitrogen solution is characterized by a code number, e.g., 414 (19-66-6) indicating that it contains 41.4 percent total nitrogen, 19 percent free ammonia, 66 percent ammonium nitrate, 6 percent urea, and by difference, 9 percent water.

Nitrogen-fixing Bacteria--Species of the genus Rhizobium, family Rhizobiaceae, that live symbiotically in the root nodules of leguminous plants, upon which they are dependent. They are capable of extracting nitrogen from the air and converting it to a form utilizable by the plant. Species of the genus Azotobacter and Clostridium are free-living and act independently (nonsymbiotically). Some plants that are not legumes also have a species of symbiotic bacteria. See Nodule.

Nitrogenous Materials--Materials that contain nitrogen, whether in organic or inorganic form. Some are readily available, others, even though they contain fairly high percentages of total nitrogen, such as hoof, hair, and plastic and leather scraps, are not readily available.

Nitrosamine--Any of a group of N-nitroso derivatives of secondary amines. Some nitrosamines are carcinogenic.

Nitrosobacterium--A microorganism that oxidizes nitrites (N[O.sub.3]) to nitrates (N[O.sub.3]).

Nitrosospira--A genera of two species of microorganisms that oxidize ammonia (N[H.sub.3]), to nitrate (N[O.sub.2]) very slowly: Nitrosospira antarctica and N. briensis.

Niveus--Snowy-white.

No-tillage--A system of growing crops in which the seeds are planted in the ground with little or no disturbing of the soil. Weed and pest control is accomplished through the use of chemicals. This method of farming is used to control erosion. See Conversation Tillage.

Noble Fir--Abies procera, family Pinaceae; a huge evergreen tree grown in the United States West Coast as an ornamental and for its lumber, used in general construction, boxes, pulp, and planing-mill products. Native to North America.

Nocturnal--Of the night; e.g., a nocturnal plant is one whose flowers open at night; a nocturnal animal is one which is active at night. See Diurnal.

Noise Pollution--(1) Sound that lacks agreeable quality, is noticeably loud, harsh, or discordant. (2) The addition of energy in the form of sound to the environment beyond what would naturally occur. The degree of noise pollution is measured in terms of intensity, duration, frequency of occurrence, and wavelength or pitch. (3) Sound that unreasonably interferes with the enjoyment of life or property.

Nomadism--A primitive unsettled pastoral type of existence, especially in steppe and desert regions; the life led by people who wander in search of grazing for their livestock and food for themselves.

Noncommercial Forest Land--Forestland withdrawn from its commercial use for timber because (a) it is utilized for such purposes as parks, game refuges, military reservations, or reservoir protection or (b) its poor growing conditions or inaccessibility render its commercial use unprofitable.

Nondegradable Wastes--Substances that are not changed in form and/or reduced in quantity by the biological, chemical, and physical phenomena characteristic of natural waters. Although nondegradable wastes may be diluted by receiving water, they are not reduced in total quantity. (Sometimes known as nonbiodegradable wastes.)

Nonionic Surfactants--Substances that have neither a positive nor a negative electrical charge and are compatible with most pesticides.

Nonpoint Pollution Sources--Those sources of pollution that are diffuse in both origin and in time and points of discharge, and depend heavily on weather conditions such as rainstorms or snowmelt. Pollutants can originate from natural source areas as well as areas affected by people's activities.

Nonporous Wood--Wood devoid of pores or vessels, as the conifers and a few broadleaf species.

Nonrenewable--Natural resources that once used up are gone forever.

Nonsaline-Sodic Soil--A soil that contains sufficient exchangeable sodium to interfere with the growth of most crop plants and does not contain appreciable quantities of soluble salts. The exchangeablesodium- percentage is greater than 14, and the electrical conductivity of the saturation extract is less than 4 millimhos per centimeter (at 25[degrees]C). The pH reading of the saturated soil paste is usually greater than 8.5.

Nonselective Herbicide--A herbicide that will kill any plant with which it comes in contact. See Selective Herbicide.

Nonsymbiotic Nitrogen Fixation--Fixation of nitrogen in soils by free-living microorganisms in contrast to that fixed through the agency of symbiotic organisms. See Nitrogen-fixing Bacteria.

Nontoxic--Not poisonous to plant or animal. See Toxic, Toxicity. Normal Diameter-In logging, the diameter of a tree at breast height above the root swell.

Normal Erosion--The erosion that takes place on the land surface in its natural environment undisturbed by human activity. It includes (a) rock erosion, or erosion of rocks on which there is little or no developed soil, as in stream channels and rocky mountains, and (b) normal soil erosion, or the erosion of the soil under its natural condition or native vegetative cover undisturbed by human activity.

Normal Fire Season--A forest fire season in which weather, rated fire danger, and number and distribution of fires are average.

Normal Kill--In wildlife management, the average number of animals or birds that can be killed yearly on a particular area without diminishing future productivity.

Normal Moisture Capacity--The amount of water that is normally held by a soil after the free or gravitational water has drained. See Field Capacity.

Normal Soil--A soil having a profile in equilibrium with the forces of the environment, such as native vegetation and climate. Usually developed on gently undulating upland, with good drainage, from parent material (not of extreme texture or chemical composition) in place long enough for the soil-forming process to exert their full effect.

Normal Stand--In forestry, a stand of trees fully stocked, in proper growing condition and having normal increment conforming to a yield table.

Norther--A strong wind from the north that usually brings cold, sleet, rain, or dust, especially in the Plains of the southwestern United States.

Northern Leaf Blight--A fungal disease of corn, Sudangrass, and sorghums caused by Helminthosporium turcicum, family Dematiaceae; characterized by linear or irregular, elliptical, watersoaked lesions on the leaves. The lesions turn brown, and then black. Sometimes the entire leaf dies.

Northern Rat Flea--Nosopsyllus fasciatus, family Dolichopsyllidae; a vector of diseases among people and animals, especially bubonic plague.

Northern Red Oak--Quercus rubra var. borealis, family Fagaceae; a northern variety of red oak. Lumber from the northern red oak is valuable in the making of furniture.

Northern White Cedar--Thuja occidentalis, family Pinaceae; an evergreen tree valuable for timber, posts, and as an ornamental. Native to North America.

Norway Pine--See Red Pine.

Norway Rat--Rattus norvegicus, family Muridae; a native rodent of northern Europe, now common in many civilized countries and harmful to people in various ways. Also called house rat, brown rat, wharf rat, sewer rat.

Norway Spruce--Picea abies, family Pinaceae; a hardy evergreen tree, probably the most widely grown ornamental evergreen in America; it has a large number of varieties differing in height, form, and foliage. Dwarf varieties are 1 to 2 feet high while other varieties reach a height of 150 feet.

Notch--(1) The opening in a dam or spillway for the passage of water. (2) A gap, pass, or defile between mountains (chiefly in northeastern United States). (3) An undercut; in logging, a cut in the trunk of a tree to govern direction of fall. (4) A gap cut into the ear of an animal for identification.

Notifiable Disease--(reportable) Any disease that must be reported to the government health authorities.

Novale--Land newly plowed and brought under cultivation.

Novia--An ancient Mideastern system of irrigation that uses the force of the stream or river current to turn a paddlewheel water lift.

NPK--Symbols for three primary nutrients needed by plants. N is for total nitrogen, P for available phosphorus (reported as [P.sub.2][O.sub.5]), K for water-soluble potassium (reported as [K.sub.2]O). Percentage of these nutrients in a fertilizer package is always listed in that order and is known as the fertilizer grade. See Fertilizer Grade.

Nucleus--(1) The central portion of the cell protoplast surrounded by a very thin membrane. It consists of nucleoplasm and includes within itself variously arranged chromatin, nuclear sap, and nutritive substances. It is of crucial significance in metabolism, growth, reproduction and the transmission of the determiners of hereditary characters. (2) A small colony of bees used in queen rearing or in pollination work in greenhouses. (3) A central core around which material collects or is grouped.

Nuclide--Any species of atom that exists for a measurable period of time whose nuclear structure is distinct from that of any other species. Thus each isotope of an element is a separate nuclide.

Nudation--The removal of all of the vegetation of an area.

Nuisance Birds--Starlings, sparrows, crows, redwinged blackbirds, pigeons, etc., that damage the farm, orchard, and garden crops, or become objectionable because of their roosts, or the grain they consume.

Nullah--(Hindi) Watercourse, wet or dry.

Nurse Crop--A companion crop grown to protect some other crop sown with it, as small grain is sometimes seeded with clover. The nurse crop can sometimes become competitive and harmful also.

Nut--(1) An indehiscent, one-celled and one-seeded, hard and bony fruit, as the acorn of Quercus. (2) As frequently and loosely used, a drupe with relatively thin fleshy exocarp and a large stone (pyrene), or the pyrene itself, as the walnut (Juglans) and hickory nut (Carya).

Nut Pine--(1) Any of various pines that bear edible nuts. (2) Pinus cembroides var. edulis, family Pinaceae; a hardy variation of the Mexican pinyon pine. This term may include var. monophylla.

Nut Structure--The aggregation of fine particles of soil into small subangular, blocky, or roughly rounded, masses of definite size or shape. See Soil Structure.

Nutlet--A small or diminutive nut, similar to an achene but with a harder and thicker wall.

Nutria--Myocaster coypus; an aquatic rodent valued for its pelt that is produced to a limited extent in fur framing in parts of the United States. The animal exists in the wild state, as an escape, in the marshes of Louisiana and Texas, and is trapped annually in considerable numbers. Native to South America.

Nutrient--(1) A substance that favorably affects the nutritive processes of the body; a food. (2) An element or compound in a soil that is essential for the growth of a plant. (3) In stock feeding, any feed constituent or group of feed constituents of the same general composition that aids in the support of life, as proteins, carbohydrates, fats, minerals, and vitamins.

Nutrient Cycle--The circulation of nutrient elements and compounds in and among the soil, parent rock, streams, plants, animals, and atmosphere.

Nutrient Level--(1) In soils, the amounts and proportions of plant nutrients, such as phosphorus, potassium, and nitrogen in available forms. (2) Specifically, the concentrations of any particular nutrient in the ration of animals.

Nutrient Solution--A solution in which plants may be grown, made by dissolving salts containing the essential elements for growth in water, which is used in hydroponics and in experimental work in laboratories. See Hydroponcis.

Nutriment--Nourishment; nutritious substances; food.

Nutrition--The sum of the processes by which an organism utilizes the chemical components of food through metabolism to maintain the structural and biochemical integrity of its cells, thereby ensuring its viability and reproductive potential.

Nymph--A stage in the development of some insects and related forms, such as ticks, immediately preceding the adult stage.

O

O Horizon--(Soil) Organic horizons above mineral soil. Horizons: (1) formed or forming above the mineral part; (2) dominated by fresh or partly decomposed organic material; and (3) containing more than 30 percent organic matter if the mineral fraction is more than 50 percent clay or more than 20 percent organic matter, if the mineral fraction has no clay. Proportional percentages are between these extremes. See Organic Soil Horizon.

Oak--Any deciduous, evergreen, or partly evergreen tree or shrub of the genus Quercus, family Fagaceae. Species are grown as ornamentals, as shade and lawn trees, for bark, lumber, acorns, and browse. See Oak-leaf Poisoning.

Oak Barrens--In the eastern United States, land that supports only a scrubby or sparse growth of oaks, especially scrub oak, Quercus ilicifolia, and blackjack oak, Q. marilandica; land of low agricultural value.

Oak Opening--A prairie area in an oak forest, or an area only very sparsely occupied by oaks.

Oak Skeletonizer--Bucculatrix ainsliella, family Lyonetiidae; an insect whose larvae eat oak leaves, leaving a skeletonized surface.

Oak Wilt--A very serious fungal disease of various species of oak in the North Central states of the United States, caused by Endoconi-diosphora fagacearum, known in some publications by the name of its imperfect stage, Chalara quercina, family Ophiostomataceae. It is related to the fungus causing the Dutch elm disease, and like this disease is carried by various insects that feed on the pads of fungus mycelium that are formed under the bark and project outward through cracks. It is also spread by the natural grafting of the roots of diseased and healthy trees.

Oak-leaf Poisoning--A digestive ailment, observed among cattle on the ranges of the southwestern United States; attributed to excessive ingestion of oak leaves in the spring, before grass makes its appearance. In a few instances the ailment is fatal and otherwise may cause stunted growth.

Obligate Aerobe--An organism that lives only in the presence of free oxygen.

Obligate Anaerobe--An organism that lives only in the absence of free oxygen.

Obligate Hydrophytes--Species that are found only in wetlands, e.g., cattail (Typha latifolia), as opposed to ubiquitous species that grow either in wetland or on upland, e.g., red maple (Acer rubrum).

Obligate Parasite--An organism that develops and lives only as a parasite, and is confined to a specific host.

Obligate Saprophytes--Microorganisms not related to living cells that secure their nutrients from dead organic tissue or inorganic materials.

Obligate Symbiont--An organism that is dependent on mutual relations with another for its existence.

Obnoxious Weed--(1) In dairying, any weed which, ingested by a cow, imparts an obnoxious odor or flavor to milk, cream, or butter. (2) Any serious weed pest. See Noxious Weed.

Oceanic Climate--The characteristic type of climate of land areas near oceans, which have a moderating influence on the vegetation.

Ochric Epipedon--A surface soil horizon that is too light colored or too thin to be a mollic epipedon. See Soil Taxonomy.

Octillo--Fouquieria splendens, family Fouquieriaceae; a perennial, tall, woody, cactuslike plant producing leaves for short periods whenever moisture conditions are favorable, and grown for its showy, scarlet flowers. Characteristic of certain soil conditions in the desert regions of the southwestern United States and adjacent Mexico. Native to North America. Also called coachwhip, vine cactus, candlewood, Jacob's staff, Spanish bayonet.

Ocular Estimate--Estimate by sight only. (1) In forestry, the determination of the approximate volume and quantity of standing timber without the use of measuring instruments. (2) On a range, the qualitative procedures for determining the degree of cropping of forage plants. Observations of a general reconnaissance nature are made visually: (a) by examining small random plots at the end of each grazing season.

Odor--The property of a substance, receptive to the human nose, which permits pleasant or unpleasant sensations of fragrance or smells that can be recognized.

Odor Threshold--The lowest concentration of an airborne odor that a human can detect.

Odorous House Ant--Tapinoma sessile, family Formicidae; a household ant that is a pest over much of the United States.

Oecology--See Ecology.

Ogalla Aquifer--A large aquifer extending from Nebraska to the panhandle of Texas. It contains mostly fossil water. See Aquifer; Fossil Water.

Oil Nut--See Butternut.

Oil Palm--Elaeis spp. A tree grown in many African and Asian countries for the oil that it produces. Two kinds of oil are produced; a very stable oil from the fleshy part of the fruit and palm kernel oil from inside the hard kernel. Palm oil is used as a frying fat, in margarines, and in soups and gravies. Palm kernel oil is not edible but is used in paints and varnishes.

Old Growth--A forest that has never been changed by management or harvesting. This term is misapplied by many to describe any forest that appears to be old. Individual trees in this type of forest are usually over 200 years old, and there are large standing and fallen dead trees throughout the stand.

Old Soils--In pedologic terminology, soils on flat land surfaces that have fully developed profiles but are stagnant, i.e., undergoing changes with extreme slowness. (2) Soils buried by erosion debris or volcanic detritus.

Old Wood--A shoot or branch of a woody plant that is at least one year old.

Old-field Stand--A stand of trees grown up on land once used for crops or pasture.

Old-house Borer--Hylotrupes bajulus, family Cerambycidae; an insect that infests well-seasoned wood in buildings.

Oleoresin of Pyrethrum--A product used in insecticides, obtained by treating finely ground pyrethrum with ethylene dichloride and then evaporating.

Oligohaline--Term to characterize water with salinity of 0.5 percent to 5.0 percent, due to ocean-derived salts.

Oligophagous Parasite--A parasite capable of developing upon a few closely related host species.

Oligosaprobic Zone--The area of a stream that contains the mineralized products of self-purification from organic pollution but with none of the organic pollutants remaining.

Oligotrophic--(1) Pertaining to plants that grow in areas of poor soil with respect to the nutrients. (2) Swamps or water bodies poor in humus or plant nutrients.

Oligotrophic Lakes--Deep lakes with low nutrient content and low biochemical oxygen demand (BOD). See BOD.

Oligotrophic Peat--Peat soil that is strongly acid in reaction and low or wanting in bases, such as calcium, and other mineral plant nutrients.

Oligotrophic Waters--Waters with a small supply of nutrients; hence, they support little organic production.

Omnivorous--Designating animals that feed on both flesh and plants, as people; as applied to insects, voracious, but not necessarily omnivorous. Also called amphivorous. See Carnivorous, Herbivorous.

On the Contour--See Contour Row.

One-third-atmosphere Percentage (Soil)--The moisture percentage, dry-weight basis of a soil sample that has been air-dried, screened, wetted, and brought to hydraulic equilibrium with a permeable membrane at a soil-moisture tension of 344 centimeters of water. This retentivity value closely approximates the moisture equivalent value of many soils at field capacity.

Oophagy--The eating of eggs, said of egg-eating insects.

Oospore--A resting spore produced by sexual reproduction in the downy mildews and related fungi.

Open--(1) Designating a female animal that is not pregnant. (2) Designating a body defect of cheese in which the cheese has many mechanical openings. (3) To unfold, as a flower opens. (4) Designating a rural or wilderness area in contrast to the congestion of cities and towns.

Open Flume--An uncovered passageway for irrigation water.

Open Formula Fertilizer--A fertilizer that has both the analysis and the formula or materials used in it printed on a tag or on the bag container.

Open Range--An extensive range area where grazing is unrestricted. Also, ranges that have not been fenced into management units.

Open Weather--Pleasant weather with mild temperatures and an absence of fog or severe storms., especially during the winter.

Open Woodland--A parkland type of vegetation in which trees form a closed canopy. There is very little undergrowth.

Open-ditch Drainage--Drainage of excess water from land by open ditches as opposed to tile drainage.

Opening--(1) A treeless or very sparsely timbered area in a forested region. See Oak Opening. (2) In cranberry culture, the first swelling of a terminal bud. (3) The unfolding of a flower or boll of cotton. (4) Designating the first price offered for a commodity when a market day begins.

Optimum Condition--The ideal environment, with regard to nourishment, light, temperature, etc., for an organism's growth and reproduction.

Optimum Temperature--That certain temperature at which a particular plant or animal grows satisfactorily, other conditions being favorable for growth.

Optimum Water Content--The amount of water in a soil needed by a plant for its optimum growth, varying from 40 to 60 percent the moisture-holding capacity (field capacity).

Orchard Cover Crop--Grasses, legumes, or any herbaceous plant, grown in an orchard to form a cover to reduce soil erosion, and to improve the soil through the addition of organic matter. It may also serve to use up available nitrogen so the trees will harden for winter.

Order--(1) In botanical classification of plants, a category in between class and family. (2) In soils, one of the eleven highest categories.

