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Chapter 15: Putting down our roots.

Although much research remains to be done on the beginning of agriculture, there is already a great deal of interesting knowledge in this area. The most popular theory is that agriculture originated earlier in temperate regions than it did in the tropics. One idea to support this theory is that of need: There was no shortage of food and no need for shelter, clothing, or fire in the tropics, whereas all of these were concerns for those living in colder climates. More evidence for this theory is that the ancestors of many important domesticated crops are from the temperate regions. However, early agriculture in the tropics is difficult to document because the warm, moist conditions are not conducive to the preservation of archaeological remains; thus, we have more evidence from drier, colder regions on which to base our theories. With the diverse climates and soil types major agronomic crops developed in the United States, including: corn, wheat, barley, oats, rice, potatoes, soybeans, cotton, dry beans, peas, peanuts, and alfalfa.

Objectives

After completing this chapter, you should be able to:

* Document the development of agriculture through the ages

*Compare the early humans that survived on hunting and gathering with the twenty-first century hunters and gatherers

* Name the earliest crop plants

* Discuss why certain plants became crops for humans

* Explain and define the three different types of plants

* Describe how the trade routes helped the spread of agriculture crops

* Discuss the major agronomic crops in the United States

Key Terms

slash and burn

Yellow River

wadis

multipurpose plant

mulberry tree

baobab tree

century plant

hemp plant

nitrophiles

taro

irish potato

tuber

cassava

tiller

millets

maize

rye

oats

sorghum

first agriculture revolution

Beginnings of Agriculture

Located in the Fertile Crescent of the Middle East, formed by the Tigris and Euphrates River, the ancient city of Jarmo has been studied by archaeologists, who have documented the existence of agricultural activities there between 10,000 and 12,000 years ago. Jarmo is located in the foothills of the Zagros Mountains, which is now Iraq. Although it is hot and dry today, at the end of the last glacial period climates were cooler and wetter in that area, which made it ideal for agriculture.

Nomadic tribes migrated annually in the fall and winter out of the Zagros foothills to the nearby valleys where forage and water availability lured the animals on which these people depended for meat and hides. These valleys also provided the plants needed for food, fiber, and fuel during the winter; they were not available at the higher elevation of the surrounding mountains.

In the spring, the animals slowly moved back toward the foothills of the mountains and spent the summer in these cooler elevations, where forage was plentiful for the animals as well as for the wandering nomads. This cycle was repeated year after year, and it is probable that the routes and temporary camps used by these nomadic people were the same on each trip. Each such camp had a designated trash dump area in which seeds and roots of the gathered plants were occasionally thrown. The composting of these dump areas produced rich nutrient conditions in which many of the plants sprouted and grew in greater densities than normally found in nature. As the people returned yearly to these areas, they must have gradually realized that using these plants near the campsite was more efficient than wandering far and wide gathering from wild populations. This realization could well have slowly evolved into experimentation by planting increased numbers of selected plants near the camp. Finally, enough food could be grown in such a manner to last year-round, with only occasional hunting forays required to provide meat and hides.

Once these people limited their nomadic activities to one or two semipermanent annual camps and were increasingly dependent on cultivated plants, intensified agricultural activities developed fairly rapidly. Because of reduced hazards associated with a nomadic existence and more leisure time, increasing population size also resulted from this sedentary lifestyle. This further intensified the need for adequate food supplies from cultivation. The domestication of animals followed, until finally villages, such as Jarmo, became firmly established.

In such villages, the evolution from a nomadic existence to a stable one with a stored food supply allowed other advances. With a sedentary existence, material goods could be accumulated, and the potters, weavers, tanners, artisans, and scholars became important members of the community. Advanced civilization rapidly evolved from such beginnings.

The Tehuacan Valley

We now know that agriculture developed independently in other areas of the world at a similar time in history. In the Tehuacan Valley of Mexico, a parallel sequence of events led to an agricultural society dated by archeologists also at 10,000 to 12,000 years ago.

