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Abiotic Environmental or nonliving components of an ecosystem.

Abiotic disease A plant disease or disorder caused by a nonliving factor, for example, air pollution.

Acre A land measurement with an area of 43,560 square feet; 4840 square yards; 4046 square meters.

Active ingredient The ingredient in an herbicide or pesticide that is the actual poison.

Adenosine triphosphate (ATP) A nucleotide used to transport chemical energy within cells for metabolism.

Adventitious root Root that arises from atypical areas on a plant such as nodes or stems.

Aerobic In the presence of oxygen.

Agrarianism A belief that promotes the idea that farming is a noble profession, the best way of life, and the most important economic endeavor.

Agribusiness The food and fiber section of the economy including all firms enga ged in producing, processing, transporting, marketing, and distribution of products that come from domesticated animals or plants.

Agricultural export Agricultural product that is sold and sent to other countries. Corn, soybean, and wheat are the largest U.S. agricultural exports.

Agriculture The process of cultivating land for the production of food, feed, fiber, and fuel from plants or animals.

Agrobacterium tumefaciens A pathogenic soil bacterium that is used to transfer genes when genetically modifying plants.

Agroecosystem Ecosystem that has been modified by inputs of fertilizers, pesticides, energy, and human labor to produce fiber, food, and shelter. Plants and animals selected for specific traits are components of agroecosystems.

Agroforestry The combination of agricultural and forestry practices to create a diverse, productive, and sustainable land-use system.

Air masses Large bodies of air that contain similar temperature and moisture content.

Alfalfa A legume that is one of the oldest cultivated forage crops for livestock feed. It is harvested as a hay or silage crop.

Alkaloid Natural nitrogen-containing compound in some plants that is bitter tasting and can produce a physiological reaction in animals. Nicotine is the alkaloid found in tobacco.

Allele One form of a specific gene that controls a certain trait.

Allelopathic A plant containing compounds that inhibit some plants' growth.

Allelopathy The adverse effect of one plant on another due to the production of a chemical inhibitor.

Alley cropping An agroforestry system in which trees are grown in rows with annual or perennial crops grown between the trees.

Alliance for a Green Revolution in Africa (AGRA) A partnership working to alleviate the poverty and hunger of millions of small-scale farmers across Africa.

Alluvial soil Rich, fertile soil that was originally deposited by rivers or moving water.

Amino acid Molecules with a common structure consisting of a central carbon (C) with hydrogen (H), an amino group (NH2), and a carboxyl group (COOH). Twenty amino acids are used in protein synthesis.

Amino acid synthesis inhibitor An active ingredient in some herbicides. It disables the enzymes responsible for the synthesis of specific amino acids.

Anatomy The study of the arrangement of cells, tissues, organs, and other structures of an organism.

Anhydrous ammonia A common form of synthetic nitrogen fertilizer that is injected into the soil from a pressurized cylinder.

The Animal and Plant Health Inspection Service of the USDA (APHIS) This organization prevents the introduction of parasitic plant pests and noxious weeds into the United States.

Annual plant Plant that completes its life cycle in one year or growing season. Winter and spring annuals are two types.

Anti-quality factor The components of forage or feed quality that reduce palatability or animal performance; includes factors such as chemical toxins or morphological features.

Apical meristem Actively dividing cells found at the tip of a plant root or shoot.

Aquatic plants Plants that grow in water.

Arid region Area of the world that receives less than 10 inches (25 centimeters) of rain annually.

Asexual reproduction Reproduction of plants through vegetative means such as rhizomes and stolons. Asexual reproduction does not involve exchange of gene tic materials.

Atmosphere The gaseous layer that surrounds the earth and extends 70 miles (113 kilometers) into space. Important atmospheric gases are nitrogen, oxygen, water vapor, and carbon dioxide.

Atmospheric fixation The process in which energy from lightning converts atmospheric nitrogen to nitrate that falls with rain or snow to the soil and is available for plants to use.

Atom The smallest component of an element that has all of the chemical and physical properties of the element. Consists of a nucleus made of protons and neutrons with electrons circling the nucleus.

Atomic number Number assigned to elements based on their number of protons.

Axillary buds and meristems Group of actively dividing cells found at the side nodes of a plant. They are responsible for the development of branch or flower buds.

Bacteria Microscopic (1 to 3 micrometers), single-celled organisms that reproduce by fission.

Barley A small grain crop that is one of the oldest cultivated crops. It is most commonly known for its use for making malt for fermentation in beer production. It is also made into breads, porridges, and soups.

Biennial plant Plant that completes its life cycle in two years or growing seasons.

Binder Machine that ties bundles (sheaves) of grain and deposits them in the field.

Biodiesel A renewable, nonpetroleum fuel that is produced from chemical processing of vegetable oil; typically the oil extracted from soybeans or canola.

Biodiversity Refers to the variety of plants and animals in a given area. It is characteristic of natural ecosystems and is important in organic farming because of the ways in which different plants and animals interact with one another.

Bioenergy Renewable energy extracted from plant biomass and animal waste that contains energy originally derived from the sun. Bioenergy crops include grains such as corn, crop residue such as corn stover, woody biomass such as willow and timber wastes, and herbaceous crops such as switchgrass and prairie plants.

Biofuel Plant material used as a fuel source. Some examples are corn for production of ethanol, hybrid willow or switchgrass for combustible pellets, grasses or legumes for conversion to biogas.

Biological magnification An increase in the concentration of a substance as it moves up a food chain.

Biological pest management A pest management method that uses a living organism to control a pest problem by predation, parasitism, or competition.

Biological weed control Using biological organisms or agents such as diseases, insects, or animals to reduce or eliminate pests.

Biomass crop Crop that is grown and harvested for the production of energy by fermentation, combustion, or gasification.

Biome Large-scale natural terrestrial ecosystem containing specific communities of plants and animals.

Biosphere The entire collection of all living things on earth in both land and water ecosystems, ranging from a few meters below the surface to a few meters above the surface.

Biotechnology The scientific techniques used to genetically manipulate living organisms to produce useful products.

Biotic The biological or living components of an ecosystem.

Biotic disease A plant disease caused by living organisms such as fungi, bacteria, viruses, and nematodes.

Biotype A population of organisms that share a similar and distinctive genotype.

Birdsfoot trefoil A legume crop that is adapted to temperate regions and used for pastures or hay.

Black layer The layer in corn and sorghum seeds that restricts translocation of carbohydrates to the seed. Its formation indicates physiological maturity of the crop.

Blade The flat surface of a plant leaf that is exposed for maximum interception of sunlight for photosynthesis. A simple leaf of a dicot has only a blade and a petiole that attaches it to the stem. A grass leaf has three components blade, sheath, and collar.

Bloat A sickness in ruminants such as cows and sheep that occurs when they graze on certain legumes. Because of the high soluble carbohydrate and protein levels, gases are trapped in the rumen forming a froth, causing the rumen to swell. Animals may die of suffocation and internal hemorrhaging.

Body mass index (BMI) An index for determining ideal body size based on age, weight, and height.

Broadcast seeding A seeding approach in which the seeds are randomly, yet evenly, spread over the top of the seedbed in a field.

Broadleaf A general term applying to dicot plants, which typically have broad leaves with netted venation.

Buckwheat An annual dicot seed crop that can be used for human and animal feed. It is not genetically related to wheat.

Bulb A swollen underground stem surrounded by concentric, fleshy rings that are modified leaves.

Bushel A unit of volume for expressing crop yield. A bushel has an 18.5-inch diameter by 8-inch deep container. Its volume is 2150 cubic inches (about 35,000 cubic centimeters). Today, grains are traded based on a standard weight per bushel.

[C.sub.3] Plants Plants that use a type of carbon fixation common in temperate plants. [C.sub.3] plants use the Calvin cycle and are called [C.sub.3] plants because the first molecule formed has three carbons (phosphoglyceric acid). Examples of these plants include wheat, alfalfa, and Kentucky bluegrass.