Organ--A distinct part of a plant or animal that carries on one or more particular functions; e.g., a leaf, wing of a bird, etc.

Organic--(1) Produced by plants and animals; of plant or animal origin. (2) More inclusively, designating chemical compounds that contain carbon.

Organic Acids--Acids containing only carbon, hydrogen, and oxygen. Among the best known are citric acid (in citrus fruits) and acetic acid (in vinegar).

Organic Fertilizers--Although not specifically defined by the leaders of organic gardening, organic fertilizers usually include only natural, organic, proteinaceous materials of plant and animal origin and exclude synthetic, organic, nonproteinaceous materials such as urea [CO[(N[H.sub.2]).sub.2]].

Organic Gardening (Farming)--A system of farming or home gardening that utilizes organic wastes and composts to the exclusion of chemical fertilizers. Advocates of the system teach that chemical fertilizers are injurious to health and that organic composts give higher yields, better quality and better taste of produce, less plant damage by insects and disease, reduction of weed menace, and stronger seeds that germinate better and produce successively stronger plants. None of these claims have so far been confirmed by reproducible (scientific) proof. Much publicity of the concept has resulted in a number of followers but it is significant that the leading followers of the concept do not depend entirely on agriculture for their livelihood. The organic gardening concept persists because of the basic truth that organic matter in soils is beneficial to agriculture. However, the sole scientific foundation for economic production of abundant and healthful foods consist of the liberal use of organic matter plus chemical fertilizers applied according to a soil test.

Organic Matter--(1) Matter found in, or produced by, living animals and plants, which contains carbon, hydrogen, oxygen, and often nitrogen and sulfur. (2) Any matter, defined as organic incorporated in or on the surface of soil. It may include undecomposed plant matter as well as that which is highly humified. Sometimes used interchangeably with humus.

Organic Phosphate Insecticide--A chemical compound used as an insecticide, such as tetraethyl pyrophosphate, ethyl metaphosphate, and tetraethyl dithio-pyrophosphate.

Organic Soil Horizon--A surface horizon of a soil formed from organic litter derived from plants and animals, and designated as the O horizons. These horizons do not include horizons formed by illuviation of organic material into mineral material, nor do they include horizons high in organic matter formed by a decomposing root mat below the surface of a mineral material, usually designated as O1 and O2.

Organic Soils--Histosols; soils having organic soil materials that extend from the surface to: (a) a depth within 10 centimeters or less of a lithic or paralithic contact, provided the thickness of the organic soil materials is more than twice that of the mineral soil above the contact; (b) any depth if the organic material rests on fragmental material and the interstices are filled with organic materials; or (c) have organic materials that have an upper boundary within 40 centimeters of the surface; (i) having a bulk density of 0.1 g/cc; (ii) the organic soil is saturated with water six months of the year. See Soil Taxonomy.

Organism--Any living individual whether plant or animal.

Organogen--Any of certain chemical elements without which organisms cannot exist: oxygen, carbon, nitrogen, phosphorus, etc.

Organoleptic--Concerning the sensory impressions, such as temperature, taste, smell, feel, sweet, sour, and salt, associated with eating and drinking.

Organophosphates--A group of nonpersistent pesticides containing phosphorus, including malathion and parathion. Malathion has low human and animal toxicity; parathion has high toxicity to humans and animals.

Oriental Rat Flea--Xenopsylla cheopis, family Pulicidae; a vector in the spread of plague from rats to people. It may also affect both domestic and wild animals.

Orophytes--Plants that grow in mountains only.

Osmunda Peat--A potting material made from the roots of fern of the genus Osmunda.

Other Forestland--Forestland incapable of producing 20 cubic feet per acre of industrial wood under natural conditions because of adverse site conditions such as infertile soils, dry climate, poor drainage, high elevation, steepness, or rockiness.

Otolith-Earstone, used by fish for its sense of balance. There is one in each plane of the semicircular canals on each side of the head, making six in all. Fishery biologists use the biggest ones to determine the age of fish.

Outcropping--A geological stratum that is exposed on the surface of the earth; as an outcropping of rock.

Outfall--The point where water is discharged from a conduit; the mouth or outlet of a drain or sewer.

Outlet Channel--In soil conservation engineering, a waterway provided to receive and carry away the runoff discharge from terrace channels and diversions. Also called terrace outlet channel.

Outwash Plain--A physical land feature of glaciofluvial origin. The plains are smooth, or where pitted are usually low in relief. The deposits are mainly sandy or coarse textured. The plains constitute a large total area of land and a large number of separate soil and land types in the glaciated region of the United States.

Ovalhead Sedge--Carex festivella, family Cyperaceae; a grasslike, herbaceous plant, found at elevations of 6,500 to 12,000 feet from New Mexico to California (United States) and north to Alberta (Canada). Its forage value is good and its fibrous roots afford protection against soil erosion.

Overbrowsing--Excessive cropping of shrubs or tree growth, usually by goats, sheep, or game animals.

Overburden--Material of any nature, consolidated or unconsolidated, that overlies a deposit of useful materials, ores, or coal, especially those deposits that are mined from the surface by open pits.

Overcutting--The cutting of a quantity of timber in excess of the mean annual growth.

Overfall--An abrupt change in stream channel elevation; the part of a dam or weir over which the water flows.

Overflow--(1) In cotton gins with a belt distributor system, the surplus cotton carried on belts to the feeders, which drops to the floor when the feeders are full. (2) The floodwater of swollen streams that spreads over bottomland.

Overflow(ed) Land--(1) Land that is subject to overflow or flooding; generally floodplains of rivers. (2) Loosely, swampland. (3) Legally, land that is covered by nonnavigable waters, but not including land covered by the normal flow of tides.

Overgraze--To graze land so heavily as to impair future forage production and to cause range deterioration through consequential damage to plants, soil, or both. Also called overstocking.

Overgrown--Designating abundant growth on a field, usually of some undesirable vegetation as weeds or brush.

Overhead Sprinkling System--A system of irrigating a small acreage by sprinkling from permanently installed overhead pipes.

Overirrigation--Application of water in excess of the need of a crop and of the water-holding capacity of the soil; it damages the plants in addition to wasting the water.

Overlay--Any transparency, containing supplemental information, superimposed over a map or a data sheet to show this information more clearly.

Overlength--In milling logs, an allowance for trim; an extra length left on a log so that it may be trimmed to an exact length.

Overseeding--(1) Seeding in a crop already established, such as seeding a forage crop in the spring on a field of winter wheat established the previous fall. (2) Using an amount of seed in excess of that necessary to assure a good stand.

Overstocked--(1) Designating a condition of a stand of trees or of a forest, in which there are more trees than normal or full stocking would require. The overstocking may be to such a degree that growth is slowed down and many trees, including dominants, are suppressed. (2) Designating a pasture, range, or grazing game area that has more animals on it than the vegetation of the area will support. See Overgraze. (3) Designating a locality in which there are too many bees.

Overstopped Trees (Suppressed)--Trees with crowns entirely below the general level of the crown cover receiving no direct light either from above or from the sides.

Overstory--That portion of trees in a forest stand that forms the upper crown cover. Also called overwood.

Oversummer--To live through the summer.

Overtopping--In river flood control, the passage of water over the top of a levee during a flood.

Overturn--(1) The mixing of the waters of a lake in the temperate zone when the summer thermal stratification ends. Most northern lakes also experience a spring overturn. (2) The period of mixing of previously stratified water masses that occurs in the spring and autumn when water temperatures in the lake are uniform.

Overuse--The utilization of key forage species on a range to such an extent that they fail to reproduce and maintain themselves over a period of time.

Overwinter--To hibernate; to live in a dormant condition through the winter months.

Oviposition--The process of laying an egg.

Ovipositor--A tubular structure in female insects used for depositing its eggs.

Ovoviviparous--Refers to animals who produce eggs that are incubated inside the body of the dam and hatch inside the body or shortly after laying. See Oviparous, Viviparous.

Oxbow--(1) A U-shaped wooden collar, part of the harness of an ox, placed on the neck of the animal with the open ends passing through the yoke. See Yoke. (2) A bend in the channel of a river resembling an oxbow. (A large river may cut across the narrow neck of a nearly circular meander and thus leave an abandoned channel, as a lake, swamp, or bayou.) Also called oxbow meander.

Oxic Horizon--A highly weathered subsurface soil horizon (endopedon) high in iron and aluminum formed in humid, tropical, old land surfaces. See Oxisols, Soil Order.

Oxidase--Oxidizing enzymes. See Enzyme.

Oxidation Pond--A person-made lake or body of water in which wastes are consumed by bacteria. An oxidation pond is the same as a sewage lagoon.

Oxisols--One of the eleven soil orders, they are soils with residual accumulations of inactive clays, free oxides, kaolin, and quartz. They occur mostly in tropical climates on old land surfaces.

Oxygen--The chemical element O; a colorless, odorless gas. The most abundant element in the earth's crust. It accounts for about 47 percent of all elemental material. It is essential in the growth of all crops and for the respiration of most forms of life.

Oxygenation--The absorption by water of elemental oxygen that has: (a) been released into the water by aquatic plants as a waste product of photosynthesis; (b) come from the atmosphere.

Oyster--The tenderloin muscle of the poultry carcass. There are two, one on each side, located just in front of the hipbones.

Oyster Shells--Shells of the marine bivalve, genus Ostrea. They are nearly pure calcium carbonate in composition; when finely ground, they make good liming material for soils and a mineral feed for livestock and poultry as a source of calcium.

Ozarks--A high plateau region that embraces a large part of southern Missouri and northern Arkansas as well as a small part of Oklahoma and Kansas (United States). The terrain is generally hilly and deeply dissected by streams. The region contains fertile bottomlands and productive soils on slopes, but the greater part is inferior agriculturally because of steep slopes and cherty soils. The productive soils of most bottomlands have recently been covered with reservoirs. The most productive soils remaining lie on relatively level ridge tops. The area is a prime retirement and recreational "paradise." It has four seasons, adequate and evenly distributed rainfall, and many reservoirs for water-related sports. The greater part of the land is primarily suited for forestry and grazing of beef and dairy cattle.

Ozone--[O.sub.3]; a pungent, colorless, toxic gas. As a product of the photochemical process, it is a major air pollutant.

P

P--Chemical symbol for phosphorus.

[P.sub.2][O.sub.5]--Phosphorus pentoxide; in current fertilizer labeling, the amount of P in fertilizer is expressed as percent of [P.sub.2][O.sub.5]. To find actual P, multiply [P.sub.2][O.sub.5] equivalent by 0.44.

P/E Ratio--Precipitation/evaporation ratio. This is an aridity index.

Pacific Coast Tick--Dermacentor occidentalis family Ixodidae; a tick that is one of the vectors of Rocky Mountain spotted fever.

Pacific Hemlock--Tsuga heterophylla, family Pinaceae; used for its lumber and as pulp, for general construction and planing-mill products. Native to the Pacific Coast from Alaska to California. Also called western hemlock (forestry name), West Coast hemlock, hemlock spruce.

Paddy Soil--The soil of a rice paddy: it is wet and subject partially to anaerobic conditions.

Paha--Low, rounded, glacial ridges of silt and clay with a loess covering in the area of Iowan glacial drift in northeastern Iowa.

Painted Hickory Borer--Megacyllene caryae, family Cerambycidae; an insect pest that infests hickory, walnut, butternut, Osage orange, and hackberry.

Paleo--A combining form meaning old, ancient, used to denote: (a) remote in the past, (b) early, primitive, archaic. Before vowels usually pale-, palae-.

Paleopedology--That branch of pedology that deals with buried soils, fossil soils, or those formed in past eras.

Palmetto Flatwoods--A kind of land, constituting extensive areas in Florida (United States), in which the ground cover or vegetation is characteristically sawplametto, although various other plants are present and the trees are mainly pines. The land is periodically very wet and very dry. The soils are leached sands commonly underlaid by organic hardpans.

Palouse--A region of about 8,000,000 acres in eastern Washington adjacent to part of Idaho and the north-central part of Oregon. It has a semiarid and subhumid climate, and undulating to hilly and dunelike topography, productive silty soil, mostly deep, but locally severely eroded and shallow over basalt rock. it was originally grassland characterized by bunch wheatgrass but is now largely in farms with wheat as the principal crop.

Palustrine--(1) Designating a swampy or boggy soil. (2) Designating a plant that grows in a swamp.

Pampas--Vast, rolling plains of grasses without trees, especially in Argentina.

Pan--(1) A compact, indurated, subsurface layer in a soil profile. See Hardpan. (2) A depression in a saltwater marsh. (3) In forestry, a wide, steel sheet used to support the end of a log in skidding. (4) A flower pot about one-half the depth of the standard flower pot; used for growing shallow-rooted plants and bulbs. Also called bulb pan, seed pan. See Fragipan.

Pancake Land--Flat, prairie land with low-lime clay soils that has a compact baked surface (eastern Texas, United States).

Pandemic--Designating a disease or organism of worldwide distribution; widely epidemic.

Panphytotic--Designating worldwide distribution of a plant disease.

Panplane--A nearly flat surface brought about by the lateral erosion of streams, which erodes the divides and causes a coalescing of all of the flood plains of a region.

Paper Birch--Betula papyrifera, family Betulaceae; a deciduous, average-sized tree grown as an ornamental in the United States for its white, paperlike bark. Native to North America. Also called canoe birch, white birch.

Paper Mulch--Heavy paper rolled out in strips to cover the soil as a mulch between rows of plants, or squares of paper with slits through which individual plants grow. The paper may be as effective as usual mulches of straw, manure, leaves, etc., in conserving moisture and preventing weed growth.

Paper Pulp--The product used in the manufacture of paper that is made by mechanical and chemical treatment of wood or other cellulose material.

Paradichlorobenzene--A white crystalline substance used in beehives to fumigate combs and to repel wax moths. It is also used as a soil fumigant.

Paraeluvium--The residual product that results from the eluviation of the weathering products of sedimentary rocks. See Eluviation.

Parasite--An organism that lives at least for a time on or in and at the expense of living animals or plants. Some diseases of people and animals are caused by parasites ordinarily classified as protozoan, helminthic, and anthropod species. There are also innumerable species of plant parasites.

Parasitic Seed Plant--A plant that obtains part or all of its sustenance from other plants; e.g., dodder and mistletoe.

Parasiticide--An agent that kills parasites.

Parent Element--The radioactive element from which a daughter element is produced by radioactive decay; e.g., radium is the parent element of radon.

Parent Material--(1) The horizon of weathered rock or partly weathered soil material from which the soil is formed. Horizon C of a soil profile. (2) The unconsolidated material from which a soil develops. See Soil Horizon.

Parent Rock--(1) The original rock from which sediments were derived to form later rocks. (2) The rock from which parent materials of soils are formed; the R horizon. See Soil Horizon.

Parental Generation--The P1 generation; the first generation in a series of crosses; usually involves homozygotes for different alleles.

Paris Green--Acetoarsenite of copper, one of the first arsenical compounds to be widely used in insect sprays as a stomach poison for the destruction of leaf-eating insects. It was almost exclusively used to control the potato beetle. Paris Green is now replaced by insecticides that biodegrade faster.

Park--(1) A natural opening of grassland or a parklike area in a forested region. (2) In the Rocky Mountain region, an enclosed valley that may be partly grassland. (3) The land enclosed in the oxbow meander of a river. (4) Land set apart to be used for public recreation.

Particle Density--The average density of the soil particles. Particle density is usually expressed in grams per cubic centimeter and is sometimes referred to as real density, grain density, or specific gravity.

Particle-size Analysis--Determination of the amounts of different particle sizes in a soil sample, usually by sedimentation, sieving, micrometry, or a combination of these methods.

Particle-size Distribution--The amount of the various soil separates, sands, silt, and clay in a soil sample, expressed as dry weight percentages.

Particulates--(1) Of or relating to particles or occurring as minute particles. (2) Finely divided solid or liquid particles in the air or in an emission. Particulates include dust, smoke, fumes, mist, spray, and fog.

Party Wall--Wall erected on a line between adjoining properties for the use of both properties.

Pass--(1) A gap, defile, or other relatively low break in a mountain range through which a road or trail may pass; an opening in a ridge forming a passageway. (2) A navigable channel, especially at a river's mouth. (3) A narrow connecting channel between two bodies of water; an inlet. (4) An opening through a barrier reef, atoll, or sand bar.

Pastoral--(1) Rural; rustic; bucolic. (2) In farming, referring to a kind of livelihood dependent almost entirely upon pasturing or herding animals, as sheep, goats, cattle, reindeer, etc.

Pastureland--(1) Land used primarily for the production of adapted domesticated forage plants to be grazed by livestock. (2) Land producing forage plants, principally introduced species, for animal consumption. Management practices usually include one more more treatments such as reseeding, renovating, mowing, liming, or fertilizing. Native pasture that because of location or soil limitation is treated like rangeland is included as pastureland.

Patana--A grassy slope with a moderate supply of moisture, resembling a savanna.

Patch--(1) A small piece of land of indefinite size used for cultivated plants, as garden patch, melon patch. (2) A relatively small island like tract named after the vegetation growing on it, as a brier patch, patch of woods, etc.

Pathobiology--The study of disease processes; biology of disease.

Pathogen--In the general sense, anything capable of causing disease, but when referred to by most veterinarians and physicians it signifies a living, microscopic, disease-producing agent such as a bacteria or virus. See Parasite.

Pathology--The science that deals with diseases and the effects that disease have on the structure and function of tissues.

Pavement Ant--Tetramorium caespitum, family Formicidae; a yellowish ant, a pest in lawns, gardens, and greenhouses.

PCBs--See Polychlorinated Biphenyls.

Pea-sick Soil--A soil that is infested with fungi that cause the root rot of peas.

Peak--(1) In turpentining, the upper point of the V-shaped streak at the top of the incision. (2) In hydrology, the maximum rate of flow recorded at a gauging station during a flood.

Peat--(1) A dark-brown or black residuum produced by the partial decomposition and disintegration of mosses, sedges, trees, and other plants that grow in wet places. (2) Fibrous, partly decayed fragments of vascular plants that retain enough structure so that the peat can be identified as originating from certain plants (e.g., sphagnum peat or sedge peat). See Histosols, Muck.

Peat Bog--A bog in which the soil or cumulose deposit is peat, a common relief and vegetational feature in the northern glaciated region of the United States from Minnesota eastward. The bog may be treeless or it may support a growth of trees, such as black spruce.

Peat Lover--A plant that grows in peat; a plant that is tolerant or adapted by nature to highly acid and other conditions found in natural peat soils.

Peat Moss--Moss plants that grow on heath bogs, such as species of Sphagnum and Polytrichum.

Peavey--In lumbering, a stout lever, 5 to 7 feet long, which is fitted with a socket, spike, and a curved steel hook that works on a bolt hinge. It is used in handling logs. Also spelled peevy.

Pecan Weevil--Curculio caryae, family Curculionidae; a weevil that infests newly formed pecans causing them to shrivel and drop. Also called hickory nut weevil.

Peccary, Collared--Pecari angulatus; a piglike mammal ranging in the wild from Texas to Paraguay, South America.