The Tropics

An alternate theory of how agriculture may have first developed centers on the tropical regions of the world. Since this region of the world had ample supplies of water, year-round growing seasons, and warmth, there was less need to cultivate plants. Popularly termed the "genius" theory, this idea holds that since there were abundant food resources, free time was available for other pursuits; greater effort was applied to a consideration of planning, and it follows that the idea to concentrate some of the useful plants of their areas close to the village soon developed. Because of the vegetative density of the tropics, this required clearing some land and planting seeds or underground tubers and rhizomes. Since these areas would revegetate in a normal succession of plant species, a subsequent clearing of new areas every few years was necessary. This has been called the slash and burn technique, and because it allows the balance of nature to be reestablished, it has been a very successful small-scale agricultural practice in the tropics for thousands of years. How many thousands are not known because of the lack of preserved archaeological remains to study and date.

The Yellow River of China runs through a tropical area in which agricultural activities are thought to have existed as long as 15,000 years ago. It is interesting that this area did not develop the complex societies that resulted from agricultural beginnings in the temperate areas of the Middle East and North America (Mexico).

Egypt

Because of the existence of datable archaeological evidence, the Fertile Crescent of the Middle East and the Tehuacan Valley of Mexico have long been accepted as the areas in which agriculture had its earliest beginnings. It is also estimated that agricultural activity was present in the Yellow River area of China 15,000 years ago. But none of these sites has produced evidence as old as that discovered along the Nile River in central and southern Egypt. In this area, some agricultural activity was practiced as early as 18,000 years ago. At that time, the level of the Nile River was much higher than today, and its annual floods provided water to large depressions in the adjacent sand dunes, called wadis. While the water was available, agricultural intensification of wild barley was practiced each year until the heat and lack of rainfall finally dried up the wadis and forced the seasonal farmers back to the more plentiful banks of the Nile. The seminomadic lifestyle apparently continued in this region for 4,000 to 6,000 years but did not result in large, permanent villages, increased population size, or a total dependence on agriculture. Thus, it seems likely that the earliest plant domestication began in areas where agriculture provided only a partial food resource for small hunting and gathering populations. These did not develop into the more complex and advanced cultures that resulted from the separate agricultural beginnings in the Fertile Crescent and the Tehuacan Valley.

Earliest Crop Plants

The period during which people first cultivated part or all of their plant food sources was almost certainly after the most recent glaciation. Cultivation arose independently in several different parts of the world. Until agriculture was used as the primary source of food supply in these early societies, the associated advance of civilization did not develop.

With some certainty, the first plants to be cultivated were those that had been gathered by these societies. We do know that every important civilization depended on cereal crops as the mainstay of their agricultural base. In addition, plants were more likely to have been cultivated if they had many uses or if they were abundant locally and easy to grow.

In the tropical regions the coconut palm (Cocos nucifera), as shown in Figure 15-1, was and still is a very important multipurpose plant.

[FIGURE 15-1 OMITTED]

Its fruit provided plentiful, nutritious, and bacteria-free "milk" and a solid flesh that can be eaten fresh or dried into copra, from which coconut oil can be extracted. The buoyant and watertight outer husks are useful containers, and the fiber of the husk can be made into rope and matting. Palm leaves are used for roof thatching on cottages, which are often constructed using palm trunks for the main supports. In addition, sap from the stem can be fermented into an alcoholic drink or evaporated to produce sugar.

The mulberry tree (Morus) in China provided fruit for human consumption, leaves for silkworms to eat, and a beautiful yellow dye from the wood. In African savanna areas, the baobab tree (Adansonia digitata) is also a multipurpose plant. Its fruits contain seeds rich in oil,

and pulp of the fruit, high in vitamin C and tartaric acid, is made into a popular drink. The leaves have medicinal value, and the trunk provides fiber from which rope can be made. Even the trunks of old baobab trees are hollowed out for water storage during dry periods. The century plant (Agave), as shown in Figure 15-2, of Mexico yields fiber from its leaves and fluids from which several alcoholic drinks, including tequila, are made. Locally the "meat" of the developing flower stalk is a nutritious food source.