[C.sub.4] Plants Plants that use a type of carbon fixation in which the first stable compound formed is a four-carbon molecule (oxaloacetic acid). Examples include crops of tropical origin such as corn, sorghum, and sugarcane.

Calorie A measurement of energy content of a food or plant material. It is the amount of energy required to increase the temperature of 1 gram of water by 1 degree Celsius.

Calvin cycle The second part of photosynthesis (carbon-fixation reactions) in which carbon dioxide is turned into simple sugars.

Cane The long, flexible stem of certain plants including sugar cane, bamboo or raspberry.

Canola A crop that produces polyunsaturated oil that is used for cooking. The same species as rape, but bred to lack the inedible erucic acid found in rape.

Capillary water Water that is held in small pores within a soil and is an important source of water for plants.

Carbohydrates Energy-rich organic compounds that are composed of carbon, hydrogen, and oxygen. These include sugars, starches, and cellulose.

Carbon cycle The movement of carbon through the different reservoirs of the earth's ecosystem.

Carbon dioxide (C[O.sub.2]) A gas formed from bonding a carbon and two oxygen molecules. Carbon dioxide is the raw material for photosynthesis and plays a large role in the greenhouse effect.

Carbon fixation The conversion of carbon dioxide into organic compounds by plants through the process of photosynthesis.

Carbon-fixation reactions The second part of photosynthesis, in which carbon dioxide is turned into organic compounds.

Carbon:nitrogen ratio (C:N ratio) The relative content of carbon and nitrogen that influences the rate of decomposition.

Cassava A tropical crop that produces large roots that are 30% starch and are used to make a number of different foods depending on the local culture.

Cation exchange capacity (CEC) Cations are positively charged ions such as H+, Al+, and [Ca.sup.+]. The CEC is the amount of exchangeable cations a soil can sustain. A soil with a high cation exchange capacity holds many nutrients and is usually fertile.

Celiac disease A hereditary intolerance for gluten, a protein in cereals such as wheat.

Cell membrane disruptor Herbicides that kill plants by rupturing the cell membrane.

Cellulose A long-chained glucose polymer important to the structural support of plants. Cellulose is often linked to lignin and hemicellulose in plant cell walls.

Cereal crops Grasses that produce edible grain.

Chemical fallow The use of herbicides to keep volunteer weeds from growing in an area not planted to a crop.

Chemical pest management A pest management method that uses chemical pesticides as a way to control or suppress a plant pest.

Chickpea A legume that is grown for its edible seed, which is used in salads and soups. It is a cool-season annual.

Chilling injury Damage to plants, caused by the disruption of cell membrane integrity due to exposure to cold temperature.

Chisel plow A tillage implement consisting of a small blade attached to a shank. It does not turn the soil over, and it provides minimal incorporation of crop residues.

Chloroplast Organelle located in mesophyll cells within leaves. Where photosynthesis occurs.

Chlorophyll Green pigment within chloroplasts that absorbs photons of light energy used in the process of photosynthesis.

Cholesterol A steroid lipid in animals that is essential for membrane, hormone, brain, and nervous tissue formation. Its consumption has been associated with an incidence of heart disease in humans.

Chromosome A thread-like structure that is composed of DNA and contains genes. Each chromosome contains hundreds to thousands of genes.

Climate The typical long-term weather conditions in a region.

Clone-former A plant where the original parent plant is replaced by new plants that are established vegetatively by rhizomes, stolons or adventitious roots.

Clovers A group of forage legumes grown on considerable acreage. There are both perennial and annual species including red clover, white clover, berseem clover, kura clover, and crimson clover.

Collar An area of a grass leaf that joins the blade and the sheath. Collars can contain appendages such as auricles and ligules.

Collenchyma Plant cells that are closely compacted and provide structural support to the plant.

Combine Machinery used to harvest grain crops. Called a combine because it combines cutting, binding, and threshing of the grain into one machine.

Commodity payment Government financial support paid to farmers to ensure production of important crops and to maintain low food prices.

Companion crop A crop that is used to help establish small-seeded forage crops by providing ground cover and weed control for the slower growing forages.

Competition In plants, the process in which crops and weeds vie for limiting growth factors such as nutrients and sunlight.

Complete flower A flower that has all four flower parts stamens, pistil, petals, and sepals.

Compound leaf A leaf that has a blade composed of two or more leaflets attached to the petiole. Compound leaves may have a palmate or pinnate arrangement.

Confinement feeding When animals are kept in confined areas. This enables farmers to cut costs and create a more standardized product.

Conservation payment Government financial support used for programs aimed at reducing crop production on environmentally sensitive land.

Conservation planting Plantings of native perennial grasses or other designated woody species for the purpose of conservation of the soil from wind or water erosion.

Conservation Reserve Program (CRP) A program that rents environmentally sensitive land from landowners, who retire that land from agricultural production.

Conservation tillage A tillage approach in which 30% or more of the crop residue is left on the soil surface to reduce erosion.

Consultative Group on International Agricultural Research (CGIAR) A partnership of countries, private foundations, and international organizations that funds and directs international research institutes.

Consumer Organisms that consume producers (other organisms).

Contact herbicide Herbicide that kills vegetation by destroying cells when it is applied to the leaves, flowers, and stems of plants. Perennial plants with established root systems may not be killed by this type of herbicide.

Continuous cropping Growing the same crop on the same land for two or more years.

Continuous grazing System in which animals have uncontrolled access to a large pasture, where they are free to move around and choose the most palatable plants.

Contour strip cropping A soil and water conservation method in which annual crops are grown in alternating strips with perennial crops, and these strips follow the contours of the land rather than a straight line.

Conventional agriculture An industrialized agricultural system in which mechanization, monocultures, and chemical fertilizers and pesticides are used. The minimization of production cost is critical. Also known as the industrialization of agriculture.

Cool-season grasses Grasses that have optimum growth around 75[degrees]F (24[degrees]C). Their growth is reduced when temperatures reach or exceed 90[degrees]F (32[degrees]C).

Corm An underground stem that is compressed and solid, with outer appearance similar to a small bulb. Timothy is a perennial grass that stores energy in corms at the bases of stems.

Corn A tall-growing annual grass of tropical origin that is grown and harvested for its grain. Corn is the most economically important crop grown in the United States.

Corn Belt An area of the midwestern United States that has historically produced much of the U.S. corn crop. This area includes portions of Iowa, Illinois, Minnesota, Wisconsin, Michigan, Indiana, and Ohio.

Corn silage Silage that is made from whole corn plants, chopped into small pieces.

Cotton A crop grown in the southern United States to produce fiber.

Cover crop A crop planted to protect the soil between harvest of a cash crop and planting of the next cash crop.

Cover cropping A type of multiple cropping system in which a cover crop is grown following harvest of the cash crop.

Crassulacean acid metabolism (CAM) plants Plants with a type of photosynthesis in which carbon dioxide fixation occurs at night. This enables plants to survive very hot, dry conditions. Examples include cacti and pineapple.

Crop residue Plant material that is left on the soil after harvesting.

Crop rotation A planned sequence of different crops that are grown over the years on the same land.

Cropping system The management of crops in space and time to efficiently use the available climatic and soil resources.

Cross-pollination Pollination that occurs when the pollen of one plant fertilizes the ovule of another plant.

Crown-former A plant, often with a deep tap root, that does not spread vegetatively and relies on seeds for reproduction.

Cultivar A group of genetically similar plants of a crop species that can be distinguished from other groups of plants in the same species. Cultivars are a product of human selection, and are developed to have specific desirable characteristics.

Cultural pest management A management method that attempts to control a pest problem by manipulating the environment in which a plant or crop is growing.

Day-neutral plant Plant that flowers with any duration of day length.

Dead zone A zone in the ocean where hypoxia occurs because excess growth of plankton and algae consume all of the oxygen. A dead zone devoid of much of the normal fish and shellfish occurs where the Mississippi River meets the Gulf of Mexico.