Pecky Wood--Wood having pockets of decay caused by fungi or pits or holes caused by insects and birds. It may be used for rustic interior paneling.

Ped--A unit of soil structure such as an aggregate, crumb, prism, block, or granule, formed by natural processes (in contrast with a clod, which is formed artificially by compression of a wet clay soil).

Pedistalled--Plants and stones perched on small columns (pedistals) of soil, the surrounding soil having been lost by raindrop splash erosion.

Pedogenesis--Soil formation.

Pedologist--One versed in pedology; a soil scientist.

Pedology--The science that deals with the origin, fundamental nature, and classification of soils.

Pedon--The smallest volume that can be called a soil. It has three dimensions, and it extends downward to the depth of plant roots or to the lower limit of the genetic soil horizons. Its lateral cross section is roughly hexagonal and ranges form 1 to 10 square meters, depending on the variability in the horizons.

Pedosphere--The outer soil layer of the earth in and on which organic life exists.

Pelage--The fur coat or covering of an animal, as in rabbits. See Pelt.

Pelagic--A term designating a fish or other animal that lives in the sea and far from land.

Pelophyte--A plant that grows in clayey soil.

Pelt--(1) The natural, whole skin covering, including the hair, wool, or fur of the smaller animals, such as sheep, foxes, etc. A large pelt is more often called a hide. (2) To remove the whole skin or pelt form the body of an animal.

Pemmican--A concentrated food used by American Indians and explorers that consists of powdered, dried strips of meat mixed with dried fruits and vegetables.

Peneplain--(1) A land surface worn down by erosion to a nearly flat or broadly undulating plain; the penultimate stage of old age of the land produced by the forces of erosion. (2) By extension, such a surface uplifted to form a plateau and subjected to renewed degradation and discussion.

Penetrant--Adjuvant that aids a liquid's ability to enter the pores of a surface. See Adjuvant.

Penetrometer--A device that measures the force required to push a probe rod into the soil. It can be used to measure the density or degree of compaction in a soil.

Penstock--(1) A sluice for regulating the flow of water. (2) A conduit for conducting water.

Penta--Greek for five, used in naming chemical compounds.

Pentachlorophenol--A chemical used extensively to treat fenceposts, telephone poles, and bridge planking, against fungal decay. Reports have indicated some hazard to livestock when they lick or chew on posts so treated.

Percentile Taper--The relative taper of a tree in terms of diameter at regular intervals along the stem which is expressed in percent of diameter at breast height.

Perched Water Table--(1) A body of water that has been retarded in its downward course by an impermeable or nearly impermeable bed to such an extent that it forms an upper zone of saturation overlying but separated from a lower zone. (2) An area at the bottom of a pot or bench filled with saturated growing medium.

Percolation--The downward movement of water through the soil in response to the pull of gravity.

Perennial Stream--A stream that flows throughout the year. Pergelisol-See Permafrost, Thermokarst.

Periodic Annual Increment--The growth of a stand of trees for any specified period divided by the number of years in the period.

Peripheral--Pertaining to the surface of the body of a plant, especially a tree.

Periphyton--The association of aquatic organisms attached or clinging to stems and leaves of rooted plants or other surfaces projecting above the bottom of the body of water.

Perishable--Designating any product that is liable to easy or quick destruction by rot, disease, or decomposition, such as fresh fruits, meats, and vegetables.

Perlite--A volcanic glass having numerous concentric cracks that give rise to perlitic structure. A high proportion of all perlites are rhyolitic in composition. Used in greenhouses as a synthetic soil mix. See Vermiculite.

Permafrost--Permanently frozen ground. Permafrost areas are divided into more northern areas in which permafrost is continuous, and those more southern areas in which patches of permafrost alternate with unfrozen ground. See Thermokarst.

Permafrost Table--An irregular surface that represents the upper limit of permafrost.

Permanent Dam--A dam made of concrete or masonry.

Permanent Parasites--Parasites, such as bloodsucking lice, which spend all life stages on or in the body of the host.

Permanent Soil Sterilization--Sterilization of soil by chemical treatment lasting for more than a year to suppress all undesirable vegetation on roadsides and ditch banks.

Permanent Water--A watering place that supplies water at all times throughout the year or grazing season.

Permanent Wilting Percentage--The soil moisture content at which plants remain permanently wilted unless water is added to the soil. Soil water potential at wilting can vary from -5 to -20 bars. Because of the shape of the water potential-water content drying curve, large changes in water potential at higher tensions accompany minor decreases in water content, so permanent water for plant growth is approximately 15 bars.

Permatodes--Roundworms that live in soil or water.

Permeability--The capacity of soil or rock for transmitting a fluid. Degree of permeability depends upon the size and shape of the pores, the size and shape of their interconnections, and the extent of the latter. It is measured by the rate at which a fluid of standard viscosity can move a given distance through a given interval of time. The unit of permeability is the darcy. See Darcy's Law.

Permeable--Refers to the ability of soil to be penetrated by air and water.

Perpelic--Referring to plants that grow on clay soils.

Persian Walnut--Juglans regia, family Juglandaceae; a deciduous tree grown for its edible nut, the English walnut of commerce. Native to Europe and Asia. Also called Circassian walnut, English walnut, European walnut.

Persimmon--Diospyros virginiana, family Ebenaceae; a hardy deciduous tree that bears an edible fruit and is also a bee plant. The wood has been used in the manufacture of wooden golf clubs. Also called American persimmon.

Persistent--(1) Of, or pertaining to, the presence of the calyx lobes on a ripened pome fruit, especially pear. (2) Designating fruits, flowers, leaves, etc., that remain on a plant after frost. (3) Designating a disease that is difficult to control.

Persistent Emergent--Emergent water plants that normally remain standing at least until the beginning of the next growing season; e.g., cattails (Typha spp.) or bulrushes (Scirpus spp.).

Persistent Herbicide--A herbicide that will harm susceptible crops planted in normal rotation after the harvesting of the treated crop.

Persistent Pesticide--A chemical agent used to control pests, which breaks down extremely slowly, remaining toxic to desirable species of wildlife as well as pests, under natural conditions. Some of these include DDT, chlordane, lindane, and dieldrin. Most are now forbidden or restricted in use.

Peruvian Guano--The dry excrement of marine birds obtained from islands off the coast of Peru. See Guano.

Pervious Soil--An open soil; one with large pore spaces that permits a ready flow of water through it. It is generally a sandy or gravelly soil.

Pest--Anything, such as an insect, animal, or plant that causes injury, loss or irritation to a crop, stored goods, an animal, or people.

Pest Control--The use of disinfectant, herbicide, pesticide, insecticide, management or cultural practice that controls pests. See Integrated Pest Management.

Pesticide--A substance used to control insect, plant, or animal pests. Pesticides include insecticides, herbicides, fungicides, nematocides, and rodenticides.

Pesticide Residue--Material that remains on a plant after pesticide application.

Pet--Any animal, such as a cat, dog, lamb, bird, etc., that is kept for affection and companionship.

Petra--(Greek) Rock.

Petrify--To become stone. Organic substances, such as shells, bones, and wood, embedded in sediments, become converted into stone by the gradual replacement of their tissues, particle by particle, with corresponding amounts of infiltrated mineral matter such as lime or silica.

Petrography--A branch of geology directed toward the description and systematic classification of rocks, especially igneous and metamorphic rocks by means of microscopic examination of thin sections.

Petrology--That branch of geology dealing with the origin, occurrence, structure, and history of rocks, mainly igneous and metamorphic rocks.

Petromyzontidae--The major family of the group of vertebrates comprising the lampreys and borers, eel-like, scaleless, aquatic creatures found in both fresh- and saltwater. The freshwater species, such as the brook lampreys, are harmless, nonparasitic and dwarfed, and furnish, along with their larvae, food for freshwater game fish. The sea lamprey has become established in the Great Lakes in the United States, and is a destructive parasite of salt- and freshwater fish.

pF Value--The logarithm of the height, in centimeters, of a water column necessary to produce a force equal to the energy with which moisture is held by a soil. The "p" indicates a common logarithm, and the "F" suggests force or energy.

pH--A numerical measure of acidity or hydrogen ion activity of a substance such as food or soil. The neutral point is pH 7.0. All pH values below 7.0 are acid and all above 7.0 are alkaline. The negative logarithm of the hydrogen-ion activity. The degree of acidity (or alkalinity) of a soil as determined by means of a glass, quinhydrone, or other suitable electrode or indicator at a specified moisture content or soilwater ratio, and expressed in terms of the pH scale. See Reaction.

Phase--(1) The view that a thing presents to the eye. (2) Any one of the varying aspects or stages through which a disease or process may pass. (3) In colloidal chemistry, the discontinuous portion dispersed in the dispersion medium. (4) In soil taxonomy and soil survey, soil phase terms are surface soil texture, percentage slope, stoniness, saltiness, and erosion. When appropriate these names are added to the soil series name to make a soil mapping unit.

Pheasant--Any brightly colored, gallinaceous bird of the genus Phasianus. Some species, especially the ring-necked pheasant are farm game birds, and are also raised in limited numbers for the market as a luxury meat fowl. Locally, they may be regarded as a minor pest because of the damage they do to some truck and garden crops.

Phenol-[C.sub.6][H.sub.5]OH; carbolic acid; a colorless, crystalline compound, obtained by the distillation of coal tar; widely used as a disinfectant and as an ingredient in antiseptics.

Phenol Coefficient--A figure representing the relative killing power of a disinfectant, as compared with phenol acting on the same organism for the same length of time.

Phenology--The science that deals with the time of appearance of characteristic periodic phenomena in the life cycles of natural organisms, especially in relation to climate and other environmental factors.

Phenotype--The observed character of an individual without reference to its genetic nature. Individuals of the same phenotype look alike but may not breed alike. See Genotype.

Phobia--(Greek) Fear.

Phosphate--A term commonly used to indicate a fertilizer that supplies phosphorus. A major element in fertilizers.

Phosphate Rock--Any rock or mineral that contains phosphorus in sufficient quantity to make it useful directly, or indirectly through manufacture, as fertilizers. Most phosphate rock is tricalcium phosphate, [Ca.sub.3][(P[O.sub.4]).sub.2], with various impurities. See Apatite.

Phosphates--Salts of phosphoric acid, such as those made by combining phosphoric acid with sodium, potassium, and calcium. The phosphate most commonly used in fertilizers is made by treating phosphate rock with sulfuric acid.

Phosphatide--A complex organic compound that contains choline phosphoric acid or amino-ethyl phosphoric acid. It occurs in milk, is easily destroyed by heat and oxidation, and is an important factor in the auto-oxidation of milk fat and the development of taints (off taste) in milk.

Phosphoric Acid--[H.sub.3]P[O.sub.4]; orthophosphoric acid. To be made available to plants, it is converted into soluble acid salts by processing with sulfuric acid. The amounts of available phosphorus in fertilizers are usually expressed in terms of percentage of weight of available [P.sub.2][O.sub.5].

Phosphorite--A variety of apatite which is fibrous and concretionary. See Apatite.

Phosphorized Limestone--A phosphatic limestone used as a mineral supplement in stock feeds. Fluorine is usually present in such phosphatic rocks.

Phosphorus--P; a chemical element found in soils in various mineral forms, but only small amounts are readily available to plants at any one time. It stimulates early growth and root development, and hastens grain maturity. In the water environment it enhances the growth of aquatic plants.

Phosphorus Deficiency--In soils, insufficient amounts of phosphorus in available form for optimal growth of plants, or in insufficient amounts to produce an economic or desired yield of a crop.

Photic Zone--Surface waters that are penetrated by sunlight.

Photobiotic--Living only in the presence of light, such as green plants. See Photosynthesis.

Photochemical Process--The chemical changes brought about by the radian energy of the sun acting upon various polluting substances. The products are known as photochemical smog.

Photodecomposition--The breakdown of a substance, especially a chemical compound, into simpler compounds by the action of radiant energy.

Photolysis--(1) Chemical changes brought about by the absorption of light. (2) In botany, the grouping of the chloroplasts in relation to the amount of light the plant receives.

Photoperiod--Length of the light period in a day. See Day-neutral Plant, Long-day Plant, Short-day Plant.

Photoperiodic Adaptation--The adjustment of plants in their native or artificial habitat to a definite length of daily exposure to light. See Photoperiodism.

Photoperiodicity--The response of plants or animals to the length of daily exposure to light.

Photoperiodism--The reaction of plants to periods of daily exposure to light which is generally expressed in formation of blossoms, tubers, fleshy roots, runners, etc. See Day-neutral Plant, Long-day Plant, Short-day Plant.

Photosensitization--A condition in which external parts of the body, usually the skin, become sensitive to light. This condition may occur in cattle after eating certain substances that have the ability to sensitize light-colored areas of the skin to sunlight. It can result in swellings and fluid-containing vesicles on unpigmented skins. The exudate from the vesicles forms a crust on the skin which may permanently harm the outer part of the affected skin.

Photosynthesis--Process by which green plants, using chlorophyll and the energy of sunlight, produce carbohydrates from water and carbon dioxide, and release oxygen.

Photosynthetic Rate--The time required for a plant to manufacture a given quantity of foods such as proteins, carbohydrates, and fats.

Photothermal Induction--The inducing of a plant process, particularly reproduction, by a combination of photoperiods and temperature. Also called thermophotoperiodic induction.

Phototropism--The response of a plant to the stimulus of sunlight in which the plant or its parts seem to turn to face the light. The parts of the plant receiving the direct rays grow more slowly and the plant appears to turn.

Phreatic Water--A term that originally was applied only to water that occurs in the upper part of the zone of saturation under watertable conditions; now it means all water in the zone of saturation, thus making it an exact synonym of groundwater. See Groundwater.

Phreatophyte--Any plant that sends its roots deep into the soil to the level of groundwater or to the capillary fringe above the water table. In semiarid and arid regions, these plants may be objectionable because they rob more shallow-rooted, less hardy but more desirable plants of water. However, alfalfa, a deep-rooted plant, under some conditions may be considered a phreatophyte.

Phycomycetes--Algae and fungi bearing nonsepate, branching filaments not organized into compact bodies of definite form. Containing several damping-off fungi.

Phylliform Soil Structure--A thin, leaflike layer of soil that is less distinct and thinner than platy. Where this condition is present in the C horizon, as in soils developed from thin-bedded sediments, the term laminated is used.

Phylum--The highest grouping in the taxonomy of the plant and animal kingdoms, based on assumed common ancestry.

Physical and Mechanical Pest Controls--Direct or indirect (nonchemical) measures to destroy pests outright or to make the environment unsuitable for their entry, dispersal, survival, or reproduction; e.g., steam sterilization to destroy disease organisms, flaming for the control of weeds, cold storage to control pests, metal or other material barriers to prevent pest entry. See Integrated Pest Management.

Physical Poison--Any poisonous material that exerts a physical rather than a biochemical effect, as heavy mineral oils and inert dusts.

Physical Properties--(Of soil) Different characteristics such as color, texture, consistency, depth, etc.

Physical Weathering--In soil formation, the natural disintegration of rocks and minerals by alternate heating and cooling, expansion by water freezing in crevices, corrosion by moving ice and water, splitting of rocks by roots of trees, and other physical factors, as contrasted with chemical weathering.

Physiogenic Disease--Any disease caused by unfavorable environmental factors.

Physiognomy--(1) The general, outward appearance of a plant community as determined by the life of the dominant species. (2) The physical appearance of a landscape created by a combination of land forms or relief features. (3) The external, facial features of a human or an animal.

Physiographic--Physical geography or a general description of nature or natural phenomena.

Physiographic Location--The location of a stand of trees with respect to slope aspect, slope position, and slope inclination, and the slope conformation relative to the overall terrain.

Physiologic Races--Pathogens of the same species and variety that are usually structurally indistinguishable but which differ in their physiologic behavior, particularly in their ability to parasitize varieties of a particular host.

Physiological--(1) Referring to or concerning the science of physiology or the branch of biology that deals with life processes and functions. (2) Referring to the functions of the organs of plants and animals.

Physiological Drought--Inability of a plant to obtain water from soil although the water may be present in it, as when a soil is frozen, or by reason of weak osmotic force of plant roots.

Physiological Maturity--The period of advanced age in the cycle of a tree or stand of trees when resistance to adverse influences is so low that death of a tree or net losses in volume of salable wood are likely to occur within a cutting cycle.

Physiology--The science that deals with the function of a plant or animal's body and its organs, systems, tissues, and cells.

Physioloogical Fuel Values--Units, expressed in calories, used to measure food energy in human nutrition.

Phytobezoar--Undigestible plant fibers ingested by an animal that have gathered in the rumen or stomach in the form of balls. See Bezoar, Hair Ball, Stomach Ball.

Phytoedaphon--The microflora of the soil.

Phytogenesis--History of plant evolution; the origin of vegetation.

Phytogenic Soil--See Phytomorphic Soil.

Phytohormone--See Growth Regulator.

Phytome--The vegetable substance composing a plant.

Phytometer--(1) A plant used to measure the physiological activities of the habitat. (2) A device used for measuring water transpiration of a plant.

Phytomorphic Soil--In pedology, a group of soils that includes those developed under the predominant influence of vegetation.

Phytopathogenic--Capable of causing plant disease.

Phytopathology--The science of plant disease.

Phytophagous--Feeding upon plants.

Phytophthora--A genus of fungi of the family Pythiaceae that includes a number of plant-parasitic species many of which can also live as saprophytes. At the exterior of the infected host plants the fungus sends out a downy or felty mass of hyphae, which is the downy mildew phase of the Phytophthora. Within the host plant the advancing hyphae of the fungus cause the death and decay of the invaded tissues, the rot phase of the infection. If infections occur on young stem tissues of leaves, lesions of varying sizes are produced and the blight stage results. The stem may be rotted off, and if this occurs near or just below the soil surface, the condition is called damping-off. If the conidia infect a fruit this may result in fruit rot. Storage regions underground, such as tubers, bulbs, corns, roots, may be infected by asexual spores carried into the depths of the soil by rain, as in the tuber-rot phase of late blight of potatoes. Fourteen species of genus Phytophthora are known to cause disease of about fifty economically important plants.

Phytoplankton--Plant microorganisms, such as certain algae, living unattached in the water. See Plankton, Zooplankton.

Phytotomy--Plant anatomy; dissection of vegetation.

Phytotoxin--A poisonous substance of plant origin; e.g., abrin from rosary pea, Abrus precatorius; ricin from castor bean, Ricinus communis; crotin from croton, Codiaeum variegatum; and robin from black locust, Robinia pseudoacacia. See Poison, Toxin.

Pica--An unnatural craving for unusual or excessive amounts of food usually associated with nervousness, hysteria, pregnancy, malnourishment, or anxiety created by hearing or observing dramatic events or highly competitive sports. See Geophagia, Phagomania.

Piedmont--Meaning literally at the foot of the mountain.

Piedmont Plateau Region--A physiographic division of the eastern United States; the eastward-sloping, dissected, upland plain lying between the Appalachian Mountains and the Atlantic Coastal Plain. One of the older agricultural regions of the eastern United States, it is notable in its central and southern sections for tobacco, cotton, and fruit production, red soils, and for severe soil erosion.

Pigeon--Any bird of the genus Columba. In poultry, young pigeons, or squabs, are generally dressed for the market, and old pigeons are sold alive, generally for the Jewish trade. See Squab.

Pigeon Horntail--Tremex columba, family Siricidae; a wasplike insect whose larvae bear into the trunks of diseased and dying elm, sugar maple, and other trees. Also called pigeon tremen.

Pigeon Loft--A dovecot, elevated house, or pen atop buildings for raising pigeons.

Pigeon Louse--Either of two species of lice, Columbicola columbae, or Goniocotes bidentatus, family Philopteridae. Each causes considerable annoyance both to old pigeons and to partially feathered squabs.

Pigment--Any of the natural coloring materials in the cells and tissues of plants and animals. In fruit and vegetables, the green pigment is chlorophyll; orange to red pigments are carotenoids; red to blue colors are anthocyanins; light-yellow pigments are flavoners and flavonols. In meat, the chief pigment producing the pink or red color is myoglobin.

Pigmy Forest--A small tree and shrub type of rangeland that borders other shrublands and grasslands in the western states. Also known as the pinyon-juniper vegetation type.

Pilchard Oil--The product obtained by extraction of part of the oil from the whole Pacific pilchard fish or from cannery refuse from this species of fish; it is used as a source of vitamins in animal feeds.

Pillbug--Armadillidium vulgare; not an insect but a creature closely related to the crayfish that lives in damp places, as under rotting boards. Mainly a greenhouse pest, it may eat roots of seedlings and do other damage. See Sowbug.

Pin Cherry--Prunus pennsylvanica, family Rosaceae; a deciduous tree or shrub that produces small, sour, bright red cherries on long slender stalks. Found in the United States, from the Atlantic to the Rocky Mountains and from Canada to Virginia and Tennessee, it is especially abundant on burned-over land. The foliage is sometimes lethal when browsed by livestock. Native to North America. Also called fire cherry.

Pin Oak--Quercus palustris, family Fagaceae; a hardy deciduous tree found from Massachusetts west to Michigan and Illinois and south to Arkansas. Easily transplanted, it is grown as a shade tree on city streets and in landscaping for its autumnal foliage. Its lumber is used for ties, fuel, flooring, planing-mill products, furniture, boats, etc. Native to North America.

Pine--Any cone-bearing, evergreen tree with needle-shaped leaves, of the genus Pinus, family Pinaceae. Species number about 50 in the United States and constitute valuable timber trees, a source of turpentine and rosin, ornamentals, and Christmas trees.

Pine Barrens--Land, embracing various soils, but generally sandy, and low in fertility, on which pines were the dominant growth.

Pine Engraver--Ips pini, family Scolytidae; a beetle that infests all species of pine, burrowing small circular holes into branches and trunks of trees. Native to the northern United States.

Pine Littleleaf--A fungal disease of shortleaf pines in the southern United States caused by Phytophthora cinnamomi, family Mycosphaerellaceae; characterized by short, yellow needles at the ends of branches and death of the fine roots of the tree.

Pine Meadows--A vegetational land feature of the southern Mississippi along the Gulf Coast (United States), characterized by flat topography, wetness, a scrubby growth of longleaf pine, cypress, and a ground cover of sedgy vegetation.

Pine Straw--The fallen dead needles of pine trees. The loose, open mat at the base of trees may represent the fall of several years. It gradually becomes broken and decomposed at the bottom.

Pinery--A forest area that supports a heavy growth of pines. (A localism, especially in Wisconsin and Michigan, United States.) See Pinetum.

Pinetum--A small groove or planting of pine trees kept for its aesthetic and educational value rather than as a forest.

Piney Woods--Native forest that consists predominantly of open stands of pine, especially longleaf, in contrast to deciduous and swamp forests. (Colloquial especially in the Gulf Coast region of the United States).

Pink Locust--Pink-flowering bristly locust; Robinia hispida, family Leguminosae; an excellent erosion-control shrub because of its profuse root system.

Pinon--Mexican pinyon pine that bears edible seeds.

Pioneer Plants--Herbaceous annual and seedling perennial plants that colonize bare areas as a first stage in secondary succession.

Pioneer Settlers--In the early settlement of the United States, those settlers who were the first to enter new country or virgin wilderness to establish farm homes.

Piping--(1) A series of shrill sounds made by queen bees. (2) Formation by moving water of subsurface tunnels or pipelike cavities in the soil. See Vertisols.

Piscary--The right of fishing. Common of piscary is the right of fishing in waters belonging to another person.

Piscicide--A substance used to kill fish.

Pisciculture--The production of fishing natural or artificial bodies of water under controlled conditions, such as stocking, feeding, and use of chemical fertilizers. See Aquaculture.

Piscis--(Latin) Fish.

Pit--(1) The endocarp of a drupe; the seed-stone of a fruit, as the pit of a peach or prune. (2) An excavation in soil in which vegetables, such as potatoes, carrots, and parsnips are placed and covered over for storage (seldom practiced now in the United States. (3) A place on the floor of an exchange in which traders stand when dealing in wheat, cotton, and other commodities. (4) In botany, a small hollow or depression in a cell wall. Various types are recognized in wood anatomy as blind, bordered, primordial, simple.

Pit Recharge--The draining of excess water into a large pit; the pit must permit the water to enter the water table.

Pitahaya--Lemaireocereus thurberi, family Cactaceae; a tall, treelike cactus of the arid region of Arizona, California (United States), and Mexico, which yields an edible fruit. Native to North America. Also called sweet pitahaya, aya pitaya.

Pitch--(1) The resin that occurs in the wood of conifers, as the pitch from pines. (2) A heavy, dark, viscous or solid, fusible material obtained by distillation of the tar derived from coal, wood, rosin, and petroleum oils. It consists of many organic compounds, chiefly hydrocarbons, differing according to origin. (3) The jumping action of a horse in its attempt to unseat its rider.

Pitch Pine--(1) Pinus rigida, family Pinaceae; a hardy evergreen, rugged but beautiful tree sometimes grown as an ornamental. Native to North America. (2) Any pine tree with an abundance of pitch in the wood.

Pitch Pocket--A well-defined, lens-shaped opening between or within annual growth layers of conifer wood which usually contains solid or liquid pitch.

Pitch Streak--A well-defined accumulation of pitch (resin) that is in the form of a regular streak in the wood of certain conifers.

Plains--Flat, or nearly level, extensive areas of land. Some major physiographic divisions named plains may have broken, hilly topography, and may exhibit strong relief locally. They may be classified into various kinds, as alluvial, coastal, grassland, pine, desert, high, low, etc.

Plane Survey--A survey in which the curvature of the earth is disregarded, as in ordinary field and topographic surveying.

Plankton--The small (usually less than 2 millimeters long) floating or drifting life forms in water bodies, plankton includes both plants (phytoplankton) and animals (zooplankton) that are carried passively in the water currents. Those that can swim do so to change or adjust their depth in the water, not to move from place to place. Plankton is one of the three main divisions of aquatic life, the others being nekton (the animals that swim actively and may move long distances for feeding or breeding) and the benthos (organisms that crawl about on the bottom). See Phytoplankton, Zooplankton.

Plant Analysis--Analytical procedures to determine the concentration of nutrients in plants.

Plant Association--A unit of natural vegetation essentially uniform in habitat, aspect, general appearance, ecological structure, and floristic composition; a plant community. An area may be dominated by some one of several species with minor species associated, such as a sugar maple-beech association or a bunchgrass association.

Plant Community--An assemblage of plants living together under the same environmental conditions.

Plant Cover--(1) The vegetal mantle covering the soil. (2) All plants found on a particular range regardless of their availability, palatability, toxicity, or other characteristics.

Plant Disease--A condition that affects physiologic activities of a plant so as to check normal development, lead to abnormal formations or to premature death of all or a part of a plant.

Plant Doctor--A plant pathologist; a person skilled in the treatment of plant diseases.

Plant Ecology--The science that deals with plants in relation to their environment. See Ecology.

Plant Immunity--Resistance of a plant to a pathogen so that a disease does not cause appreciable damage.

Plant Indicator--A plant that indicates soil characteristics; e.g., black walnut (Juglans nigra): high-lime, fine-textured, well-drained soil; longleaf pine (Pinus palustris): acid, coarse-textured, well-drained; basswood (Tilia americana): moderately acid, medium-textured, well-drained; blueberries (Vaccinium spp.): acid, coarse-textured, well-drained; cypress (Taxodium spp.): mildly acid, fine-textured, water-saturated. Trees that indicate areas frequently burned over are: jack pine, Pinus banksiana; lodgepole pine, Pinus contorta; pin cherry, Prunus pennsylvanica; trembling aspen, Populus tremuloides.

Plant Kingdom--One of the two great categories of living things, the other being the animal kingdom.

Plant Life--Plant organisms of any kind from lowest to highest forms, as distinguished from animal organisms.

Plant Material Centers--In the United States there are twenty-five plant material centers managed by the United States Department of Agriculture Soil Conservation Service. They receive superior grasses, legumes, forbs, shrubs, and trees. These plant materials are reproduced for distribution.

Plant Patent--A patent granted by the United States Patent Office to originators of varieties, strains, or some variation from existing varieties of asexually reproduced plants.

Plant Pathology--That branch of science that deals with the diseases of plants.

Plant Physiology--The science that deals with the response of a plant to its environment including moisture, temperature, light, and nutrients.

Plant Pigments--The colors that are in plants. Some of the pigments, chlorophylls (green), carotenes (yellow/orange), and xanthophylls (red/brown), are essential in the photosynthetic process. Other plant pigments, anthocynins (red in acid solutions and blue in alkaline solutions), anthoxanthins (yellow), and betacyanins (red), attract insects that cross pollinate flowers and are esthetically attractive. Fall colors in temperate regions are the result of these pigments.

Plant Propagation--The practice of producing new plants that may be asexual means, such as division, graftage, cuttage, layerage, etc., or by the use of seeds.

Plant Quarantine--The isolation of or restriction placed on the movement of plant materials to prevent either the plant or plant-carried insects and diseases from contaminating an agricultural area free from them. The Plant Inspection Branch of the Agricultural Research Service in the United States Department of Agriculture processes all plant materials from foreign sources.

Plant Regeneration--The development of volunteer vegetation from seed or by other natural reproductive processes from plants existing nearby.

Plant Residue--(1) Plant material, such as leaves, roots, straw, corn stover, grass, and weeds left after harvesting; any plant material remaining after any harvesting or other process. (2) Wood materials from manufacturing plants not utilized for some product; e.g., slabs, edgings, trimmings, miscuts, sawdust, shavings, veneer cores and clippings, and pulp screening.

Plant Retrogression--The process of vegetational deterioration whereby the same area becomes successively occupied by different plant communities of lower ecological order. See Plant Succession.

Plant Succession--The process of vegetational development whereby an area becomes successively occupied by different plant communities of higher ecological order. See Plant Retrogression.

Plant Variety Protection Act--This act, passed in 1970, offers legal protection to developers of new varieties of plants that reproduce sexually; that is, through seed. Developers of plants that reproduce asexually have received protection by the United States Patent Office since 1930. The law states that protection will be extended to a "novel variety" if it has these three qualifications: (a) distinctiveness: the variety must differ from all known prior varieties by one or more identifiable morphological, physiological, or other characteristics; (b) uniformity: if any variations exist in the safety, they must be describable, predictable, and commercially acceptable; (c) stability: when sexually produced, the variety must remain unchanged in its essential and distinctive characteristics to a degree expected of similarly developed varieties.

Plant-exploration Service--A very important activity of the Agricultural Research Service, United States Department of Agriculture. Plant explorers are sent all over the world to collect plants, seeds, or plant materials of desired species for breeding and development of new crops for agricultural and other uses.

Plant-tissue Test--A test, usually rapid and not precisely quantitative, using various chemical reagents that are made upon tissue and sap of growing plants to determine the adequacy of essential plant nutrients.

Plantation--(1) A large-scale agricultural unit, especially one devoted to the production of cotton or sugarcane. In pre-Civil War times in the United States, a large manorial estate on which cotton, tobacco, and other crops were produced with slave labor. (2) An artificially reforested area established by planting or by direct seeding.

Planting Easement--An easement for reshaping roadside areas, power lines, etc., and establishing, maintaining, and controlling plant growth thereon.

Plasmid--A circular piece of DNA found outside the chromosome in bacteria. Plasmids are the principal tool for inserting new genetic information into microorganisms or plants.

Plastic Limit--The moisture content at which a soil changes from a semisolid to a plastic state. A very useful test to determine trafficability. Plasticity Index--The numerical difference between the liquid limit and the plastic limit; the range of moisture content within which the soil remains plastic.

Plat--A diagram drawn to scale showing all essential data pertaining to the boundaries and subdivisions of a tract of land, as determined by a plane survey.

Plat Book--A record of recorded subdivisions of land.

Plateau--An elevated area of comparatively flat land with at least one side having a steep descent to lower land.

Platelike--Describing a soil structure that resembles a stack of plates, usually resulting from compaction caused by heavy machinery.

Platy--Designating laminated soil aggregates predominantly developed along the horizontal axes. See Structure, Soil.

Playa--A flat basin or sump area on the floor of a desert valley in the western United States. The sediments of the playa left by flooding are generally clayey, highly charged with salts, and such areas are nearly devoid of vegetation.

Pleiotropy--A situation where one gene affects more than one trait.

Plinthite--The sesquioxide-rich, humus-poor, highly weathered mixture of clay with quartz and other diluents that commonly appears as red mottles, usually in platy, polygonal, or reticulate patterns. Plinthite changes irreversibly to an ironstone hardpan or to irregular aggregates on exposure to repeated wetting and drying, especially if it is exposed also to heat from the sun. In a moist soil, plinthite can be cut with a spade, whereas ironstone cannot be cut but can be broken or shattered with a spade. Plinthite is one form of the material that has been called laterite. See Laterite.

Plot--In agricultural research, a small parcel of land, usually rectangular and of a definite size, used in comparing yields of crop varieties, testing different applications of fertilizers, comparing methods of tillage, etc.

Plow--(1) The whole implement, of various types, used to cut, break, or turn a soil layer in preparation for planting, seeding, or other agricultural practices. More specifically, the removable metal point, share and moldboard or disk, attached to a plow stock or frame. (2) Any such implement not used primarily for agricultural purposes, such as a snow plow. (3) To make a furrow or to turn over a layer of soil. (4) To cultivate; e.g., plow corn. Also spelled plough by the British.

Plow Down--To bury material lying on the surface of a field by plowing; e.g., to plow in a surface application of fertilizer, or to plow under a cover crop.

Plow Pan--A compacted layer formed in the soil immediately below plow depth. It is attributed to the sliding action and weight pressure of the plow bottom. Also called plow sole.

Plow Planting--The plowing and planting of land in a single operation. See Conservation Tillage.

Plow Under--To bury and incorporate in the soil a cover of living or dead plants by the use of the plow. See Plow Down.

Plow Up--(1) To cut a furrow slice and partly or completely to invert it. (2) To lift out of the ground unwanted plants more with the purpose of destroying than preserving. (3) To bring the surface vegetation that was turned under during a previous plowing.

Plowable--Designating land suitable, in its present condition, for plowing.

Plowable Pasture--Land ordinarily kept as pasture but that may be plowed and utilized for other crops.

Plug--(1) The mass removed by a trier or other special penetrating implement in sampling or testing an agricultural product, as a plug from a cheese, a bale of cotton, or from a watermelon. (2) An old, worn-out horse. (3) A horse with a poor conformation. (4) To repair a leak, as a dam or earth fill. (5) A block of rooted grass that is planted for the purpose of establishing a covering of grass, such as in a law.

Plutonic Rock--An igneous rock formed at great depth by magmatic crystallization or chemical alteration, such as granite.

Pluvial--Due to the action of rain; pertaining to deposits by rainwater or ephemeral streams.

Plywood--A sheet of wood, commonly 4 x 8 feet. Made by gluing together three or more thin layers of wood in such a way that the wood grain of one layer is at right angles to the one it is glued against; this increases the strength.

Pneumatophore--Stilt roots or root "knees" developed by some woody plants growing in water to facilitate respiration; e.g., baldcypress (Taxodium distichum), tupelo (Nyssa sylvatica), and mangroves (principal genera: Rhizophora, Avicennia, Conocarpus, and Laguncularia).

Poach--To catch and carry off fish or animals illegally, or by unsportsman-like methods.

Pocket--(1) A relatively small basin-depression in a land surface. (2) A short cove-type valley or hollow in a mountainous terrain. Often used in connection with water drainage and air drainage of land. See Kettle.

Pocket Gopher--A small, stout-bodied, shortlegged rodent of the family Geomyidae, which builds nests underground in fields and orchards. Its burrows may constitute a nuisance as it has been known to girdle citrus trees below the ground surface, commit minor damage to corn, and destroy roots and bulbs in gardens. Commonly found in the United States and Central America. Also called pouched rat. See Salamander.

Pocosin--A minor, natural land feature of the flat Atlantic coastal plain of the eastern United States. It is a swamp occupying shallow basins and is thus properly differentiated from creek swamps. (The term is largely restricted to the Carolinas.) Also spelled pocoson.

Pod--(1) Technically, a dry, many-seeded fruit that splits open, such as a pea pod or bean pod; a legume. (2) To form pods. (3) A flock of animals, birds, etc.

Poikilothermic--Refers to animals such as reptiles, amphibians, fish, and insects that are not able to maintain a constant body temperature; the body temperature normally varies with that of the environment.

Point of Runoff--A spray application that is just heavy enough to produce runoff from the leaves.

Point Source--Pollution that occurs from a single source.

Poison--Any substance ingested, inhaled, or developed within the body that causes or may cause damage or disturbance of function of plants, animals, or people. See Toxin.

Poison Bait--A poison mixed with wheat bran, molasses, or other attractant used to control cutworms, grasshoppers, and other insects.

Poison Hemlock--Conium maculatum, family Umbelliferae; a biennial, rank-growing herb, which is an escape and a weed in various sections of the United States. It is dangerously poisonous to people and animals, being most poisonous to stock in the spring, when the herbage is fresh. Symptoms of poisoning of cattle are loss of appetite, salivation, bloating pain, feeble but rapid pulse, and loss of muscular power. Native to Europe and Asia. Also called deadly hemlock, poison parsley, winter fern.

Poison Ivy--Toxicodendron radicans,family Anacardiaceae; a small, erect shrub or climbing vine common throughout the United States in waste places, pastures, woodlands, and along old fencerows. Apparently more dangerous to humans than to animals, contact with the plant among susceptible individuals causes severe blistering and inflammation, especially on the hands, arms, and face. Also called climbing ivy, three-leaved ivy, climath, poisonoak, poison creeper.

Poisonoak--See Pacific Poisonoak, Poison Ivy.

Poisonous--Containing poison, as a poisonous plant.