Dent corn The most widely grown type of corn today. It originated from the crossing of flour and flint corns.

Deoxyribonucleic acid (DNA) A nucleic acid that contains the genetic information to regulate the development and functioning of living organisms. The main component of chromosomes.

Deserts Regions where annual rainfall is between 5 and 10 inches (13-25 centimeters), and daytime temperatures are high.

Determinant Varieties of soybean that cease stem elongation when the terminal meristem converts from vegetative to floral.

Developed countries Countries that have a high national income per capita (average = $30,000) and a higher Human Development Index.

Developing countries Countries that have a low national income per capita (average = $450) and a lower Human Development Index.

Development In plants, the process of growth and differentiation that includes several stages.

Dicot A plant whose embryo has two seed leaves (cotyledons).

Dicoumarol A chemical that reduces the blood-clotting ability of animals. Consumption of it can result in death from internal or external bleeding.

Dietary reference intakes (DRI) Food consumption standards developed by the U.S. government that promote healthy, nutritional diets.

Dioecious plants Plant species that have separate male and female plants. For pollination to occur, both kinds of plants must be present. An example is hops.

Direct cut silage Silage that is cut and chopped from the field in the same day.

Disaccharide Compound of two monosaccharides. Examples include sucrose (glucose and fructose) and maltose (glucose and glucose).

Disaster payment Government financial support paid to farmers when a natural disaster like drought or a severe storm occurs and damages crops, livestock, and buildings.

Disease triangle The three necessary components for a plant disease to occur: a pathogen, a susceptible host, and a favorable environment.

Disks A common tillage implement that has large, concave plates with a sharp edge to slice and mix the soil in a field.

Diurnal Daily variation, for example, the heating and cooling of a place on the earth due to variation in the sunlight reaching that place in the daytime and the nighttime.

Diversity See biodiversity.

Domestication Adapting or manipulating plants and animals to use for food production.

Dormancy When plants enter a resting stage in response to environmental stimuli. In northern latitudes, many perennial plants undergo a dormancy reaction in response to shorter days in the fall.

Double crop A multiple cropping strategy in which two crops are grown during a single growing season.

Drainage system System used to remove excess water from soil so that it does not interfere with agricultural operations and plant growth. There are two main types surface and subsurface.

Drilling A seed planting approach that deposits the seeds in a row at a uniform depth in the seedbed.

Drought Prolonged period of below normal precipitation that results in damage to crops and reduced yield.

Dry climate Climate that lacks adequate precipitation for the growth of many plants.

Dry matter The dry weight of plants that excludes moisture. This is the most commonly used measure of growth.

Dust Bowl A period in the 1930s when extreme drought and tillage caused the loss of topsoil in southern plain regions of the United States, leading to economic devastation.

Ear The female part of a corn plant that at maturity contains the corn grain on a cob.

Ecological footprint The combined environmental resources required to support the human population and absorb its waste.

Ecological pyramid The energy or resource amounts at different steps or levels of a food chain. Because loss of energy or other resources occurs within a food chain, the amounts are less at each step.

Ecological succession Process of gradual change or replacement of communities of plants over time.

Ecology The science of the mutual relationships among biological organisms and their interaction with the environment.

Ecosystem The community of organisms and their environment, and how they interact.

El Nino A condition in which the normal east to west circulation in the Pacific Ocean is altered, and warmer ocean water is moved to the Pacific coast of South America and California. This causes warmer and drier winters for the northern third of the United States and very wet conditions in the southern states.

Electron One of the three subatomic particles in an atom. Electrons have a negative charge and orbit around the nucleus of the atom.

Element Building blocks of all living and nonliving things; composed of only one kind of atom. More than 100 elements have been identified. Examples include hydrogen, nitrogen, carbon, and calcium.

Elevation The height above the average sea level. As elevation changes, the air temperature changes.

Energy The physical capacity of a system to do work.

Enriched Refined flour products that have had nutrients added to replace those lost during processing.

Ensiling The process of making silage.

Environmental Protection Agency (EPA) A government agency that is in charge of protecting human health and the natural environment.

Epidermis The outer, protective layer of cells found on all primary plant parts.

Epigeal Type of seedling emergence in which the hypocotyl lengthens and carries the cotyledons above the soil surface.

Equator An imaginary line around the earth. It is equal distance from both the North and South Poles. This divides the earth into the northern and southern hemispheres.

Erosion The detachment and movement of soil minerals and organic matter by wind and water.

Essential element An element that is necessary for a plant to complete its growth cycle, whose functions cannot be replaced by other elements. Essential elements are components of compounds such as enzymes.

Evaporation The transition of water from the liquid to gaseous state on the surface of leaves or the soil. The sun provides the energy that drives most evaporation on the planet.

Evapotranspiration (ET) Total water loss from an area of land due to evaporation from soil and plant surfaces and transpiration by plants.

Evenness The distribution or relative abundance of the individuals of a species.

Extension education service This service was established to transfer research information from universities and experiment stations to farmers and to educate farmers about best practices.

Eyes Dormant buds that are contained in tubers.

Fall equinox One of only two times a year when equal amounts of solar radiation reach both the northern and southern hemispheres. Fall equinox in one hemisphere is the same time as spring equinox in the other hemisphere. The hemisphere experiencing fall equinox will proceed to lessening solar radiation and shorter daylight hours until winter solstice.

Fallowing A strategy used in semiarid regions for accumulating moisture in the soil. A crop is not grown, and weeds are controlled using tillage or herbicides.

Farm A plot of land devoted to agriculture and the raising of crops and domesticated animals. A place where humans live and practice stewardship of the land and nature.

Farm bill Government legislation involving agriculture and food supply.

Fat Simple lipid from animals. Fats are solid at room temperature.

Federal seed laws Laws established to provide growers and other consumers essen tial information about seed they purchase. This information is found on the label of the purchased seed.

Feekes Scale A numerical scale used to assign developmental stages in grasses. The scale ranges from one (the first leaf stage) to eleven (the grain ripening stage).

Fertile Crescent An area from the eastern coast of the Mediterranean Sea to the Persian Gulf. Many plants and animals were first domesticated here.

Fertilizer An organic or inorganic material applied to the soil to promote plant growth. A fertilizer may contain a specific nutrient or may be used to increase the availability of other plant nutrients.

Fiber Associated with the structural parts of plants. Fiber can refer to a substance that is consumed in the diet from plants and that is not broken down in the digestive tract. It can also mean a plant-derived substance used to make textiles, rope, paper, and baskets.

Fiber crop Crop that produces fiber that can be extracted and used to make dura ble products. Examples include cotton and sisal.

Fibrous root system A root system that is made up of several primary roots that branch and develop many lateral roots to form an interwoven mass.

Field bean Bean that is harvested for the mature dry seeds, not the edible pods. These include navy and kidney beans. They are mostly consumed by humans but can also be used as livestock feed.

Field capacity The soil water content held in pore spaces after drainage of gravitational water. The water is readily available to plants.

Flax One of the oldest crops grown for fiber and for seed. Flax is grown today as a source of omega-3 fatty acids for human nutrition.

Flint corn Corn that has a small starchy endosperm enclosed in a thick, hard endosperm. Flint corns were likely the first types domesticated by Native Americans.

Flooding Water overflowing rivers, streams, and ponds because of excess precipitation or a high rate of snowmelt. This can cause significant crop loss.

Flour corn Has soft starch throughout the kernel and was widely used by native cultures for grinding into flour or meal. Currently, it is used for the production of tortillas and corn chip food products.

Flowers Modified leaves that contain the sexual reproductive organs of a plant. A complete flower has petals, pistil, stamens, and sepals.

Food chain The progressive flow of energy and nutrients in an ecosystem from producers through consumers.

Food Guide Pyramid A simple visual aid designed by the USDA to provide guidance to humans on proper food consumption to meet their nutritional needs.