Polders--Flat tracts in the Netherlands below the level of the sea or the nearest river, such as a lake that has been drained and brought under cultivation. The surplus water is pumped out. They are protected form inundation by embankments called dikes. Half of the people in the Netherlands live below sea level. Similar to the fens of England.

Pollard--(1) A tree whose crown has been cut back to invite the production of shoots from the top. Sometimes a tree is so pruned to induce a globelike mass of foliage. (2) A hornless ox, sheep, or goat.

Pollutant--A substance, medium, or agent that causes physical impurity.

Pollution--The presence of substances in a body of water, soil, or air to impair the usefulness or render it offensive to the senses of sight, taste, or smell. Contamination may accompany pollution. In general, a public-health hazard is created, but, in some instances, only economy or esthetics are involved, as when waste salt brines contaminate surface waters or when foul odors pollute the air. Pollution is also defined as a resource out of place.

Pollution, Nonpoint Source--Cultural pollution of air or water from any physical, chemical, biological, or radiological source other than a point source. See Point Source, Pollution.

Pollution, Point Source--A discharge of pollution into air or water from a discrete source such as a pipe, ditch, well, confined animal feeding lot, floating craft, or motor vehicle. See Pollution, Nonpoint Source.

Pollution, Thermal--Discharge of heated water into surface waters at temperatures harmful to aquatic life.

Polychlor--Any of the group of the chlorinated class of insecticides, such as DDT.

Polychlorinated Biphenyls (PCBs)--A group of aromatic organic compounds each with two 6-carbon unsaturated rings, with chlorine atoms substituted on each ring and more than two such chlorine atoms per molecule of PCB. These compounds, used in the manufacture of plastics, are very stable, resist chemical and microbiological degradation, and are very toxic to people and animals.

Polyculture--The simultaneous planting of two or more crops in the same area at the same density of each as they would be planted separately in monoculture.

Polyelectrolytes--Synthetic chemicals used to speed the removal of solids from sewage. The chemicals cause the solids to flocculate or clump together more rapidly than traditional chemicals such as alum or lime.

Polygenetic Soil--Soil produced under conditions that have changed importantly with time.

Polygons, Mud Crack--Mud cracks (sun cracks, shrinkage cracks) form as sediments dry out. The cracks form polygons, which vary in number of sides and dimensions of angles between the sides. Cracks are rarely straight, and polygons may be bounded by three to eight cracks.

Polyhalite--A mineral, commonly in pink, red, or gray masses in potassium salt deposits.

Polyhedral Disease--A disease caused by a microorganism that attacks the gypsy moth and cabbage looper larvae and results in their decimation. However, people have not yet been able to spread the infection artificially for biologic control.

Polyphagia--(1) Voracious appetite. (2) An unnatural craving for many kinds of food. (3) Omnivorousness. See Bulimia, Cynorexia, Sitomania.

Polyphagous Parasite--A parasite capable of parasitizing a considerable number of host species.

Polyphosphates--Salts of polyphosphoric acids such as ammonium polyphosphates and calcium polyphosphates.

Polyphosphoric Acid--Any of a series of phosphoric acids whose molecular structure contains more than one atom of phosphorus such as pryophosphoric acid, tripolyphosphoric acid, and tetrapolyphosphoric acid. See Phosphoric Acids.

Polyploid--An organism with more than two sets of the basic or haploid number of chromosomes; e.g., triploid, tetraploid, pentaploid, hexaploid, heptaploid, octaploid.

Polysaprobic Zone--That area of a grossly polluted stream that contains the complex organic waste matter that is decomposing primarily by anaerobic processes.

Pond--A small, sometimes stagnant, body of water. It may be a natural feature, or human-made, as a farm pond made by impounding runoff water by a dam or by excavating. (In some parts of the United States, lake and pond are used for natural water bodies without any consistent distinction.)

Pond Baldcypress--Taxodium ascendens, family Pinaceae; a deciduous, coniferous tree grown for its valuable lumber used in shingles, buckets, window boxes, coffins, outdoor seats, etc., and sometimes as an ornamental. Native to the southern United States. See Baldcypress.

Pond Management--The adoption of suitable measures for the protection of ponds from siltation and for the production of fish and other wildlife.

Ponderosa Pine--Pinus ponderosa, family Pinaceae, an evergreen tree, large or small depending upon the site, and valued chiefly for its timber. Native to British Columbia, Canada, and the western United States. Also called western yellow pine, Arizona pine, bull pine, Arizona longleaf pine.

Poor Drainage--A natural condition of standing water on the surface of a saturated soil. (The term usually denotes that an excess of water is present for most desired agricultural uses of the land; for farm ponds the same drainage may be necessary.)

Poor Land--Any land that is inferior in quality for some particular use, as for agriculture. (Commonly the term is loosely used: land may be poor either because of some unfavorable relief, or because of some physical or chemical condition of the soil. Often land and soil are used interchangeably.)

Poor Man's Manure--Snow, which in some localities may be beneficial on plowed land because usually all of the water from snow goes into the soil.

Poor Outlets--Surface or subsurface drainage outlets difficult or expensive to install.

Poor Soil--A soil unsuitable for some particular plant growth because of deficiency in fertility or some unfavorable physical condition. A poor soil, however, may be valueless for one plant but quite suitable for the growth of another; e.g., a sandy, acid soil is desirable for blueberries but not suitable for alfalfa.

Poor Tilth--Poor physical condition of soil such as hard or cloddy. Poorly Graded--Refers to soil material consisting mainly of particles of nearly the same size. Because there is little difference in the size of the particles, density can be increased only slightly by compaction.

Poplar--Any tree of the genus Populus, family Salicaceae. Species are mostly quick-growing, soft-wooded trees grown as ornamentals, for pulpwood, and other wood uses. Hybrid poplars are fast-growing and make good shade trees.

Population--A group of plants, animals, or people of the same species living in a defined area.

Population Density--The number of units, persons, families, dwellings, etc., per given area. Rural density is usually expressed on a square mile basis.

Population Equivalent--A means of expressing the amount of a pollutant by equating it to the amount of pollutant from an equivalent number of persons.

Population Pressure--In wildlife, the force of increasing numbers that results in dispersion and endangers perpetuation of a species in a particular area.

Porosity--Refers to the extent of voids or openings in the soil that exist between soil particles and soil peds or clods. These pores hold water and air for absorption by plant roots. About half of soil volume which is in a good physical condition for plant growth is pore space.

Positive Ion--A cation; an ion that carries a positive charge of electricity.

Positron--A subatomic particle equal in mass and weight to the electron and having an equal but opposite charge. Positrons are emitted by some artificially radioactive isotopes.

Post Oak--Quercus stellata, family Fagaceae; a deciduous tree, whose wood is suitable for posts, ties, tight-cooperage, veneer, fuel, flooring, planing-mill products, etc. Native to central and southern United States. Also called brash oak.

Postemergent Herbicide--Applying a herbicide after the weeds begin to grow.

Potable--Referring to water that is drinkable as a result of being free of pathogens, toxic materials, unpleasant tastes, objectionable odors, color, and other undesirable physical, chemical, and biological characteristics.

Potamology--The science of streams and rivers; a branch of hydrology.

Potassium--K; the chemical element, an alkali metal, which occurs widely in minerals; e.g., in the orthoclase feldspars of granites and in salt deposits as the chlorides and sulfates. Regarded as an essential plant nutrient, potassium is present naturally in some form in all soils but in extremely variable amounts, and is likely to be in largest amounts in clay soils and in least amounts in highly silicious soils and in peats.

Potassium Chloride--KC1; the salt most commonly used as a source of potassium in fertilizers. Its commercial form is known as muriate of potash.

Potassium Fixation--The process of converting exchangeable and water-soluble potassium to slowly available potassium. Wetting and drying of clay soils tends to make available potassium less available.

Potassium Magnesium Sulfate--See Sulfate of Potash-Magnesia.

Potassium Metaphosphate--KP[O.sub.3]; a chemical containing 40 percent potash ([K.sub.2]O), which is used as a fertilizer. Commercial grades contain about 37 percent potash and 55 percent phosphoric acid.

Potassium Nitrate--KN[O.sub.3]; saltpeter, nitrate of potash; the potassium salt of nitric acid. It is manufactured by the direct reaction of potassium chloride with concentrated nitric acid to produce potassium nitrate and chlorine.

Potassium Permanganate--KMN[O.sub.4]; a powerful oxidizing compound used as a disinfectant, deodorant, and a reagent in analytical work, especially in the determination of available nitrogen in organic material. Sometimes also used as a fungicide in greenhouses.

Potassium Phosphate--Any of the various phosphates of potassium, especially potassium metaphosphate, used as fertilizers.

Potassium Phosphate Solutions--They have been used successfully as liquid fertilizers in California. They contain an average 10.6 percent [P.sub.2][O.sub.5] and 14.5 percent [K.sub.2]O. The pH in a 1 to 400 dilution is 10, indicating that the salt in solution is dipotassium phosphate ([K.sub.2]HP[O.sub.4]).

Potassium Sulfate--[K.sub.2]S[O.sub.4]; one of the carriers of potash used in the manufacture of mixed fertilizers. The salt occurs in nature, but the commercial product is manufactured by treating potassium chloride with sulfate of magnesia or sulfuric acid. The product contains about 60 percent potassium ([K.sub.2]O).

Potency--(1) The power of a medicine to produce the desired effects. (2) The ability of an embryo to develop into a viable destiny. (3) The ability of the male of any plant or animal species to fertilize the female germ cells. (4) The degree of toxicity of a chemical.

Potential Energy--Energy inherent in a mass because of its position with reference to other masses; e.g., a rock at the edge of a precipice has potential energy. Water behind a dam also has potential energy.

Potential Soil Acidity--Those hydrogen ions on the negatively charged soil particles that are not disassociated, and therefore not active in the soil solution; the amount of exchangeable hydrogen ions in a soil that can be released by cation exchange. Also called reserve soil acidity.

Pothole--(1) A hole worn into solid rock by strong currents whereby sand, gravel, and stones are spun around by the force of the current. (2) In Death Valley, a circular opening 2 to 4 feet in diameter filled with brine and lined with salty crystals. (3) A rounded, steep-sided depression resulting from downward surface solution. (4) A rounded cavity in the roof of a mine caused by a fall of rock, coal, or ore. (5) A hole in the ground from which clay for pottery has been taken. (6) A depression between sand dunes that contains water. (7) Vertical erosion in vertisols and in thermafrost. See Thermafrost, Vertisols.

Poudrette--Dried night soil mixed with charcoal powder, gypsum, lime or peat; used as a fertilizer. Used in European countries from early times, it has never been used to any extent in the United States.

Pound--(1) A unit of weight; 16 ounces avoirdupois, 12 ounces troy. The standard British unit of weight equals 7,000 grains, 1/2, 240 long ton, and 453.59 grams, the weight of 27.692 cubic inches of water at 4[degrees]C. (2) An enclosure in which stray animals are legally confined. (3) An enclosure in which groups of animals, as flocks of sheep, may be gathered for shelter, etc. (4) An enclosure used to trap wild animals.

Powder-post Beetle--Any of the beetles of the families Ptinidae, Anobiidae, Bostrichidae, or Lyctidae, which breed in old, dry wood and reduce it to powder. The greatest damage is done by species of Lyctus which confine their infestation to the seasoned sapwood of a number of hardwoods, especially oak, ash, and hickory.

Power Subsoiler--A tractor-drawn plow that has a long, narrow shank with a wedge-shaped point for deep penetration to break up stiff clay subsoils and hardpans. See Hardpan, Plowpan.

Prairie--(1) The extensive, nearly treeless and dominantly grass-covered plains of the midwestern United States that lie east of the Rocky Mountains. In a more restricted sense, the tall grasslands with blackish soils; in a more general sense the semiarid shortgrass plains as well. Also called savannah, steppe. (2) In the generally forested eastern part of the United States, any naturally treeless area that is generally dry or naturally well-drained. (3) Wet, treeless, marshy areas. (4) Prehistoric, treeless tracts that resulted from fires.

Prairie Dog--Any animal of the genus Cynomys. Species are small, stubby, burrowing rodents found in abundance on the prairies and treeless plains of the midwestern and western United States by early settlers and explorers. They are considered a nuisance by western cattlemen largely because their burrows constitute a danger to horses and their riders. They eat green crops and some insects, such as the Mormon cricket. They live in colonies or towns and through their extensive burrowing they have been a considerable factor in modifying the soil. Native to North America. Also called barking squirrel.

Prairie Sandreed--Calamovilfa longifolia, family Gramineae; a perennial, drought-enduring grass, growing from 2 to 6 feet tall, which is found from Michigan to Colorado, United States, and Alberta, Canada. Important for winter pasture and for hay though grazed but lightly in the summer. It is an important, sand-binding grass on dunes and sand hills. Native to North America. Also called prairie sandgrass.

Prairie Schooner--A covered wagon which was used by early settlers in their westward movement and occupation of the prairies and plains of the midwestern United States.

Praying Mantis--Predaceous insects of the genus Mantis, family Mantidae, which prey upon other insects and are generally beneficial to humans. They wait for their prey with front legs raised like hands in prayer and seize it when it comes within reach.

Precipitated Phosphate--A by-product from the manufacture of monocalcium phosphate that is sufficiently soluble in the soil solution to be of value as a fertilizer.

Precipitation--(1) The amount of water, hail, sleet, snow, or other moisture received from clouds. Snow is also reported in its equivalent of liquid water. Precipitation is classified by the conditions that produce the rising column of unsaturated air which is antecedent to precipitation. Convection precipitation is the result of uneven heating of the ground, which causes the air to rise and expand, vapor to condense, and precipitation to occur. This is the major type of precipitation during the summer, producing high-intensity, short-duration storms. Orographic precipitation is caused by topographic barriers that force in the moisture-laden air to rise and cool. Cyclonic precipitation is related to large low-pressure systems that require five or six days to cross the United States from the northwest or Gulf of Mexico. These systems are the major source of winter precipitation. (2) The phenomenon of a solution or suspension that is flocculated. (3) The electrostatic or other means of removal of polluting particulates from the air. See Acid Rain.

Preclimax--The stage of succession of an area that has never supported climax vegetation but is in the process of succession toward climax vegetation for a particular climate. Thus, an extremely shallow soil or soil material in the true prairie association may support preclimax blue gramagrass rather than climax bluestem, because soil development has not yet reached a stage at which it will support the latter. See Climax Vegetation.

Precommercial Thinning--Any type of thinning (cutting or otherwise killing trees in a stand) that takes place before the size or condition of the trees makes them of sufficient value to cover the costs of the activity.

Precooling--(1) Preliminary cooling of milk immediately after a milking to prevent spoilage. (2) Cooling of fruits immediately after harvesting during periods of hot weather to retard ripening and deterioration. (3) The cooling of meats after slaughter and before cutting.

Predacide--A substance that is used to kill predators.

Predatism--Intermittent parasitism, such as the attacks of mosquitoes and bedbugs upon humans.

Predator--An animal that attacks and feeds on other animals, usually smaller and weaker than itself.

Predisposition--(1) Stress or anything that renders an animal liable to an attack of disease without actually producing it. (2) The effect of one or more environmental factors that makes a plant vulnerable to infection by a pathogen.

Preemergence Application--Applying a herbicide to the soil to kill weed seeds before they germinate, or after a crop is planted but before it germinates and seedlings emerge above the soil's surface.

Preference Permit--A license valid up to ten years issued by the United States Forest Service to permit domestic livestock grazing in a National Forest. The permit is renewable annually.

Preformed Terrace--A terrace or bench constructed or sloped before a planting, as in setting out an orchard.

Preirrigation--In rice culture, the application of irrigation water prior to the usual irrigating after emergence of the plants.

Preplant Application--A treatment with a pesticide on the soil before planting or transplanting.

Preplant Soil Incorporation--A treatment with a pesticide by tilling the chemical in the soil before planting or transplanting.

Prescribed Burning--Setting fire scientifically under "safe" conditions of surface fuel, weather, and soil moisture to: (a) reduce uncontrolled fire hazards, (b) control "weed" species, (c) increase grazing, and/or (d) encourage designated forest tree species.

Preservative--(1) Any material, as salt or sugar, that delays or prevents spoilage and decay of food products, etc. (2) A substance, such as creosote, which when suitably applied to wood makes it resistant to infestation by fungi, insects, and marine borers.

Preserve--(1) In wildlife management, a game-shooting area on which game species are propagated or released. (2) A tract of land set aside for preservation of natural conditions, and protected against exploitation or any commercial use. (3) To prepare foods by cooking with some preservative so as to reduce fermentation or decomposition.

Pressure Pan--(Traffic sole, plow pan, tillage pan, traffic pan, plow sole, compacted layer) An induced subsurface soil horizon or layer having a higher bulk density and lower total porosity than the soil material directly above and below, but similar in particle size analysis and chemical properties. The pan is usually found just below the maximum depth of normal plowing and frequently restricts root development and water movement. See Plow Pan.

Prevailing Wind--The wind that comes most frequently in an area from a particular point of the compass, either seasonally or annually.

Preying Mantis--A misnomer for praying mantis occasionaly used because of the preying habit of the insect. See Praying Mantis.

Pricklypear--Any of various cacti of the genus Opuntia, family Cactaceae. Species are prostrate to treelike forms, which contain both spines and cushions or barblike hairs. Some species spread very rapidly and in some places have greatly depreciated the value of the land. With the spines and barbs burned off, the cacti have been eaten by cattle during periods of drought and scarcity of any other feed. The pearlike fruit when preserved is edible for humans. Also called devil's fig.

Primary Succession--Plant migration on newly formed soils or upon soils that have never borne vegetation, such as a sand bar in a river.

Primary Treatment (Sewage)--Removes the material that floats or will settle in sewage. It is accomplished by using screens to catch the floating objects and tanks for the heavy matter to settle in.

Primate--A member of a group of mammals including humans, monkeys, and apes.

Prime Agricultural Lands--The most productive lands for raising the common food and fiber crops; whereas unique agricultural lands are those most productive for the less common but high-value-per-acre crops such as rice, cranberries, citrus, etc. See Unique Agricultural Lands.

Primeval Forest--The forest as it existed before the advent of humans.

Primitive Area--(1) In the United States Forest Service, wilderness area. (2) In the United States National Park Servcie, an area of indeterminate size in which no commercial development nor the construction of any roads for motorized transportation is permitted.

Principal Meridian--A north and south line accurately located and used as a basis from which to construct township and section lines as used in the United States Public Land Survey.

Prism Wedge--A small hand-held prism used in forestry to estimate the basal area of a stand of trees. See Basal Area.

Prismatic Soil Structure--Blocky soil structure in which the vertical axis of a block is longer than the horizontal axis; the upper ends of the block (column) are not rounded.

Proboscis--An elongated nose, such as the snout of a hog, or of some species of insects.

Product--The herbicide as it is sold commercially. It contains not only the active ingredients but also various solvents, surfactants, carriers, and other adjuvants that are designated as inert ingredients.

Productivity Rating--The productivity of the various soils on a farm based on the expected yield of the major crop or crops with known management. The rating is a percentage based on standards developed by research and statistical records of crop yields in the region. The best soils have a productivity rating of 100. In some instances, tables have been established showing the relation of crop yield to land values, with fixed management. See Soil Survey.

Profile Leveling--A method of leveling that is used to secure the elevation of a series of points located along a line. Profile leveling is employed in laying out a terrace.

Profundal Zone--The deep- and bottom-water area beyond the depth of effective light penetration. All of the lake floor beneath the hypolimnion. See Hypolimnion.

Progenitor--An individual animal or plant that is recognized as the source of a certain type or character in its offspring.

Prognosis--Forecast as to the probable result of an attack of disease, the likelihood of recovery.

Programmed Harvest--Timber scheduled for harvest for a specified year.

Progressive--Of a disease, developing through successive stages, usually in a certain direction, whether improving or deteriorating.

Propagation--(1) Increasing the number of plants by planting seed or by vegetative means from cuttings, division, grafting, or layering. (2) Construction of drainage ditches by use of dynamite. charges are closely spaced so that detonation of one charge causes the explosion of the next charge and so on until the complete series of charges is exploded. A water-filled soil is most desirable for this method.

Proper Stocking--Stocking of a range area on the basis of its true grazing capacity in a year of adequate rainfall.

Properties--Characteristics by which a substance may be identified. Physical properties describe its state of matter, color, odor, and density; chemical properties describe its behavior in reaction with other materials; biological properties refer to any life-related characteristics such as biodegradation.

Prophylactic--Preventive or protective treatment against disease.

Prophylaxis--Prevention of disease by various measures.

Proportional Weir--(Irrigation) A weir so shaped that the flow rate of water varies directly with the water head.

Protectants--Chemicals containing heavy metals, sulfur, or organic compounds used as sprays, dusts, or dips on seeds, stems, leaves, or wounds of living plants to reduce entrance of fungi or bacteria, and on fabric or wood products to reduce decay.

Protection Forestry--The practice of forestry with the primary objectives of: (a) conserving water supplies; (b) maintaining desirable streamflow; (c) increasing groundwater storage; (d) reducing erosion and reducing sedimentation; (e) providing high-quality water and reducing pollution; (f) ameliorating adverse climatic conditions, especially wind.

Protection Strip--In white pine blister rust control, a belt or zone outside the pine stand that is included in the control unit and is freed of Ribes spp., the alternate host of blister rust.

Proteolysis--The process by which casein or some insoluble casein derivative is broken down to water-soluble compounds through the acting of organisms.

Protista--A taxonomic kingdom comprising bacteria, algae, slime molds, fungi, and protozoa. It includes all of the single-celled organisms, some of which are plantlike, some animal-like, and others different from either plants or animals.

Protopam Choloride--An antidote used for certain organo-phosphate poisons.

Protozoa--A group of one-celled organisms that generally do not contain chlorophyll, including amoebae, paramecia, flagellates, and certain spore-forming organisms; sometimes classified as one-celled animals.

Protozoacide--(1) Any chemical agent that kills protozoan parasites. (2) Any agent that is employed for the prevention, suppression, or cure of infection by protozoan parasites.

Provenance--The ultimate natural origin of a tree or a group of trees. Trees having a common center of origin.

Provenetriculus--The glandular or true stomach of birds, which is a spindle-shaped organ between the esophagus and gizzard.

Provenience--Origin; particularly the geographic origin of seed and inoculum.

Pseudo---A Greek prefix meaning false or spurious. In most scientific terms it denotes a deceptive resemblance to the substance to whose name it is prefixed, e.g., pseudocarp, false fruit.

Psittacosis--An acute or chronic viral disease of birds (domestic and wild) transmissible to humans and characterized by systemic reaction and respiratory involvement. Also called parrot fever.

Public Lands--The general public domain; lands belonging to a national government that are subject to sale or disposal and that are not reserved for any special governmental or public purpose.

Puddle--(1) Immersing bare roots of trees and shrubs in a mixture of clay soil and water during transplanting to prevent the roots from drying out. (2) Destroying the desirable soil structure if the soil is worked or cultivated when too wet.

Puffballs--Certain globose fungi, of the family Lycoperdaceae, whose ripe fruit emits clouds of spores when disturbed. The spore fruits of most species of the family are edible when young.

Pulp--(1) In paper making, the product obtained by digesting wood in a slightly alkaline or neutral sodium sulfite cooking liquor. (2) The juicy or fleshy tissue of a fruit.

Pulverize--(Soil) To reduce clods, or peds, to a fine granular state in preparation for planting seeds.

Pulverized Limestone--The product obtained by grinding either calcareous or dolomitic limestone so that all material will pass a 20-mesh sieve and half of the material, a 100-mesh sieve. It is applied to land to reduce soil acidity and to supply calcium and magnesium as a nutrient. Also called finely ground limestone. See Lime.

Punk--(1) A small, scrubby horse. (2) Partly decayed wood.

Punky--Designating a soft, weak, often spongy, wood condition caused by decay.

Pupa--(Plural, pupae) The stage between the larva and the adult in insects with complete metamorphosis, a nonfeeding and usually inactive stage.

Puparium--The hardened larval skin or protective case that encloses the living pupa.

Pupate--The change from an active, immature insect into the inactive pupal stage.

Pure Culture--(1) A crop of one species, variety, etc., grown in contrast to a customary mixture; e.g., timothy grown from a pure seeding rather than mixed with clover. (2) A bacteriological culture that contains only a single species, or one that contains those desired for a particular purpose, as a yeast culture for making vinegar.

Pure Stand--A stand in which at least 80 percent of the trees in the main crown canopy are of a single species.

Putrefaction--Decomposition of animal or vegetable matter, produced by microorganisms in the absence of oxygen.

Putrescible--Organic matter capable of putrefaction.

Pycnidium--In certain fungi, the flasklike fruiting body containing conidia.

Pyr--(Greek) Fire.

Pyrethrins--The active ingredients (pyrethrins I and II) of pyrethrum, which are derived from plants belonging to the genus Chrysanthemum, family Compositae. One of the oldest and most widely used insecticides, they control insects affecting humans, animals, crops, and households.

Pyrethrum Powder--An insecticide made from the ground flower heads of various species of chrysanthemums whose use as an insecticide is reported to have originated in the Trans-Caucasus region of Asia about 1800.

Pyrheliograph--A device for measuring the amount and intensity of the incoming radiation from the sun.

Pyrie--(1) Designating the fire factor in an environment. (2) Designating modifications of soil and vegetation caused by fire.

Pyriform--Pear-shaped.

Pyrite--Ironpyrite; Fe[S.sub.2]; the most common form of several metal pyrites, which, on roasting, yield sulfur oxides for the production of sulfuric acid.

Pyroligneous Acid--An acid liquor obtained by the destructive distillation of wood, especially of certain species of hardwoods. It is a complex mixture containing 80 to 90 percent water and many organic compounds including acetic acid and methanol. Also called pyracetic acid, wood vinegar.

Pyrology--The scientific art of protecting forests from fire.

Pyrophyte--A tree with a thick, fire-resisting bark, or one not subject to fatal damage from ordinary forest fires, such as longleaf pine.

Q

Quadrat--A small plot or sample area frequently one square meter (one milacre) in size. In ecological field studies, a unit area in which vegetation changes are recorded.

Quadrivalent--In genetics, a group of four associated homologous chromosomes.

Quagmire--Soft, miry ground, as a bog, marsh, swamp, or morass.

Quail--Any of the various species of small upland, gallinaceous game birds belonging to the genus Coturnix and allied genera of the family odontophoridae, found in many parts of the world and often erroneously called partridge. Adapted to agricultural lands, they are seldom regarded as a nuisance and are frequently propagated for game purposes. The North American bobwhite quail, Colinus virginianus, is common in the central and eastern United States. The California quail, valley quail, and mountain quail are common in the western United States.

Quaking Aspen--Populus tremuloides, family Salicaceae; a small to fairly tall, short-lived, deciduous tree. It is the most widely distributed tree in North America. It occurs from New Jersey to Alaska. It grows in dense stands following logging or burning of forestlands. Its wood is now valued chiefly as a source of pulp for paper making, and it furnishes browse for sheep, goats, and deer, and food for beaver. Native to North America.

Qualitative Traits--Traits having a sharp distinction between phenotypes, and which are usually controlled by only a few genes; e.g., various coat colors and the horned trait in domestic animals.

Quantitative Traits--Traits that do not have a sharp distinction between phenotypes, and usually require some kind of measuring tools to make the distinctions. These traits are normally controlled by many pairs of genes; e.g., growth rate, milk production, and carcass quality. See Genotype, Phenotype.

Quarantine--(1) A regulation under police power for the exclusion or isolation of animal and plant pests or diseases and insects: (a) the isolation of an animal sick with a contagious disease; (b) a place where the sick are detained away form other animals until the danger of spread of a contagious disease has disappeared. In its wider application, the quarantine may be enforced against an individual animal, against all the animals, or all the animals of the same species, in a township, county, or state, and against those in a foreign country. (2) Prohibition to prevent the introduction or spread of any dangerous insects or plant diseases.

Quarter--(1) In slaughtering for meat, one half of the side of beef, as the forequarter or hindquarter. (2) Pertaining to a horseshoe, the branch between the last nail hole and the heel. (3) A unit of weight: (a) one-quarter cwt. (25 pounds) (avoirdupos); (b) eight bushels, formerly one-quarter ton (especially of grain). (4) A quarter section of land, or 160 acres. (5) A section of the bovine udder. Quarter Section--According to the survey of public lands by the general Land Office (United States), one of four parts of a section of land, generally 160 acres. The square section of land was divided into four equal parts by a north-south and east-west line, and in a legal land description the quarters were designated by the points of the compass as NE, NW, SE, and SW.

Quartz--Si[O.sub.2]; a mineral that is a crystalline form of silica. It is the most common mineral component of sand soils, especially in humid regions. The earth contains about 47 percent oxygen and 28 percent silica.

Quick Lime--See Lime.

Quick Tests--Certain standard chemical tests devised for the very rapid determination of the amounts of nutrient elements in a soil. When properly performed and interpreted such tests are useful in making recommendations for fertilizers and lime.

Quick-Growing--Designating a plant in a particular climatic region that matures in a comparatively short period; e.g., buckwheat and aspen are quick-growing among crops and trees in a cool climate.

Quicksand--Any loose fine sand that is mobile or semifluid when supersaturated with water. It is encountered in excavations, especially in localities where soils are derived from lacustrine sediments or river alluvium. Also called running sand.

Quinine--An alkaloid obtained from the bark of the tropical tree Cinchona officinalis. It is a white crystalline powder that is odorless with a very bitter taste. Its principal use is in medicine where it is specific for all forms of malaria. Also used for its analgesic, oxytocic, antipyretic, and scierosing properties. Quinine can be made synthetically.

R

R Horizon--Underlying consolidated bedrock, such as granite, sandstone, or limestone. See Soil Horizon.

R Layer--In soil profile description, the rock on which the soil rests. See Soil Horizon.

Rabbit--Any of certain small mammals of the family Leporidae. Hare and rabbit are often used interchangeably. However the biologist classifies the rabbit as having shorter and smaller legs and ears, and giving birth to naked and helpless young with eyes closed, while the newborn hare has fur and is quite capable of caring for itself.

Rabbit Control--See Myxomatosis.

Rabbit Pox--An acute eruptive disease of laboratory rabbits, caused by a virus related to vacinia virus.

Rabbit-proof Fence--A fence of special design which is placed around cultivated fields in New South Wales, Victoria, and Western Australia to keep out rabbits which have overrun the country and have become a very serious pest.

Rabies--An infectious disease caused by a filterable virus which is communicable by means of a bite in which saliva containing the virus enters the wound. It occurs most frequently in dogs, but many other animals and people are quite susceptible. Also called hydrophobia or canine madness.

Raccoon--Procyon lotor, family Procyonidae; a nocturnal mammal, which is gray, with black and white facial markings. It eats and does some damage to corn especially when the kernels are well-developed but soft.

Race--(1) A group of individual plants which have certain common characteristics because of ancestry. It is generally considered a subdivision of a species; frequently used in plant breeding. (2) Pathogens of the same species and variety which are structurally indistinguishable but which differ in their physiological behavior, especially in their ability to parasitize varieties of a given host. (3) The channel that leads water to or from a waterwheel, the former is the head race and the latter the tail race. (4) A narrow passage or fenced land in a sheep yard for branding, dipping, etc. (5) An elongated white mark on the face of a horse or dog.

Rack--(1) The gait of a horse in which only one foot touches the ground at any one time, producing a four-beat gait. (2) A frame attached to a truck or wagon for the transportation of hay, tobacco, etc. (3) The rib portion of a sheep carcass. (4) A framework for holding feed for cattle, swine, sheep, etc., with upright partitions so that the animal can insert its head between the partitions and have access to the feed. (5) A frame placed in a stream to prevent the passage of fish. (6) A frame placed at the entrance to a sump pump to remove debris that would clog the pump.

Radical--A group of different elements acting as a single unit in a chemical reaction; normally incapable of separate existence. A radical may be negatively charged, positively charged, or without a charge.

Radioacative Tracers--Small quantities of radioactive isotope mixed with larger amounts of the corresponding stable isotope to be used as labels. Since the stable and radioactive isotope act chemically and biologically in the same manner, as the radioactive one is readily detected.

Radioactive Element--An element capable of changing spontaneously into another element by the emission of charged particles from the nuclei of its atoms. For some elements, e.g., uranium, all known isotopes are radioactive; for others, e.g., potassium, only one of the several isotopes is radioactive. Radioactive isotopes of most elements can be prepared artificially, but only a few elements are naturally radioactive.

Radioactive Soil--A soil which possesses a minute degree of radioactivity. Radioactive phosphorus and other plant nutrients are sometimes added to the soil in research work to discover more facts about their functions in plant growth.

Radioactivity--The nuclear energy released when the nucleus of an atom disintegrates.

Radiocarbon Dating--The determination of the age of organic remains by measuring its radioactivity caused by the presence of C14 which has a half-life of 5,568 years and maintains a constant rate of disintegration after the death of an organism.

Radius Cruising--The distance between locations at which an individual animal is found at various hours of the day, at various seasons, or at times during various years.

Ragged--Of the fur or hair of animals, shaggy, rough, and hanging in tufts.

Rain--Precipitation in the form of water condensed from the atmosphere which falls in drops.

Rain Belt--A region of heavy or above-average rainfall.

Rain Forest--A low-altitude, closed, evergreen (usually broad-leaf) forest, in equatorial regions where annual rainfall exceeds 80 inches with no or very short dry seasons and where the temperature is high and constant and does not approach freezing at any time.

Rain Shadow--Refers to an area in which little or no rain falls because it is located to the leeward or dry side of mountains which on the opposite side are exposed to moisture-laden winds.

Rainbow Trout--A highly valued game fish, Salmo gairdnerii, that inhabits cool, clear streams and lakes. The fish are greenish in the upper body, white on the belly and have a pink or red stripe down the side. They are grown commercially for stocking lakes and streams.

Raindrop Erosion--Soil splash resulting from the impact of raindrops on bare supersaturated soil. The result is surface sealing and sheet erosion.

Rainfall--The amount of precipitation, expressed in the form of water but including snow, sleet, and hail which falls in a given time. In the United States, it is usually measured in inches of water.

Rainfall Distribution--The distribution of annual rainfall over the different seasons or months.

Rainfall Intensity--The rate at which rain is falling at any given instant, usually expressed in inches per hour.

Rainfall Interception--The amount of rainfall retained by leaves, branches, trunks, and surface vegetation, both living and dead, which never reaches the soil.

Rainfall Penetration--The depth below the surface of the soil reached by a given quantity of rainfall.

Rainmaker--(1) A rain simulator used for applying water in drops upon a research plot surface. (2) An individual who claims to be able to increase the rainfall of an area.

Rainstorm--A storm accompanied by rain.

Rainwater--Water that falls from the atmosphere in the form of rain, at times being caught and directed into cisterns for further use.

Rainy Season--In the tropics, the annual season of heavy or more-than-normal rainfall as contrasted to the dry season of little or no rainfall.

Raise--To grow or produce, as to raise corn or cattle.

Rammed Earth Wall--An earthen wall made by packing moist clay between heavy plank forms. Some type of protective cover of the earth wall is constructed to decrease raindrop splash erosion.

Ranch Cattle--Any of the several crossbred varieties of cattle raised as beef animals; e.g., the Santa Gertrudis; the Beefmaster, a three-way cross of Brahman (Zebu), Herefore, and Shorthorn; and the Brangus, an animal which is about 37 percent Brahman (Zebu) and 63 percent Aberdeen Angus. Others include the Braford, a cross between the Brahman (Zebu) and the Hereford; and the Charbray, an animal 12.5 to 25 percent Brahman, the main strain being Charolais. The purpose of this crossbreeding has been to produce beef animals better adapted to tropical climates and more resistant to tick fever.

Random Sample--A sample taken without bias from an area or from a population in which every part has an equal chance of being taken, in contrast to systematic sampling.

Random Searching--The hypothesis that postulates that an organism obtains food, suitable niches, and mates by entirely unorganized search, in contrast to systematic searching.

Rang Utilization--(1) For a single plant or species, the degree to which the foliage or herbage has been removed in percentage of the current growth within reach of livestock. (2) For an entire range, the relative amount eaten.

Range--(1) Uncultivated land, including forest land, which produces forage suitable for livestock grazing. (2) Specifically, a unit of grazing land used by an integral herd of livestock. (3) Ecologically, the geographic area of natural occurrence of certain plants or animals. (4) In the United States land survey, a tier of townships, according to number east or west of a principal meridian line. See Township. (5) The difference between extremes.

Range Allotment--A specific range area to which certain livestock of a permittee or group of permittees are assigned. Also called grazing allotment.

Range Appraisal--A definite, written, detailed opinion by a qualified appraiser of the value of range land. Among the considerations involved are its grazing capacity, accessibility, facilities for handling livestock, availability of feed sources, and income-producing ability.

Range Caterpillar--Hemileuca oliviae, family Saturniidae; a range pest on wild grasses in the southwestern United States, which sometimes infests corn and other cultivated plants. Its larvae are covered with coarse, poisonous spines.

Range Condition--(1) The state of health or productivity of both soil and forage of a given range in terms of what it could or should be under a normal climate and under the best practicable management. (2) An animal that is in a sufficient state of health or condition to be kept on the range.

Range Count--A census made on a range of the animals using a grazing area as contrasted to feedlot, corral, driveway, or other similar counts.

Range Crane Fly--Tipula simplex, family Tipulidae; an insect whose dark, leathery maggots bore into and destroy plant roots. It is sometimes destructive on the ranges of southwestern United States.

Range Ecology--The specialized branch of ecology which deals with vegetational response to environmental factors on rangeland, especially with the effects of grazing.

Range Fire--On rangeland, any fire which is not being used as a tool in range management.

Range Indicator--Any plant community portraying the condition of its environment which can be used as an indicator for the condition of a range.

Range Paralysis--See Fowl Paralysis.

Range Plant--Any herbaceous or shrubby plant which grows on a range.