Forage The vegetative portions of plants used for livestock feed.

Forage quality The potential forage feeding value of a crop. Features of forage quality are nutrient concentration, palatability, and anti-quality components.

Forests The most productive terrestrial biome, consisting of a dense growth of trees and underbrush.

Fossil fuels Nonrenewable fuels that come from the ancient remains of plant, animal, and microbe growth; such as oil, coal, and natural gas.

Freezing injury Occurs when ice forms in cells and damages both the cell membrane and cell organelles.

Fructose The sweetest simple sugar. Has the same chemical makeup as glucose but a different structure. Found naturally in fruits and honey.

Fruit A mature or ripened portion of a plant (often the ovary) containing a seed or seeds. May be fleshy or dried.

Fungi Biotic organisms composed of filamentous threads called hyphae that absorb nutrients for survival. Fungi may be parasites or saprophytes on plants.

Gametes Cells produced after meiosis. They contain half of the original genetic material.

Gene A sequence of nucleotides found in chromosomes. Genes control the inheritance of traits and an organism's development.

General use pesticide Pesticide that presents little danger to humans or the environment when applied according to the directions. Typically, no license is required to apply general use pesticides.

Genetic engineering Using biotechnology to produce desirable traits by altering a plant's DNA.

Genetic pest management A pest management method that uses plant breeding and genetic engineering to develop plants that are more resistant to significant plant pests.

Genetically modified organisms (GMOs) Organisms that have had a desirable trait added to them through the process of genetic engineering.

Genotype The entire genetic component of an organism.

Genus A group of related species. Also the first part of the scientific name of plants and animals.

Germination The onset of growth of a new plant from a dormant state within a seed.

Caused by favorable water, temperature, and light conditions.

Global warming An increase in the average global temperature over the past 100 years due to enhancement of the greenhouse effect caused by increasing concentrations of atmospheric gases.

Glucose The most abundant simple sugar, a six-carbon monosaccharide. The first product of photosynthesis that is metabolized and used for formation of complex carbohydrates.

Gluten A compound protein that is found in certain types of wheat.

Glycogen A long-branched chain polymer of glucose. The only carbohydrate that occurs in animals.

Glyphosate The common name for a nonselective, contact herbicide. The most widely used herbicide.

Grain crop Crop in which the grain is harvested, for example, corn, soybean, and wheat.

Grain drill A type of drill used to plant seed, generally small grains, in narrow rows that are often only 6 inches apart.

Grasslands Regions where grasses dominate the vegetation growing in the region.

Gravitational water Water that drains through the soil and is not held in the soil pores.

Green manure crops Fast-growing crop plants that are incorporated into the soil while still vegetative, with the intent of improving nutrients and soil quality.

Green Revolution The use of high-yielding crops combined with the use of fertilizers and pesticides to increase global food production especially in tropical regions.

Greenhouse effect A natural process in which the atmosphere absorbs solar radiation reflected off of the earth's surface. The main greenhouse gases are water vapor, carbon dioxide, methane, and nitrous oxide.

Gross Domestic Product (GDP) The measure of the value of a nation's total production of goods and services.

Ground tissue A primary plant tissue--other than the epidermis or conducting tissue--whose function is to provide a plant with storage and support.

Growth Increase in weight or size of an organism because of an increase in the number and size of cells.

Growth regulator A selective herbicide that disrupts plant growth by interfering with hormones and protein synthesis.

Habitat The particular place providing the resources for a plant or animal to live.

Harrow A secondary tillage implement used to smooth and level the soil surface and reduce soil particle size.

Harvest The manual or mechanical removal of a crop's grain or biomass from the field. For grain, this occurs at the completion of the crop production cycle.

Harvest maturity The moisture content of the crop when a combine can harvest the grain with minimal field loss.

Hay Forage that has been dried in the field to 15-20% moisture concentration and stored in aerobic conditions.

Hay crop silage Silage made from alfalfa and other grasses. It can also be made into hay. It is lower in energy but higher in fiber and protein content than corn silage.

Haylage Hay crop silage that is dried to a moisture content of about 50%. See wilted silage.

Heat injury Injury to plants caused by overly high temperatures, which interfere with the plant's metabolic processes.

Hemp A tall-growing annual native to Asia. It is one of the oldest fiber crops used for textiles, paper, and construction.

Herbicide A chemical agent used to kill plants. It is the most common form of weed control.

Herbicide resistance When weed species that were once susceptible to herbicides develop an ability to survive treatment with the herbicide.

Herbicide tolerance An ability to withstand treatment with a herbicide that is specifically selected for or genetically engineered into a crop.

Heritability The proportion of a phenotype that is controlled by genetic material.

Heterosis Also known as hybrid vigor. The phenomenon in which the [F.sub.1] offspring of two inbred parents has a superior phenotype due to increased heterozygosity in its genotype.

Heterozygous An organism that contains different alleles for a given trait.

High density lipoprotein (HDL) Complex associations of cholesterol, lipids, and protein that transport and deposit cholesterol. HDL is considered good cholesterol because it helps remove other forms of cholesterol from the blood.

High fructose corn syrup Widely used, inexpensive sweetener formed by processing corn grain. It is a blend of fructose and glucose. It has a higher proportion of fructose than normal corn syrup, and is the main sweetener used in soft drinks, fruit juices, candies, and processed foods.

Hobby farm Farm characterized as being highly dependant on off-farm income. Hobby farms average 100 acres (41 hectares) or less and earn less than $10,000 annually in farm sales.

Homestead Act of 1862 This act provided a U.S.citizen, 21 years or older, the right to claim 160 acres (65 hectares) of public land with the provision that the homesteader had to live on the land for five years and make improvements.

Homozygous An organism that has only one type of allele for a given gene.

Horizon A distinct layer of a soil profile formed due to weathering, leaching, humus formation, or other processes.

Host A plant infected by a pathogen or parasite.

Hot spot A circular, localized area of diseased plants in a field due to a nematode infection. An important diagnostic indication of nematode diseases.

Humid region Area of the world with more than 40 inches (102 centimeters) of precipitation in a year.

Humus A complex part of soil organic matter consisting of waxes, lignin, and carbon fractions that are resistant to decay.

Hunting and gathering An early human lifestyle in which the daily search for food by hunting and gathering of animals, seeds, and roots was a preoccupation and necessity for survival.

Husking or Shucking The process of removing the leaf-like covering from an ear of corn.

Hybrid In crop breeding, the offspring of a cross between two distinct types of one crop species. Also, the offspring that result when two organisms from different species reproduce.

Hybrid corn Corn resulting from the crossing of two inbreds. Hybrid corn seed is sold by commercial seed companies and is the primary type grown by producers today.

Hybridization Crossing two parent plants of differing genotypes to produce a hybrid.

Hydrophyte Plant that grows in water and has the ability to extract oxygen from water. For example, wild and cultivated rice.

Hypogeal Type of seedling emergence in which the cotyledons remain beneath the soil surface and the epicotyl emerges from the soil.

Hypoxia A condition of reduced concentrations of dissolved oxygen in water; caused by high nutrient levels which lead to excess growth of microorganisms. See Dead Zone.

Imperfect flower An incomplete flower that lacks either the stamen (male) or the pistil (female) components. An example is corn.

Inbred Selected plants are self-pollinated to create a uniform variety. Inbred plants are later crossed to produce hybrids.

Incomplete flower A flower that lacks one or more of the four flower parts: stamens, pistils, petals, or sepals.

Indeterminant Varieties of soybean that have continual stem elongation throughout the growing season.

Industrial fixation The process of taking ionic nitrogen ([N.sub.2]) from the air and converting it to nitrogen-bearing compounds to be used as fertilizers, such as anhydrous ammonia, urea, or ammonium nitrate.

Industrialization of agriculture Modern farms are considered to be industrial factories producing raw materials for the food industry. The minimization of production cost is critical. Also known as conventional agriculture.