Range Plant Cover--The ground vegetation composed of all herbaceous and shrubby plants which are within easy reach of livestock on a range area regardless of whether or not they constitute forage.

Range Readiness--The stage of growth of the important palatable plants on the range and the condition of soil which permits grazing without undue compacting of the soil or endangering the maintenance of the plants.

Range Renovation--Improving rangeland by discing or other mechanical means, chemical treatment, or reseeding.

Range Site--An area of land having a combination of edaphic, climatic, topographic, and natural biotic factors that is significantly different from adjacent areas. Various sites are significantly different in their potential forage production and/or different in management requirements for proper land use.

Range Suitability--The adaptability of a range to grazing by livestock and/or game.

Range Survey--(1) A determination by inspection of the carrying capacity of extensive areas of natural vegetation, based on the density and palatability of the forage. (2) an inventory which assembles important facts needed for perfecting a sound management plan taking into account the number of animals grazed, grazing capacity, period grazed, salt, needed water development, areas in need of revegetation, better livestock distribution, and the location of special problem areas.

Range Trend--The direction of change in range condition, either deterioration or improvement.

Range Type--An area of range which differs from other areas primarily by the difference in plant cover, such as grassland, browse, or conifer. One vegetation group can be distinguished from another group by difference of dominating species.

Range Woodland--Woodlands also used as range.

Rangeland--(1) Land on which the natural plant cover is composed principally of native grasses, forbs, or shrubs valuable for forage. (2) Land used for grazing by livestock and big game animals on which the natural potential climax community of plants is dominated by grasses, grasslike plants, forbs, and shrubs.

Raptors--Birds of prey, such as eagles, falcons, hawks, owls.

Rare Species--A rare species is one that, although not presently threatened with extinction, exists in such small numbers throughout its range that it may be endangered if its environment worsens.

Rat--Rattus, family Muridae; a long-tailed rodent which is much larger than a mouse. A serious pest, it is very destructive to stored food and may carry disease.

Rat Bite Fever--A disease caused by the flagellated organism Spierillum minus carried by rats and transmitted to people by their bites. Characterized by severe intermittent attacks, the ailment is not contagious. Especially prevalent in Japan.

Rat Mange--A mange caused by an infestation of Notoedres muris, a very small mite just visible to the naked eye.

Rat Poison--(1) A poison for rats obtained from the seed of a shrub, Chailletia toxicaria, native to West Africa. (2) Hamelia erecta, family Rubiaceae; a tall evergreen shrub, bearing scarlet or orange flowers and small, purple-red fruit, sometimes grown as an ornamental in warm areas. Native to tropical America. Also called scarlet bush.

Rat Typhus--A disease caused by the parasitic organism Rickettsia prowazekii; symptoms are weakness, headache, chills, and fever. It is transmitted to humans by the oriental rat flea Xenopsylla cheopis, family Pulicidae. Also called murine typhus, flea typhus.

Rate of Spread--In forestry, the quantitative increase in area per unit of time, used to describe forest fires and serious new forest disease.

Ratio Kill--The proportion or percentage of wildlife population which can be killed yearly without diminishing subsequent yield.

Ravine--A sharply cut, natural depression, V-shaped in transverse profile, usually without a permanent stream in its bottom. It has less width and size than a valley, but is larger than a gully.

Raw Land--Virgin land; an uncleared tract which is not ready for cultivation.

Raw Water--Water which is available as a supply for use but which has not yet been treated or purified.

Raw-rock Phosphate--Phosphate rock, finely ground but otherwise untreated, which is sometimes used as a slow-acting fertilizer on acid soils.

Ray--(1) In wood anatomy, a ribbon-shaped strand of tissue formed by the cambium and extending in a radial direction across the grain which serves to store food and transport it horizontally in the tree. (2) In botany, one of the small flowers radiating out from the margin of a dense inflorescence.

Ray Fungus--Actinomyces bovis; an organism widely distributed in nature which may enter the tissue of the various organs of the animal causing swelling of either the bone or soft tissue. The infection usually reaches the surface so that fistulae are established and pus-producing organisms gain entrance. It is the cause of lumpy jaw in cattle.

Razorback--(1) A type of hog with long legs and snout, sharp narrow back, and lean body; usually a half-wild mongrel breed (southern United States). (2) A sharp-ridged spur or hill.

Reaction--(1) A change in a market trend. (2) The degree of acidity or alkalinity (e.g., of a soil mass) expressed in pH values and in words as follows: extremely acid, below 4.5; very strongly acid, 4.5-5.5; medium acid, 5.6-6.0; slightly acid 6.1-6.5; neutral, 6.6-7.3 (strictly, 7.0); mildly alkaline, 7.4-8.0; strongly alkaline, 8.1-9.0; very strongly alkaline, over 9.1.

Reaeration--The absorption of oxygen in water from the atmosphere. This phenomenon enables self-purification of streams by providing the necessary oxygen to bacteria.

Reagent--Any substance involved in a chemical action.

Receiving Waters--Rivers, lakes, oceans, or other water courses that receive treated or untreated waste waters.

Recent Soil--A soil which has a profile without definite horizons of eluviation or illuviation; e.g., recently deposited alluvium. See Eluviation, Illuviation.

Receptive Hypha--A fungous hypha in a pycnium of rusts, with a female sexual function, ready to be fertilized.

Recessive--In genetics, a gene or trait which is masked by a dominant gene.

Recharge--The processes by which water is added or the amount added to the water table.

Reclamation--(1) Mining usage. The filling in of open pits, grading of the mined area, reduction of high walls, replacement of topsoil, planting, revegetation, and such other work as is necessary to restore an area of land disturbed by surface mining operations. (2) The process of reconverting mined land to other forms of productive uses. (3) Removing excess soluble salts from soils.

Reconnaissance--(1) A cruise of forest property to obtain general information of the forest conditions. (2) An extensive range survey which is carried out to estimate average density and composition of range vegetation within a type or subtype without use of systematically established plots. (3) A type of survey in which land features are examined at wide intervals and are not delineated in detail. It is intended to furnish information primarily for extensive or overall planning. See Soil Map.

Recovery Zone--The area of a stream in which active, primarily aerobic, decomposition of the pollutants is occurring.

Recreation, Outdoor--(1) Leisure-time activity such as swimming, picnicking, boating, hunting, and fishing. (2) Use of leisure time for personal satisfaction and enjoyment. It may be undertaken individually or with others. It may be planned or spontaneous. It may be passive or active, may or may not require skills and training, and may or may not require a designated area. (3) Outdoor recreation involves the protection, preservation, development, public use, and enjoyment of scenery, water, primitive or natural landscape including roadless areas), wildlife, natural phenomena (e.g., petrified wood), and archeological and historical sites.

Recycling--The process by which waste materials are transformed into new products in such a manner that the original products may lose their identity.

Red Algae--A family of algae (Rhodophyceae) most members of which are marine. They contain a red or violet pigment in addition to chlorophyll.

Red and Black Harlequin Bug--See Harlequin Bug.

Red Ash--Fraxinus pennsylvanica, family Oleaceae; a hardy deciduous tree, grown especially in the prairie states of the United States for shade, elsewhere for its lumber. Its wood is used in handles, furniture, oars, baseball bats, cabinets, boat buildings, implements, woodenware, novelties, cooperage, planing-mill products. Also called river ash.

Red Carpenter Ant--Camponotus herculeanus and C. pennsylvanicus, family Formicidae; an ant which lives in large colonies in the north temperate zone under stones, stumps, logs, and often far under ground.

Red Fir--(1) Abies magnifica, family Pinaceae; an evergreen tree grown for its valuable lumber used for general construction, boxes, crates, pulpwood, and planing-mill products. Native to North America. Also called California red fir. (2) See Douglas-fir.

Red Harvester Ant--Pogonomyrmex barbatus, family Formicidae; an ant about 1/4 inch long, with a black head and legs, and red abdomen. It lives in large colonies and makes bare circles 2 to 12 feet in diameter, with a deep nest. It is injurious to grasslands in southwestern United States because it feeds on grass seed. Also called agricultural ant.

Red Haw--Downy hawthorn, Crataeus spp. See Hawthorn. Red Hickory--Carya ovalis, family Juglandaceae; a deciduous tree grown for its valuable wood, used in tool handles, ladders, furniture, sporting goods, implements, woodenware, and for fuel and smoking meat. It is also grown as a shade tree. Native to North America. Also called mockernut, oval pignut hickory.

Red Maple--Acer rubrum, family Aceraceae; a large tree, grown as an ornamental and as a shade tree for its brilliant scarlet and yellow, autumnal foliage. Native to North America.

Red Mulberry--Morus rubra, family Moraceae; a tree which produces red or purplish-red, edible fruit about one inch long. Native to North America. Also called American mulberry. See Mulberry.

Red Oak--Northern red oak, Quercus rubra; southern red oak, Q. falcata; a tree whose lumber is valued for its strength and durability. It is also valued as lumber for constructing furniture.

Red Pine--Pinus resinosa, family Pinaceae; a quick-growing, hardy, evergreen tree, grown as an ornamental and for its valuable lumber. Native to North America. Also called Norway pine.

Red Spruce--Picea rubens, family Pinaceae; an evergreen, coniferous tree which is a chief source of paper pulp. Native to North America.

Red Tailed Hawk--Buteo jamaicensis, a hawk widely distributed across the eastern United States that is characterized by a short red colored tail. They eat large numbers of rodents and are generally considered to be beneficial.

Red Worms--Stongylus, family Strongylidae; nematodes which infest the large intestine of equines. Their red color is due to the presence of hemoglobin in the bodies of the worms, and not to blood sucked from their hosts.

Redbud--Cercis canadensis; a wild shrub that blooms in early spring. See Eastern Redbud.

Redbug--See Chigger.

Redcedar--Eastern, Juniperus virginiana; western, Thuja plicata; a tree that produces lumber valued for its fragrance and decayresisting qualities.

Redd--(1) A gravel bed in a river in which salmon lay their eggs. (2) The spawning nest which is excavated in the gravel or stones of the stream bed, filled with the eggs, and then partially refilled with coarse stones. Applied especially to the nests of the family Salmonidae.

Redox Potential--The expression for the relative state of oxidation.

Reduction--(1) The process of removing oxygen from a compound; e.g., hematite is reduced to metallic iron. (2) The addition of electrons to an atom or ion.

Redwood--Sequoia sempervirens, family Pinaceae; an evergreen tree which grows to 340 feet and is valued as an important source of lumber. Native to California and Oregon, United States. See Giant Sequoia.

Reed--(1) Any tall, slender plant, usually having coarse and jointed stems, including certain grasses and grasslike plants. (2) Phragmites communis, family Gramineae; the common reed, a widespread, perennial marsh grass with erect culms 10 to 15 feet tall, and stout, creeping rhizomes; used for making mats, thatching, cordage, and carrying nets. Native to north temperate zone and South America.

Reed Peat--A class of peat developed from reeds.

Reedgrass--Any grass of the genus Calamagrostis, family Gramineae. Species are tall, perennial grasses with creeping rhizomes, valuable as range grass and for wild hay.

Reentry Period--The length of time that is required by law between the application of certain hazardous pesticides and the entrance of people into the area without protective clothing.

Reforestation--The natural or artificial restocking with forest trees of an area previously under forest.

Refuge--(1) A tract of land set aside for wildlife protection, particularly for game animals and wildfowl. In practice, the protection afforded in a refuge is more limited than in a sanctuary. (2) In nature, a place affording protection against enemies; a shelter; a covert.

Regenerative Agriculture--A system of farming and ranching whereby resources can be used economically in perpetuity. See Iatroagriculture.

Regolith--Soil and mantle rock; saprolith. The layer or mantle of loose, incoherent rock material, of whatever origin, that forms the surface of the land and rests on bedrock. It comprises rock waste of all sorts, including volcanic ash and glacial drift.

Regression--(1) Destruction of the vegetation, as by fire, grazing, cutting, etc., usually with subsequent deterioration of the site, as by exposure, erosion, or loss of nutrients, to such extent as to give rise to a subsequent simpler vegetative type. It is not a true succession or development from forest to grassland, but a replacement as a consequence of complete destruction of the trees, etc. (2) Measure of the relationship between two variables. The value of one trait can be predicted by knowing the value of the other variable; e.g., easily obtained carcass traits (hot carcass weight, fat thickness, ribeye area, and percent of internal fat) are used to predict percent cutability.

Regulation Cut--The determination, periodically or in advance of cutting, of the volume of timber to be felled under the objectives of a given management plan.

Reindeer--Any of several species of the genus Rangifer, a type of large deer with branching horns used in Arctic regions for food.

Rejuvenate--The use of lime and fertilizer to enhance soil productivity.

Relative Age--In soil development, the appearance of the profile features; e.g., a soil along a stream may receive floodwater sediment every year or two and therefore remain relatively young in profile development.

Relative Humidity--The ratio of the mass of moisture actually present in any volume of air at a given temperature to the maximum amount possible at that temperature and pressure, usually expressed in percentage.

Relief--(1) The variation in elevation of the ground surface. It is indicated on maps by hachures, shading, or more accurately, by contour lines. (2) The physical or geomorphological features of a land surface. (3) The local difference in elevation of land features expressed in feet or in such terms as strong, mild, low, rugged.

Relief Well--A small-diameter riser extending from inside a tile drainage system to the surface air, especially at the beginning of a steeper gradient to permit uniform flow when the tile line is running full of water. The steeper gradient will cause faster water flow; this will produce a partial vacuum and restricted flow unless more atmospheric air is supplied by a relief well. Also known as relief pipe or breather.

Renewable Natural Resources--Resources such as forests, rangeland, soil, and water that can be restored and improved to produce the food, fiber, and other things humans need on a sustained basis.

Renewable Resources--Renewable energy; resources that can be replaced after use through natural means; e.g., solar energy, wind energy, energy from growing plants.

Renovate--To renew, as by pruning old wood to induce fresh growth; to fertilize and spray old lawns to produce new growth; to repair and again make usable as to renovate a machine or building.

Repellent--(1) Any substance obnoxious to insects, which prevents them from injuring their hosts or laying eggs for hatching future generations. (2) Any substance disliked by a nuisance animal, used to discourage its visits.

Reproduction Period--The time required or normally decided upon for the renewal of a stand of trees by natural or artificial regeneration.

Repulsion--In genetics, the condition in which an individual heterozygous for two pairs of linked genes receives the dominant member of one pair from one parent and the dominant member of the second pair from the other parent; e.g., AAbb x aaBB.

Research--All effort directed toward increased knowledge of natural phenomena and the environment and toward the solution of problems in all fields of science. This includes basic and applied research. Much of the agricultural productivity of the United States is directly the result of applying research.

Reserve--(1) Any tract of land, especially public land, set aside for some special use; e.g., forest reserve, school reserve. Also called reservation. (2) A tree or group of trees left uncut on an area for a period, usually a second rotating. After the stand is reproduced, naturally or artificially, an active stand which is held for future utilization.

Reserve Food--Plant food stored in the various parts of any plant, especially that stored in the roots and crowns of biennial and perennial grasses and legumes.

Reserve Soil Acidity--Potential soil acidity. See Reaction.

Resident Species--Species common to an area without distinction as to being native or introduced.

Residual--(1) Remaining in place after all but the least soluble constituents have been removed. Said of the material eventually resulting from the decomposition of rocks. (2) Standing, as a remnant of a formerly greater mass of rock or area of land, above a surrounding area which has been eroded. Said of some rocks, hills, mountains, mesas, plateaus, and groups of such features. (3) Soil developed in place from underlying bedrock. See Monadnock.

Residual Effect--The effect of a particular product or substance that remains after its initial use. Some insecticides and fertilizers remain effective for some time after they are applied.

Residual Stand--Trees, often of saw log size, left in a stand after thinning to grow until the next harvest. Also called reserve stand.

Residual Value--Of fertilizers, limes, and manures. The value of the fertilizer, lime, or manure to succeeding crops after it has been in the soil for one cropping season.

Residue--A deposit of an pesticide which persists on an exterior surface or which is absorbed by plant or animal tissue following treatment.

Residue Management--Of crops. Use of that portion of the plant or crop left in the field after harvest for protection or improvement of the soil. See Conservation Tillage.

Residues--(1) Coarse residues: plant residues suitable for chipping, such as slabs, edgings, and ends. (2) Fine residues: plant residues not suitable for chipping such as sawdust, shavings, and veneer clippings. (3) Plant residues: wood materials from primary manufacturing plants that are not used for any product. (4) Logging residues: the unused portions of sawtimber and poletimber trees cut or killed by logging. (5) Urban residues: wood materials from urban areas, such as newspapers, lumber, and plywood from building demolition, and used packaging and shipping wood materials.

Resinosis--An abnormal exudation of resin or pitch from conifers or the abnormal impregnation of their tissues by resin. Also called resin-flux.

Resins--A class of flammable, amorphous, vegetable substances secreted by certain plants and trees, and characterizing the wood of many coniferous species. They are oxidation or polymerization products of the terpenes, and consist of mixtures of aromatic acids and esters. Produced form oleoresins.

Resources--The available means for production. Land, labor, and capital are the basic means of production on farms.

Respirable Particulate Matter--That portion of the total particulate matter that has an especially long residence time in the atmosphere and penetrates deeply into the lungs. These characteristics are due to size (smaller than 2 to 3 microns).

Respiration--(1) A chemical process that takes place in living cells whereby food (fats, carbohydrates, and proteins) is "burned" (oxidized) to release energy and waste products, mainly carbon dioxide and water. Living things use energy produced through respiration to drive vital life processes such as growth and reproduction. (2) The oxidation of carbohydrates in living organisms and the attendant release of energy and liberation of carbon dioxide and water. (3) In animals, the act of breathing; the drawing of air into the lungs and its exhalation. In small organisms with no special breathing organs, the process takes place over a large part of the body surface.

Respirator--A device worn over the nose or mouth to protect the respiratory tract during the spraying of pesticides, working in dusty conditions, etc.

Rest Period--A period of quiescence or inactivity in plants even though moisture and temperature conditions are favorable for growth. See Dormancy.

Rest-rotation Grazing--An intensive system of management whereby grazing is deferred on various parts of the range during succeeding years, allowing the deferred part complete rest for one year. Two or more units are required. Control by fencing is usually necessary on cattle range, but may be obtained by herding on sheep ranges.

Rested Pasture--Pasture ungrazed for an entire growing season.

Resting Land--See Fallow.

Resting Pasture--A pasture not grazed by livestock.

Restock--To stock again; to add new or additional livestock, game, or fish.

Restorer Line--Parent plants used to restore adequate levels of fertility in hybrid crops such as hybrid sorghum or hybrid cotton.

Restricted Use Pesticide--A pesticide that can be applied only by a certified applicator. These pesticides are toxic to humans and/or pose a potential threat to the environment.

Restriction Enzymes--Enzymes used in genetic engineering to remove a gene from a piece of DNA.

Retention Reservoir--A reservoir used strictly for flood control. One or more openings at the base of the dam, open at all times, are of such size that the discharge is never more than the capacity of the stream below.