Inert ingredient Ingredients that are added to herbicides to aid in the handling and application process and to increase the activity of the herbicide.

Inflorescence A flower composed of a cluster of individual flowers or florets.

Inorganic fertilizer A fertilizer that is synthetic or mined; may supply either a macroor micro-element. Examples are urea, a nitrogen source; and potash, a potassium source.

Intake The amount of food a livestock animal will consume.

Integrated pest management A strategy that incorporates five management methods (cultural, biological, mechanical, genetic, and chemical) to control plant pests. It examines all possible methods and determines which are economically feasible and environmentally sound for the pest problem involved.

Intercalary meristem Actively dividing cells that are independent of the apical meristem and are responsible for the growth of the internodes and leaves of grasses.

Intercropping The system of growing two or more crops on the same piece of land at the same time. Also called polyculture.

International research institutes Region-specific institutes that work to help improve locally important crops and their production. These were vital components of the original development of the Green Revolution.

Internode The portion of the stem between the nodes.

Inulin A unique polysaccharide of fructose. The primary storage carbohydrate in the roots and tubers of the composite family, such as Jerusalem artichoke and dandelion.

IPAT equation An equation used to look at the environmental impact of resources used and wastes generated by a human population.

Irrigation The process of application of water to meet plant needs. Irrigation is typically applied with sprinkler or flood systems, but "drip irrigation" is used for some high-value fruit and vegetable crops.

Jerusalem artichoke A member of the sunflower family used as a starch crop. It stores energy in tubers as inulin. It was used by Native Americans and colonists as an energy source but has a very small market in the United States today.

Koppen system A system developed by Wladimir Koppen, a German climatologist, dividing the earth into climate regions based on temperature and precipitation. This system also identifies five major climate types along with subclimates.

Lactose A disaccharide from glucose and galactose that is found in human and cow's milk. It is less sweet than sucrose and supplies about 50% of the energy found in cow's milk.

Latitude A measurement in degrees of north or south position on the earth. Ranges from 0[degrees] at the equator to 90[degrees] at the poles. Latitude and longitude systems were originally developed to aid in navigation and mapping of locations on the earth.

[LD.sub.50] A measurement used to measure toxicity of herbicides and pesticides. LD50 represents a single dose in milligrams of substance per kilogram of body weight that will kill 50% of a particular population.

Leaves Primary organs in plants. Responsible for the essential processes of light interception, photosynthesis, and transpiration.

Legumes Any plant belonging to the family Fabaceae, most notably known for their ability to fix atmospheric nitrogen into the soil. Examples are alfalfa, clovers, and beans.

Lentil A cool-season annual legume native to the region east of the Mediterranean Sea. It produces high-protein seeds mostly used for human food.

Light intensity Refers to the brightness of light and is affected by time of day, latitude, season, and topography of the land.

Light quality Described in terms of wavelength of sunlight. Plants are adapted to a specific light quality, which they use for photosynthesis.

Light reaction The first part of photosynthesis in which energy from light is caught in chloroplasts.

Lignification Lignin is a complex polyphenolic compound that is an important structural compound in plants and that is resistant to microbial degradation. Lignification is the process of lignin binding with cellulose and hemicellulose in the cell wall, thereby reducing their digestibility.

Linseed oil Highly unsaturated oil that is contained in flax seeds and is used in paints and wood finishes.

Lipid synthesis inhibitor A selective herbicide that prevents the formation of fatty acids, which are important for lipid synthesis, and thus disrupts formation of cell membranes.

Lipids A class of organic compounds that includes fats and oils, which are high sources of energy for the human body.

Living mulch The system of planting annual grain crops into a living but suppressed perennial sod that is able to recover after the grain crop is harvested.

Lodging Refers to the toppling of the stems of a crop plant or stand Long-day plant Plants that flower when the photoperiod is longer than a certain period.

Longitude Describes the location of a place on the earth east or west of a north-south line called the Prime Meridian. Given as a measurement using 0[degrees] at the Prime Meridian to +180[degrees] eastward and -180[degrees] westward.

Low density lipoprotein (LDL) Complex compound of cholesterol, lipids, and proteins that transports and deposits cholesterol. LDL is considered a bad cholesterol because it deposits cholesterol in the arteries of the heart.

Lupine A high-protein legume that is native to the Mediterranean region. It can be fed to poultry, swine, and cattle but is not widely grown because its main competitor, soybean, is more profitable.

Macronutrient Any essential elemental nutrient that is required in large amounts.

Malnutrition A nutritional situation where one or more essential nutrients are lacking despite sufficient caloric intake.

Maltose A two-glucose disaccharide found most frequently in germinating seeds during the breakdown of starch.

Mass selection A plant improvement strategy in which individual plants with a superior identifiable trait are selected from a population and used for the planting of the next generation.

Maturity groups A classification of soybean into 13 different groups based on photoperiod response. Each group is adapted to specific latitudes and growing season length.

Mechanical pest management A pest management method that attempts to manipulate the crop's or plant's environment by using mechanical or physical means to make it less favorable to the pest.

Mechanical weed control Weed control performed with tillage implements.

Meiosis A type of cell division in which the genetic content of the daughter cells is reduced by half. One cell undergoing meiosis produces four cells called gametes, each with half of the total genetic material of the parent.

Meristem An area of a plant with actively dividing and differentiating cells.

Mesophyll The tissue of the leaf between the upper and lower epidermis. Where photosynthesis takes place.

Mesophytes Plants that are adapted to both tropical and temperate regions and depend on precipitation for growth.

Mesopotamia An area of the Fertile Crescent that was a flat flood plain bordered to the north by the Zagros Mountains and the Arabian Desert to the south. It is the large area between the Tigris and Euphrates rivers in present-day Iraq. Because of the environmental diversity here, it was an optimal place for agriculture to develop.

Metabolism All the biochemical reactions throughout the body and their regulation.

Metamorphosis The gradual developmental (growth) stages of an insect's life cycle from egg to adult.

Methane A greenhouse gas produced in fermentation reactions by ruminant animals, such as cattle, in manure holding areas and wetlands.

Micronutrient Any essential elemental nutrient that is required in small quantities.

Mid-latitude climate A type of climate with either warm summers and mild winters or with warm summers and cold winters.

Milk line A line that forms on corn kernels when the kernel is drying down and approaching maturity.

Minerals Inorganic compounds that exist as positively or negatively charged ions. Also can be components of larger compounds.

Mixed intercropping A type of polyculture in which two or more crops are grown together randomly. An example is an alfalfa-grass mixture or a perennial prairie plant mixture.

Mode of action The biochemical mechanism herbicides use to kill plants. For example, a photosynthesis inhibitor.

Moldboard plowing The traditional, primary tillage approach that shears off a section of soil and turns it over, incorporating crop residue into the soil but leaving the soil surface vulnerable to erosion and organic matter loss.

Molecular marker Segment of DNA that aids in the selection process of useful traits or alleles.

Mollisol A soil with an A horizon that is very fertile and high in organic matter. These soils are important for crop production and are found in the grasslands of the central United States.

Monoecious plants Plants that have separate male and female flowers on the same plant. Corn and wild rice are examples.

Monocot A plant whose embryo has only one seed leaf or cotyledon.

Monoculture A system in which a single crop is grown in a field during the growing season.

Monosaccharide Simple sugar; the basic building blocks of carbohydrates. They cannot be broken down into smaller compounds from reacting with water or human digestion. Includes glucose, fructose, and galactose.

Morphology The study of the form and structure of plants.

Mulch Crop residue left on the soil surface.

Mulch tillage Tillage system that uses the chisel plow and minimal incorporation of residues.

Multiple cropping Producing two or more different crops in succession from the same piece of land in a year.

Mutation A permanent, heritable change in nucleotide sequence of a gene.

Mycoplasma-like organisms Microscopic organisms that are found in the phloem of a plant and cause plant diseases. Also called phytoplasmas.

Mycotoxin A poisonous chemical produced by certain fungi that is harmful to people and animals when ingested.

Nematode A microscopic (300-1000 micrometers), nonsegmented, roundworm that may be parasitic to plants or animals.

Neutron One of the three subatomic particles that makes up an atom. Neutrons have no charge and are located in the nucleus of the atom.

Niche The specific range of environmental conditions including light, terrestrial or aquatic conditions, temperature, and nutrients to which a species is adapted.

Nicotinamide adenine dinucleotide phosphate (NADPH) A compound found in the chloroplasts. It is produced in the light reactions of photosynthesis and used in the Calvin Cycle.

Nitrate One nitrogen atom bonded with three oxygen atoms form N[O.sub.3]. Nitrate is soluble in water and leached from the soil.

Nitrogen cycle A cycle that describes the transition of nitrogen from atmospheric nitrogen to organic nitrogen.

Nitrogen fixation A biological process carried out by bacteria, some of which live in symbiosis with plants and some of which are free-living in the soil. Atmospheric nitrogen is converted into ammonium and eventually amino acids to be used by plants.

Nitrogen reservoir The amount of nitrogen available in an ecosystem. Plants are unable to use nitrogen in its elemental form ([N.sub.2]) because it is very chemically inactive; therefore, the limiting nutrient is nitrogen.

National Organic Program (NOP) Federal regulatory agency that governs organic agriculture production.

Node The enlarged portion of the stem to which leaves are attached and where vegetative and floral buds develop.

Nodule Tumor-like growth on the roots of legumes caused by infection with symbiotic bacteria called rhizobia. The site of symbiotic nitrogen fixation.

Nonselective An herbicide that will kill almost all plants.

Nontarget Plants that are not the target of herbicide application but are sometimes affected.

No-till A tillage approach where specialized planters with disk openers slice through crop residues and precisely drop seed at the desired depth. This tillage has minimal crop residue disturbance and therefore minimizes soil erosion while maximizing soil organic matter and conserving soil water.

No-till grassland drill A type of seed-planting implement used to interseed pastures or grasslands.

Noxious weed An especially difficult to control weed that can injure crops, other useful plants, livestock, poultry, or other agricultural interests.

Nutrition The food diet consumed by humans not only for survival, but also for maintaining good health and fitness.

Nutritive value The content and availability of nutrients in a food.

Oats A small grain domesticated later than most other small grains. It is relatively high in fiber and protein content and is commonly used as a horse feed.

Obesity An extreme form of malnutrition where a person's body weight exceeds recommended levels by 20% or more.

Obligate parasite Organisms that require living host tissue to obtain nutrients for survival.

Oil Simple lipids from plants. They are liquid at room temperature.

Oil crops Crops that produce oils containing fatty acids in varying concentrations. For example, canola, soybean.

Omega-3 fatty acids Acids such as linolenic acid that have significant health benefits and are not produced by human bodies. Therefore, they must be gained through foods such as meats and flax seed.

Organic agriculture An ecological production system that encourages minimal use of off-farm inputs, the use of biodiversity, and other biological cycles and activity for crop and livestock production. Synthetic inputs cannot be used.

Organic fertilizer A fertilizer that is derived from living matter.

Organic matter The portion of the soil that includes animal and plant residues in varying stages of decay.

Orographic effect Wet conditions on the windward side of mountains and dry conditions on the leeward side of mountains. This is caused when air is uplifted when it reaches the mountains and cools, precipitating its moisture on the windward side of the mountain.

Ozone layer The layer in the atmosphere that absorbs the ultraviolet light that is extremely harmful to humans and plants.

Parasitic flowering plant An obligate parasite that lacks a root system and instead uses a haustoria to absorb water and nutrients from its host.

Parenchyma Plant cells containing chlorophyll that are sites of photosynthesis and energy storage.

Parent material The weathered rock from which soils are formed.

Pasture Area of land, usually fenced in, where plants are grown for grazing animals. Unfenced grazing areas are called "range."

Pathogen An organism or body capable of causing disease.

Peanut A legume grown for its edible, underground seed. Peanuts are consumed whole as a snack food, as peanut butter, and in candy.

Pedigree selection A method of selection that is commonly used after hybridization. Plants are selected over multiple generations to produce a uniform product.

Peg The elongated ovary of the peanut plant which buries itself in the soil after pollination to form the peanut. Peanuts are harvested by digging the crop.

Perennial Plants that live for three or more years.

Perfect flower A flower that has both a stamen (male) and pistil (female) component.

Permanent wilting point The soil moisture at which a plant wilts because the water in the soil is unavailable to the plant.

Petal The showy, modified leaf of a flower. Important for attracting pollinators.

Petiole A leaf's stem by which it is attached to the plant.

Phenotype The observable characteristics of an individual plant that can be due to genotype, environment, or the interaction of both.

Phloem Part of a plant's vascular system that transports photosynthetic food products and carbohydrates from the leaves to other plant parts.

Phospholipid A type of fatty acid. An essential component of the membranes of plants.

Photoperiod The number of hours that light is present.

Photoperiodism Flowering or dormancy response of plants to changing lengths of day and night.

Photosynthesis A process in which plants use the energy they capture from the sunlight to produce sugars that are stored or used in respiration by the plant.

Photosynthesis inhibitor A type of herbicide that prevents plants from performing photosynthesis.

Physiological maturity The stage of development of grains when the maximum accumulation of dry matter in the seed has occurred.

Phytochrome Pigment in plants that detects the changes in proportion of red and far red light.

Pigment inhibitor A selective herbicide that prevents plants from forming chlorophyll.

Pistil The female portion of a flower that contains the ovary, style, and stigma.

Plant disease Any deviation that interferes with a plant's normal development, appearance, or function and that progresses over time.

Plant succession The naturally occurring long-term changes in a plant community's structure.

Planting date A recommended date that is optimal for crop establishment and that will maximize the capture of solar energy during favorable growing temperatures.

Planting depth The optimal depth at which a seed can germinate and emerge from the soil to grow.

Planting rates The number of seeds planted, or plants transplanted, so as to optimize the light interception and use of soil moisture throughout the growing season.

Pod corn A primitive type of corn in which each individual kernel is enclosed in a pod or husk. This type of corn is primarily used for ornamental purposes.

Polar climates This climate has extremely cold winters and cool summers and is not of any agricultural significance.

Polyculture Growing two or more crops together at the same time on the same piece of land. Also known as intercropping.

Polyploid Organism that has more than one set of chromosomes.

Polysaccharide Organic molecule consisting of many monosaccharide units joined together that can function as energy storage or structural compounds.

Popcorn This corn has endosperm characteristics similar to flint corn, but the kernel is smaller. When heated, its soft starch has expansion properties that are unique compared to that of other soft starch corns. Commonly eaten as a snack food.

Pore space Area of space between soil particles that contain air or water. The larger the soil particles, the larger the pore spaces.

Postemergence Herbicide applied after the crop and weeds have emerged from the ground.

Postharvest Herbicide applied after harvest but before tillage.

Potato A bushy annual plant grown for its starch-containing tubers. It is among the five most important crops in the world.

Precipitation Water that falls in the form of rain or snow.

Preemergence Herbicides applied before the crop and weeds have emerged from the ground.

Preplant Herbicides applied before the crop is planted.

Price support program A financial payment provided by the United States Department of Agriculture (USDA), giving an incentive to grow specific crops.

Primary consumer Consumer who eats primary producers. Also known as herbivores.

Primary producer Organism that captures the sun's energy to produce its own chemical energy in the form of glucose. Examples are green plants and algae.

Profile A vertical section of soil extending from the surface to the unweathered rock of the earth's crust.

Protein A complex substance made of amino acids. A vital part of human nutrition. It is found in plants and to a larger extent in meats.

Protein crop Crops such as soybean, peas, and peanuts that produce seeds naturally high in protein.