Reticulate Mottling--In oxisols, a network of coarse streaks of different colors characteristic of parent materials.

Revegetation--Reestablishment of vegetation which may take place naturally or be induced by humans through seeding or transplanting.

Reverse Osmosis--(1) An external force is used to reverse normal osmotic flow through a semipermeable membrane, resulting in movement of water from a solution of higher solute concentration to one of lower solute concentration. See Osmosis. (2) A process of desalination of seawater whereby only pure water passes through a fine membrane while the salts cannot pass through.

Reverted Phosphoric Oxide--The phosphoric oxide in phosphate fertilizers may be divided into three parts: (a) water-soluble, (b) insoluble in water but soluble in neutral ammonium citrate, and (c) insoluble in water or neutral ammonium citrate. The addition of lime, limestone, cyanamide, ammonia, or similar basic materials may cause some reversion of phosphoric oxide to less-soluble forms. Reverted phosphoric oxide is that which has been changed from the water-soluble to the citrate-soluble form or from the citrate-soluble to that phosphoric oxide that is neither water-soluble nor citrate-soluble.

Revetment--A facing of stone or other material, either permanent or temporary, placed along the edge of a stream to stabilize the bank and protect it from the erosive action of the stream.

Rhizobia--Bacteria that live symbiotically in roots of legumes and fix nitrogen from the air.

Rhododendron--Certain north temperate zone, evergreen or deciduous shrubs of the genus Rhododendron, family Ericaceae. Species are grown as ornamentals. They require acid soils.

Rice-Fish Rotation--The alternation of rice and fish crops. Rice fields, which would ordinarily lie fallow and idle, are flooded and made to produce a crop of fish for one or two years. In addition to yielding income from the fish, the land is rested and enriched for the following rice crop.

Ridge Land--Any broad or narrow, crested, elongated land feature which rises above or separates lowlands plains or valley basins, sometimes constituting a drainage divide.

Ridging--(1) Pulling the soil into a low ridge at the base of plants. Potatoes are commonly ridged or hilled to keep the tubers covered and prevent greening caused by exposure to sunlight. (2) Making small embankments or borders in fields to control irrigation water, conserve runoff from rainfall, or to assist in drainage.

Riding Down--Pushing over of small trees, shrubs, and fences by livestock in order to reach and browse in the foliage.

Riffles--Shallow rapids in an open stream where the water surface is broken into waves by obstructions wholly or partly submerged.

Riga Pine--Scotch pine.

Rill--(1) A very small trickling stream of water; a very small brook. (2) A minute stream that flows away from a beach as a wave subsides. (3) A small channel made by circulating water in the wall, floor, or ceiling of a cave. An erosion channel a few centimeters deep.

Rill Erosion--An erosion process in which numerous small channels of only several centimeters (inches) in depth are formed; occurs mainly on recently cultivated soils.

Rime--A white, icy coating on grass and leaves, formed by hoar frost, white frost, etc.

Ring--(1) A cut or girdle around the trunk, branches, or roots of a tree. See Girdle. (2) Annual growth ring of a tree. See Annual Ring. (3) (a) A circular band of metal or wood, as the metal ring in the nose of a bull. (b) To place a ring through the cartilage of the nose of an animal; e.g., to prevent a hog from harmful rooting or to control a bull, etc. (4) (a) A circular, metal or plastic band placed on the leg of a fowl for identification purposes. (b) To place a ring on the leg of a fowl. Also called ringing birds. (5) A ridge which encircles the horns of a cow, the number increasing with age. (6) A circular exhibition place for the showing or sale of livestock or the racing of horses.

Ring-necked Pheasant--Phasianus colchicus torquatus, family Phasianidae; a long-tailed, highly colored, gallinaceous bird with a white ring neck. A highly popular game bird, it is sometimes a nuisance on farms because it pulls young corn plants out of the ground and devours what is left of the kernel. It is also occasionally harmful to vegetable crops, such as tomatoes. Originally from China.

Ring-porous Wood--Any of a group of hardwoods in which the pores are comparatively large at the beginning of each annual ring and decrease in size more-or-less abruptly toward the outer portion of the ring, thus forming a distinct inner zone of pores known as the spring wood and an outer zone with smaller pores known as the summer wood.

Rio--(Spanish) River.

Ripa--(1) A stream or river bank. (2) Land which borders the water line of a river or sea.

Riparian--(1) Designating land which borders a stream or body of water. (2) Pertaining to the banks of a body of water; a riparian owner is one who owns to the edge of a body of water; a riparian right is the right to control and use water by virtue of the ownership to the bank or banks of a body of water.

Riparian Doctrine--Under common law (United States), the owner of land along a stream is entitled to have the streamflow to his land undiminished in quantity and unimpaired in quality by upstream riparian owners, except that such owners are entitled to use water for domestic purposes. In some states, it is held that the riparian right includes the right to make use of the water for irrigation purposes and other uses, and that such right is a property right entitled to protection. See Aquatic Rights.

Riparian Forest--Tree growth adjacent to streams or other watercourses whose roots are in or close to the zone of saturation due to the proximity of surface or underground water.

Riparian Habitat--That portion of a watershed or shoreline influenced by surface or subsurface waters, including stream or lake margins, marshes, drainage courses, springs, and seeps.

Riparian Owner--One who owns land adjacent to a stream or other body of water.

Riparian Rights--The rights accruing to a landowner on the bank of a natural watercourse, lake, or ocean. These rights vary with state laws. Riparian rights cease at the water's edge and do not interfere with use of the water area by others offshore.

Riparian Vegetation--Vegetation growing along the banks of a small lake, river, swamp, or spring; also known as phreatophytes, and riverine and riverain vegetation. Vegetation growing along a large lake or ocean are termed littoral.

Ripe--(1) Designating mature seeds which are fit for gemination. (2) Designating fruit which has attained full development. (3) In plant propagation, designating wood that will root well. (4) In grafting, designating that wood which is ready for perfect union. (5) Designating the best condition for use, as ripe cheese, ripe wine.

Ripe Snow--Snow which during the process of melting and settling has attained its maximum power of water suspension without loss of water. Snow is overripe when it has exceeded its ability to hold water and is losing it. The difference in density between ripe and overripe snow does not exceed 10 percent.

Riprap--Broken rock, cobbles, or boulders placed on earth surfaces, such as the face of a dam or the bank of a stream, for protection against the action of water (waves); also applied to brush or pole mattresses, or brush and stone, or other similar materials used for soil erosion control.

Rise of Salts--Soluble salts, previously distributed in the soil, which is brought to the surface with the rise of capillary water and left as a surface incrustation when the moisture evaporates. This accumulation may cause crop injury. See Waterlogged.

River--A stream of water bearing the waste of the land from higher to lower ground, and as a rule to the sea. A trunk stream and all the branches that joint it constitute a river system. Stream is a general term, with little relation to size. Rill, rivulet, brook, and creek apply to streams of small or moderate size. River is generally applied to a trunk stream or to the larger branches of a river system.

River Ash--See Red Ash.

River Bank--(1) The nearly vertical or steeply sloping ground, generally alluvium, which forms the side of the river channel. Generally, it is not as high as a bluff, although there is little distinction between the two. Banks are subject to continuous, slow erosion by river flow, or to rapid undercutting during flood periods. (2) The brim of a river or land bordering its edge.

River Basin--The area of land drained by a river and its tributaries. See Watershed.

River Bottomland--Low land which consists of alluvial deposits along a river. Generally, but not everywhere, it is composed of soil more fertile and potentially more productive than adjacent upland.

Riverain--Of or pertaining to a river.

Riverine--Pertaining to, or formed by, a stream or river systems, such as riverine erosion or riverine vegetation along the banks of a river.

Riverwash--Alluvial deposition in the channel of rivers.

Rock--(1) Any consolidated and relatively hard naturally formed mass of mineral matter; stone. (2) A peak or cliff of rock, usually bare, and considered as one mass, as the Rock of Gibraltar. (3) To the engineer, the term rock signifies firm and coherent or consolidated substances that cannot normally be excavated by manual methods alone.

Rock Cedar--Juniperus mexicana, family Cupressaceae; a tall evergreen tree grown as an ornamental and for its aromatic, brownish lumber used for making boxes, pencils, etc. Native to southwestern United States and Mexico.

Rock Disintegration--The natural process by which hard rock is disrupted and comminuted. The factors involved are: expansion and contraction due to change in temperature, the chemical and mechanical work of plant roots, movements of stone fragments down slopes through force of gravity, a partial chemical solution, abrasion by moving water, ice, and lichens. See Lichens.

Rock, Igneous--This class of rock types is often subdivided, for convenience, into plutonic rocks (those which were formed by the solidification of molten materials below the ground surface, e.g., granite) and volcanic rocks (those formed by solidification of molten materials which have been extruded onto the ground surface).

Rock, Metamorphic--Rocks which have been formed in the solid state under the conditions of high pressure, high temperature, and the introduction of new chemical substances that, in general occur at great depths within the earth, e.g., slate, marble, jade, and schist.

Rock Outcrop--A surface exposure of bedrock which may be a feature of stony land but which is distinguished from boulders or detached fragments of rock.

Rock Phosphate--The natural mineral deposit essentially tricalcium phosphate ([Ca.sub.3][(P[O.sub.4]).sub.2]), which is the principal source of the phosphorus of commercial fertilizers. The raw rock finely ground is also applied to acid soils as a fertilizer. The principal mining (United States) at present is in Florida and Tennessee, but large deposits occur in Wyoming, Idaho, Utah, and Montana, and smaller deposits occur in South Carolina, Kentucky, and Arkansas.

Rock, Sedimentary--Rocks which have been formed from deposits of sediment, whether from fragments of other rock transported from their sources and deposited by water, e.g., sandstone or shale, or by precipitation from solution or fixation by organisms, e.g., rock salt, gypsum, and limestone.

Rock Weathering--The natural processes which cause the physical and chemical disintegration and decomposition of rock; the residual mass of weathering in the parent material of mineral soils.

Rocky Mountain Crazyweed--Oxytropis saximontana, family Leguminosae; a poisonous plant found from Montana to Utah, United States, whose foliage is poisonous to cattle. Symptoms of poisoning are dullness, irregularity of gait, lack of appetite, dragging of the feet, a solitary habit, loss of flesh, and shaggy coat. As the animal ceases to eat it dies. Native to North America. See Loco.

Rocky Mountain Spotted Fever--A disease of people and animals characterized by intermittent chills and fever, painful muscles and joints, and red blotches on the skin. Occurring in the Rocky Mountain area, United States, the Rocky Mountain wood tick is the vector.

Rocky Mountain Wood Tick--Dermacentor andersoni, family Ixodidae; probably the most important tick vector of disease. This tick transmits Rocky Mountain spotted fever, tularemia, Colorado tick fever, American Q-fever, and encephalomyelitis and, experimentally, anaplasmosis. Most domestic animals, humans, and numerous wild mammals are its hosts. The stages in the life cycle are egg, larva, nymph, and adult. Larvae and nymphs usually live on small wild animals, mainly rodents; adults attack larger animals and people.

Rodent--A classification of mammals, mostly vegetarians, characterized by their single pair of chisel-shaped, upper incisors. Rodents are members of the orders Rodentia (rats, mice, squirrels, etc.) and Lagomorpha (rabbits, etc.).

Rodenticide--Any poison which is lethal to rodents.

Roe--The eggs or testes of fish. Consisting of two types, the female eggs (hard roe) and the male testes (soft roe), they are widely used for human consumption; e.g., the salted roe of sturgeon (caviar) is highly valued as a delicacy. see Sturgeon.

Roll-over Terrace--A terrace which has little height and a broad base, hence gently sloping. Under certain conditions it is effective in conserving water and reducing erosion, and it has the advantage of offering no obstacle to the movement of farm equipment over fields. See Broad-base Terrace.

Rolling--(1) Excessive side motion of shoulders, common in horses with abnormally wide fronts or chests. (2) A part of seed-bed preparation in which the land is rolled to even out the surface. (3) Processing grain through a set of smooth rollers which are close together; sometimes called flaking.

Rolling Land--A land surface which has rounded undulations, and relatively low relief.

Roof Rat--Rattus rattus alexandrinus, one of the three types of rats found in the United States, about 15 inches from tip of nose to end of tail. Its fur on the back and sides is gray to gray-brown and the undersurface of the body is almost white. It breeds four times a year with an average of six young in a litter. Also called Alexandrine rat. See Rat.

Rookery--A place where large numbers of wild birds or animals congregate and breed.

Rosin--Solidified amber-colored sap (resin) mostly from longleaf pine (Pinus palustris), occurring near the Gulf of Mexico in southern United States. Chemically it is mostly abietic acid anhydride ([C.sub.44][H.sub.62][O.sub.4]). It is used as a stiffening agent in plasters and ointments, on violins, and on the hand of baseball pitchers. Rosin was formerly known as colophony.

Ross--To remove bark from, or to smooth a log.

Rot--A state of decay caused by bacteria or fungi. See Decay.

Rotated Pasture--(1) A pasture in the regular crop rotation which is grazed for a few years, usually two or three, and then plowed for other crops. (2) A pasture which is divided into segments by use of fences: the livestock being confined to one segment at a time in a definite rotation pattern.

Rotation--(1) In cropping, the growing of two or more crops on the same piece of land in different years in sequence and according to a definite plan. One of the most widely recommended crop rotations consists of (a) a tilled crop, often corn; (b) a small grain; (c) a legume or grass crop or a mixture of legumes and grasses often for more than one year. (2) In forestry, the period of years required to establish and grow timber crops to a specified condition of maturity.

Rotation Burning--The burning of brush and meadows every three years to provide more pasture grasses.

Rotenone--The common name of a botanical insecticide; the main toxic constituent in the roots of certain leguminous plants, such as Derris elliptica and Lonchocarpus utilis and L. urucu; moderately toxic to mammals, acute oral LD50 for rats 132 mg/kg; nontoxic to plants.

Rotifer--One of the Rotifera, a class of generally microscopic, manycelled animals abundant in stagnant and fresh water and in the soil.

Rotten--(1) Designating decomposed or putrid organic matter. (2) Designating ground or soil extremely soft and yielding because of decay, or rocks partially decomposed. (3) Designating sheep attacked by rot.

Rotten Cull Trees--Live trees of commercial species that do not contain a saw log now or prospectively, primarily because of rot (e.g., when rot accounts for more than 50 percent of the total cull volume.)

Rotten Wood--Wood in a state of decay produced by an attack of bacteria or fungi.

Rough Broken Land--Land naturally so deeply and minutely dissected by stream cutting that it is nonarable. Technically, it is differentiated from badlands and gullied land.

Rough Ground--An uneven, uncultivated land.

Rough Land--Nonarable land on steep, broken slopes. It may be either stony or highly dissected by erosion.

Rough Lumber--Lumber as it comes from the saw and before it is planed.

Rough Trees--(1) Live trees of commercial species that do not contain at least one 12-foot saw log, or two noncontiguous saw logs, each 8 feet or longer, now or prospectively, primarily because of roughness, poor form, splits, and cracks, and with less than one-third of the gross tree volume in sound material. (2) All live trees of noncommercial species.

Roundwood Products--Logs, bolts, and other round sections cut from trees for industrial or consumer uses. Included are saw logs, veneer logs and bolts, cooperage logs and bolts, pulpwood, fuel-wood, piling, poles and posts, hewn ties, mine timbers, and various other round, split, or hewn products.

Rubber Tree--Hevea brasiliensis; a large tree that grows in tropical areas near the equator. It provides the principal source of the natural rubber of commerce.

Rubble--(1) Water-worn stones on a beach. (2) Rough stones in or from a quarry. (3) Any debris resulting from violent action such as a blast or an earthquake.

Rubble Dam--An unmortared dam, similar to a loose rock dam, which is made of broken stones, bricks, etc., and used in gully control in soil conservation.

Ruderal--Designating weeds which spring up on uncultivated or abandoned land.

Run--(1) A period of time, as a maple syrup run. (2) The amount of sap or sugar produced in a given time. (3) A swiftly moving tributary, rivulet, or mountain stream (eastern United States). (4) The stream outlet of a large spring (Florida, United States). (5) Unrestricted movement, as the colts have the run of the pasture. (6) An area of land or a leasehold (New Zealand). (7) A small, often dry gully or channel carved by water. See Arroyo. (8) A fenced-in pen used for the exercise of animals or poultry. (9) To feed; to graze, as steers run on the open range. (10) To operate, as a plow is set to run at a depth of 6 inches. (11) To cultivate, mow, combine, etc., as to run over a field with a weeder. (12) To maintain animals, as he runs sheep. (13) To work a dog with sheep or cattle. (14) To discharge pus, as a sore runs. (15) To be, as the prices run very high. (16) To move rapidly, as a horse. (17) To turn, as to run a wheel. (18) To grow, as when the vines begin to run. (19) To operate, as to run an engine.

Run On--To graze or pasture on, as to run on the range.

Run-off Modulus--The depth of water in inches over the under-drained area which must be removed by tile drains in 24 hours. It is a measure of the maximum rate at which the water will move through the soils to the laterals.

Runner--(1) A breed of ducks of very distinctive type, having a long, narrow body and very erect carriage. The breed derives its name from its gait, which is a quick run, quite unlike the waddle of other ducks. The adult drake weighs about 41/2 pounds; the adult duck about 4 pounds. The runner is noted as an egg-producing breed and has little or no value for meat production. Its three varieties are the White, the Fawn and White, and the Penciled. Also called Indian Runner. (2) A lateral, aboveground shoot (stolon) of certain plants; e.g., strawberries, which roots and forms young plants at some of the nodes, aiding in propagation. (3) A rope used to increase the mechanical power of a tackle. (4) The upper or rotating stone of a set of millstones. (5) A supporting attachment which slides along the ground, as a sled runner. See Stolon.

Running Fire--In forestry, a fire which spreads rapidly with a well-defined head but little crowning.

Runoff--(1) The total stream discharge of water, including both surface and subsurface flow, usually expressed in acre feet. (2) The rate at which water is discharged from a drainage area, usually expressed in cubic feet per second per square mile of drainage area.

Runup--The rush of water up a beach or structure, associated with the breaking of a wave. The amount of runup is measured according to the vertical height above still water level that the rush of water reaches.

Russian Olive--Elaeagnus angustifolia, family Elaeagnaceae; a hardy, wind-resistant, spiny shrub or small tree grown for its ornamental fruit and silvery leaves in hedges and windbreaks. Native to Europe and Asia. Also called oleaster.

Rut--(1) The grooved track left by the wheels of vehicles in soft ground. (2) The season of heightened sexual activity in male mammals that coincides with the season of estrus in the female. See Estrus.

Rutter--A female mammal, such as a cow, which for some abnormality remains constantly in heat. Also called a buller.

Rutting Season--The recurring, usually annual, period when deer, cattle, etc., are in heat. See Estrus Cycle.
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Title Annotation:Part 3: N-R
Publication:Delmar's Agriscience Dictionary
Article Type:Definition
Date:Jan 1, 2000
Words:30330
Previous Article:Part 2 Business and mechanical technology.
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