Proton One of the three subatomic particles that makes up an atom. Protons have a positive charge and are in the nucleus of the atom.

Pseudo-annual Perennial and biennial plants managed as annuals.

Pulse Legume that has edible, high protein seeds. These include soybeans, edible field beans, field peas, peanuts, and others.

Pure live seed The viability of seed and its purity from weed seeds and other inert matter.

Qualitative Simple traits such as flower color that are controlled by one or only a few genes.

Quantitative Complex traits such as height and yield that are controlled by many genes.

Reaper A machine that cuts (and sometimes binds) grain, depositing it on the field.

Red clover Short-lived perennial used for hay, silage, and pasture.

Refining A flour production process in which the white endosperm is purified of germ and bran.

Resin A viscous liquid secreted by many plants, especially coniferous trees.

Respiration The conversion of sugars and starches to energy for use in metabolism of living cells.

Restricted use pesticide Herbicide or pesticide that is harmful to humans and the environment even when used as directed. Applicators of restricted use pesticides must be licensed.

Rhizobia Nitrogen-fixing soil bacteria that form symbiotic relationships with legumes.

Rhizome A stem that runs horizontally belowground and is a means of asexual reproduction of plants.

Rice One of the oldest and most widely cultivated crops in the world. It is a grass that grows best in extremely wet conditions.

Richness The number of species in an ecosystem or number of crops in an agroecosystem.

Ridge till A tillage approach in which ridges of soil (6 inches [15 centimeters] high) are created during final cultivation of a row crop so that in a subsequent year the crop can be planted directly into the ridge that becomes warmer and dries faster in the spring than surrounding soils.

Root The plant organ responsible for anchoring a plant to the soil and for absorbing water and essential nutrients and minerals. Roots of some plants such as alfalfa, sugarbeet, and sweet potato are also used for storage of energy reserves.

Root crop Crop grown for the starches stored in its roots.

Rotation effects Consequences resulting from crop rotations such as an increased yield in subsequent crops.

Rotational grazing The dividing of pastures into three or more sections and movement of grazing animals from section to section, to regulate animal grazing and give pasture plants a rest between grazing events.

Roundup Glyphosate. The brand name of a herbicide that is widely used because it kills a wide variety of weeds while not hurting resistant crops.

Row crop planters A type of drill that deposits seed in rows 20-30 inches (51-76 cm) apart with very precise seed metering that drops the seed at specific spacing within the row.

Ruminant An animal group that can digest cellulose. Their digestive system includes a multi-chambered stomach including the reticulum, rumen, omasum, and abomasum.

Rye A small grain crop that tolerates low fertility soils better than other small grains.

Safflower A relative of the sunflower that is grown to produce oil from its seeds, which is used for cooking and commercial purposes.

Sainfoin A perennial legume adapted to dry soils of the western United States. Used as a hay and pasture legume.

Salinity The amount of soluble salts in a soil.

Saprophyte Organism that digests dead organic matter to obtain nutrients.

Saturated fatty acids Long-chain fatty acids containing only single bonds between carbon atoms (that is, they are completely saturated with hydrogen). Most animal fats are saturated fats.

Scientific name A binomial naming system that allows for the universal identification of plants and animals. The name consists of two parts the genus and the species. The scientific name is italicized, and the genus is always capitalized.

Sclerenchyma Plant cells that have thickened, lignified cell walls that provide structural support to the plant.

Season A division of the year based on changes in weather. The weather changes because of variation in the length of the day and the amount of solar radiation that reaches the earth's surface.

Secondary consumers Consumers that eat the primary consumers. Also known as carnivores.

Section A land measurement with an area of 1 square mile (640 acres; 259 hectares).

Seed The mature, fertilized ovule or egg within the ovary that contains a plant embryo.

Seed bank The reservoir of viable but dormant seeds in or on the soil.

Seed certification A process to ensure genetic uniqueness and quality of seeds and allow for orderly production of the seed for consumer use.

Seed dispersal The means by which seeds are moved to other areas away from the parent plant.

Seed dormancy A period when a seed is quiescent. Development of the embryo is temporarily suspended.

Seeding rate The number of seeds planted, assuming a certain level of mortality, to produce a plant population that will optimally use all resources available.

Seedling growth inhibitor A selective herbicide that affects the growth of roots and shoots of germinating seedlings.

Selection In plant breeding, the process by which breeders choose individual plants with superior characteristics from a larger population.

Selective herbicide Herbicide that affects only certain species of plants.

Self-pollinated Plants that are able to pollinate themselves. These plants are usually genetically homozygous.

Semiarid region Areas that get 10-20 inches (25-51 centimeters) of precipitation annually.

Semi-humid region Areas that get 30-40 inches (76-102 centimeters) of precipitation annually.

Sepal The green, leaf-like structure located at the base of the petals of a flower.

Sheath The lower portion of a leaf that surrounds the stem (found in grasses).

Sheave Bundle of small grain stalks.

Shelling Separating corn kernels from the cobs.

Shock Bundle of grain plants.

Short-day plant Plant that flowers when the photoperiod is shorter than a certain period.

Sign Any structure or by-product produced by the pathogen that appears on or in the infected plant.

Silage High moisture forage that is stored anaerobically in a silo.

Silk The stigma and style of the corn plant.

Simple leaf A leaf that has a single blade and petiole.

Sisal A native crop of Central America that is used to produce fiber for making twine, floor mats, and rope.

Small grains Grain crops whose seeds are small relative to corn seeds. These include wheat, oat, barley, and rye. The term is not generally used for small-seeded close relatives of corn, such as sorghum.

Soil The biochemically weathered, uppermost layer of the earth's crust. It is a unique ecosystem and an essential resource for the production and growth of plants and crops.

Soil fertility The ability of a soil to supply important chemical nutrients and essential elements to a plant.

Soil organism Biotic (living) entity that lives in the soil and is essential for nutrient cycling and overall soil functions. These include fungi, bacteria, earthworms, insects, rodents, snakes.

Soil texture The fineness or coarseness of a soil; it is determined by the type and amount of specific soil particles: sand, silt, or clay.

Solar energy Energy from the sun, which has a tremendous effect on the climate of the planet and is the driving force for photosynthesis.

Sorghum A vigorous annual grass that resembles corn. It can be used for grain production, whole plant feeding to livestock, silage, ethanol production, or grazing. It is more tolerant of low rainfall than is corn.

Soybean One of the oldest cultivated crops, this legume has a number of different uses including vegetable oils, biodiesel, and protein for humans and livestock.

Species Each unique type of organism is a different species. Individual members of a species share a similar genotype, phenotype, and environmental function.

Spelt A subspecies of wheat that is low in gluten and may be easier to digest.

Sprayer The mechanical device used to apply herbicides and pesticides to crops.

Spring equinox One of only two times a year when equal amounts of solar radiation reach both the northern and southern hemispheres. Spring equinox in one hemisphere is the same time as fall equinox in the other hemisphere. The hemisphere experiencing spring equinox will proceed to increasing solar radiation and longer daylight hours until summer solstice.

Stamen The male component of a flower, composed of a filament and a pollen-bearing anther.

Starch A glucose polymer that is the most consumed carbohydrate in human diets. It is the primary energy storage form in corn grain and alfalfa roots.

Stem The main stalk or shoot of a plant found aboveground, which provides the supporting structure of the plant as well as a channel for movement of water, nutrients, and products of photosynthesis.

Stocking rate The number of animals per acre on a pasture or range.

Stolon A horizontal, aboveground stem also called a runner. Plants use it to spread and produce new plants. For example, strawberries.

Stomata Very small openings in the epidermis of a plant that aids in the exchange of water vapor, carbon dioxide, and oxygen. Singular: stomate.

Storage The procedure by which products of the harvest are saved for future use after the completion of the crop production cycle.

Storage fungi Fungi responsible for reduction in the quality of grain during storage.

Stover The leaves and stalks of corn.

Stratosphere The layer of the atmosphere from 8 to 30 miles (13-48 kilometers). This layer contains the ozone layer.

Strip cropping A polyculture strategy in which different crops are grown in monocultures in adjacent strips. Contour strip cropping is a variation of strip cropping that is used for erosion control.

Subtropical climate Moist, mid-latitude climate with mild winters.

Subsistence agriculture An agricultural lifestyle that provides only enough basic goods (food, shelter, and clothing) for survival.

Sucrose The most important disaccharide. It is composed of one glucose and one fructose. It is a widely used sweetener throughout the world and is known more commonly as table sugar.

Sugar beet One of the leading sugar crops in the world. Grown for its root, which when harvested, contains between 18% and 20% sugar.

Sugarcane One of the leading sugar crops in the world. It is harvested for its cane (stem), which contains between 12% and 15% sucrose.

Summer solstice The longest day of the year. For the northern hemisphere this is 21 June; for the southern hemisphere it is 21 December.

Sunflower A native flower of North America, this plant is grown today for its seeds, which can be used to produce oil for salad dressings and cooking. Seeds can also be eaten as a snack food.

Sustainable agriculture Agriculture that maintains soil and environmental resources for future generations and provides accountable and profitable production of food, fiber, or energy to meet societal demands.

Swathing The process in which the grains are mowed, deposited on the ground, and dried in the field.

Sweet corn Corn that has high sugar content and no starch. This type of corn is commonly eaten fresh because of its sweet taste.

Sweet potato A crop that stores energy as starch in modified roots. These roots also contain sugar which results in the sweet taste. A good source of dietary vitamin A.

Sweet sorghum A variety of sorghum that contains high stem sugar and is used for sugar production.

Sweetclover A legume not widely cultivated for harvesting but rather planted as a soil conservation crop because it grows rapidly and reseeds itself; or a green manure crop because it can produce more nitrogen than any other legume.

Symptom A response by a plant to a pathogen that is visible to an observer; for example, stunting, leaf curling.

Systemic herbicide Herbicide that is taken up by the shoots or roots of the plant and then dispersed through the plant's vascular system.

Taproot A root system that consists of one large primary root with small lateral roots.

Tassel The male reproductive part of a corn plant.

Taxonomy A system of organizing all life based on similar genetic or morphological characteristics.

Temperate The zone that lies between the tropics and the Arctic or Antarctic Circles (that is, from 23.5[degrees] to 66.5[degrees] latitude north or south) Has very distinct winter and summer seasons.

Temperature The measurement of the intensity of heat or energy content of the air, inert matter, or organisms.

Terrestrial plants Plants that grow on land.

Texture In soils, the fineness or coarseness, which is due to the proportion of sand, silt, and clay particles.

Tillage A critical step in land preparation before crop planting. Tilling incorporates residues and fertilizers, manures, and lime; controls crop pests; provides a seedbed for seeding equipment; and alters the physical conditions and temperature of a soil.

Tiller Secondary stem that grows from the crowns of grasses. These stems have leaf parts and sometimes reproductive parts.

Tilth The beneficial qualities of soil relating to crop plant growth.

Tobacco An herbaceous annual plant belonging to the Solanaceae family that is grown as a drug crop.

Topsoil The A horizon layer of a soil profile. Has the highest fertility and organic matter. Most plant roots and soil organisms grow in this layer.

Toxicity A measurement to describe how toxic or poisonous something is.

Trade name The brand name or name that is used to market an herbicide.

Trans-fatty acids Long-chained fatty acids that have been partially hydrogenated, meaning hydrogen atoms had been added through heat and pressure to produce fatty acids with more saturation.

Transpiration The loss of water from the interior of the leaves of a plant through the stomata.

Triticale A human-made grain species that is the result of crossing wheat and rye. Though it does have high grain protein content, it lacks the breadmaking qualities of wheat and therefore is not widely grown.

Tropical climate Climate characterized by high temperatures, with an average temperature of 64[degrees]F (18[degrees]C) or higher. There is no winter season.

Tropical plant Plant that originated from equatorial regions.

Troposphere The layer of the atmosphere closest to the earth's surface. It extends upwards 8 miles (13 kilometers) high. It contains the greatest concentration of the essential gases for humans and plants. Weather and climate also occur in this layer.

Tuber Enlarged, fleshy, underground stem that stores carbohydrates.

Tuber crop Crop grown for the starches it stores in its tubers.For example, potato.

Tundra A treeless plain in the polar regions.

Turnip A member of the Brassica family grown for its large, fleshy root. It was one of the earliest domesticated crops and can be cooked and consumed much like potatoes.

Under-nutrition A nutritional state where an insufficient number of calories to maintain daily energy requirements are consumed.

United States Department of Agriculture (USDA) The part of the federal government responsible for the administration of federal programs related to farms and rural areas; inspection programs that deal with food and crop production, import, and export; and promotion of research and education in the areas of agriculture and food systems.

Unsaturated fatty acids Long-chained fatty acids that contain at least one double bond between carbon atoms; thus reducing the total number of hydrogen atoms in the molecule. Plants produce these fatty acids, although some fatty acids from plants can be saturated.

Vascular cambium A type of meristem that provides for an increase in stem diameter.

Vegetative The nonreproductive, above-ground portions of plants.

Venation The pattern of veins in a leaf. Part of a plant's vascular system responsible for transportation of water and nutrients.

Vernalization A plant response to winter conditions of cold temperatures and reduced daylight. Important for triggering flowering in the spring.

Vetch Annual legume that produces trailing vines. They are excellent for green manures because they maintain higher nitrogen levels at maturity than other legumes.

Virus A submicroscopic (20-2000 nanometers) pathogen that is made up of nucleic acid and a protein coat. It requires a living host.

Vitamin Micronutrient, typically provided through diet, required by animals for good health.

Warm-season grasses Grasses that have optimum growth when temperatures are near 90[degrees]F (32[degrees]C). Little growth below 50[degrees]F (10[degrees]C).

Water An essential part of life. Humans can survive only days without water. It composes approximately 60% of human bodies and as much as 90% in plants. Chemically, it is described as [H.sub.2]O and can exist as a solid, liquid, or gas.

Water cycle The constant cycle through which the earth's water moves as it goes from solid, liquid, or gas.

Wax A shiny coating that plants produce on leaves and fruit. Protects leaves and the outside of fruit as well as reduces water loss.

Weather The short-term conditions and changes in a region's climate.

Weeds Plants that grow in places where they are unwanted or cause damage.

Wheat An annual small grain that is used to make flour and bread.

White clover A perennial forage legume that spreads by stolons.

Whole grain Products that include the entire grain kernel the bran, germ, and endosperm.

Wild rice A cool-season annual grass grown for its grain. Native to the north central U.S. and central Canada, and sacred to the Native people of those regions. Wild rice grain has high protein and carbohydrate content and low oil content. It is widely used in prepared soups and dry mixes.

Wilted silage Hay crop silage that is dried less than haylage but more than direct cut silage. Typical drying time is between four and eight hours. The moisture content is about 65%.

Winter solstice The shortest day of the year. In the northern hemisphere this is 21 December. In the southern hemisphere it is 21 June.

World population The number of people on the earth.

Xenia effect The immediate effect of one plant's pollen on the endosperm of a different plant's seed.

Xerophyte Plant that can grow in very dry areas because of special features including hairy leaves, thick cuticles, or a small leaf area.

Xylem Part of a plant's vascular system that transports water and minerals from the root system to other plant parts.

Yam A vine that stores energy in tubers. Yams are high in starch and energy and can be consumed directly by humans.

Yield stability In polycultures if one crop dies, the other crop(s) can still produce a yield.

Zenith The point at which the sun is directly overhead. The sun's energy is most intense when it comes closest to the zenith.
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Publication:Introduction to Agronomy, Food, Crops, and Environment
Article Type:Glossary
Geographic Code:1USA
Date:Jan 1, 2009
Previous Article:Appendix 3.

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