[FIGURE 15-2 OMITTED]

One of the best known of the multipurpose plants is the hemp plant (Cannabis). Requiring high levels of nitrogen, this plant might have originally grown along with other weedy nitrophiles. In the nitrogen-rich rubbish piles of the nomadic camps, it was cultivated for fiber from the stems, oil from the seeds, and the medicinal properties of its leaves.

Root and Stem Crops

Because of the ease with which they may be cultivated and because of their high carbohydrate levels, plants with underground storage parts were probably early crop plants. Some of these had roots, and other stems, modified for carbohydrate storage, especially starch. Easily harvested by use of a digging stick, these edible underground parts could well have had their earliest agricultural beginnings in rubbish piles. Deliberate replanting of the leftover pieces of root or stem increased the already abundant food supply for these nomadic people. The use of such root crops in an early form of cultivation almost certainly existed in many different parts of the world.

The taro (Colocasia) from Asia and the similar tannia (Xanthosoma) of the West Indies are both known to have been early root crops. They both have carbohydrate corm--swollen underground stems with stem buds that can each produce a new plant. The Irish potato (Solanum tuberosum) is a modern crop tuber having buds (potato "eyes") that can be planted to produce new plants. Cassava (Manihot utilissima) is another tropical plant valued for its root; tapioca is made from this plant.

Cereals

As food plants, these members of the grass family have several desirable traits. Under cultivation, they yield a large amount of grain per acre, and that grain--the single-seeded fruit--contains carbohydrates, minerals, fats, vitamins, and protein. The grains are compact and dry, which allows for long-term storage, or they can be ground into flour, which also stores well. Additionally, the grass stems (straw) can be woven or thatched into basket, bedding, and housing.

Cereal plants can be encouraged to produce lateral shoots when the upper part of the plant stem is cut off. This process is called tillering and occurs when animals are grazed on young plants. Domestication of grazing animals not only provided these societies with food and skins, but it also increased the density of grain-producing cereal stems (tiller) for harvest.

Cereals do well in plain areas near mountains of semiarid regions. According to archaeological records, millets (Setaria, echinochloa, and Panicum species) were among the earliest cereal crops to have been cultivated in China. However, the crops around which advanced civilizations developed in China and Southeast Asia is rice (Oryza), a cereal plant of the wet lowlands.

[FIGURE 15-3 OMITTED]

In the Middle East, wheat (Triticum) was cultivated in the hilly regions of the Zagros Mountains, and barley (Hordeum) was grown in "upper" (southern) Egypt as early as 18,000 years ago. Both were later introduced into the lower elevations of the river valleys after the development of irrigation techniques. Civilization had then spread from the mountainous highlands to the Tigris-Euphrates and Nile River valleys.

Maize (Zea; Indian corn) is the cereal crop of the Americas, cultivated in the Tehuacan Valley of Mexico at least 8,000 years ago. As in other areas of the world, sophisticated irrigation systems were developed that allowed cultivation to expand and yields to increase. By the time of Christ, chinampas, as seen in Figure 15-3, had been developed. These long, narrow strips of land bordered on three sides by irrigation canals yield several crops per year because there is no need to allow the land to lie fallow for part of each year. The rich muck of the canals is dredged each year and spread on the strips of land, thus, replenishing the topsoil fertility. This maintains the canals while returning the rich nutrients to the soil.

The chinampas system of irrigated agriculture was being practiced by the Mixtecs when the Aztecs conquered the region. The high productivity of this system was a major reason the Aztecs were able to dominate such a large region in such a short period of time. When the Spanish conquistadors arrived in Mexico City in 1519, they found the Aztec emperor was receiving 7,000 tons of corn, 5,000 tons of chilies, 4,000 tons of beans, 3,000 tons of cocoa, 2 million cotton cloaks, and several tons of gold, amber, and other valuables each year from his subjects. All this was possible because of advanced agricultural systems, which include the chinampas.

Other cereal crops that were cultivated include rye (Secale), oats (Avena), and sorghum (Sorghum). Rye was first developed as a secondary crop growing as a weed among the primary crop species. Just as wheat was introduced from the Mediterranean region, so was rye; and since rye does better in colder climates than does wheat, it replaced wheat as the primary cereal crop in such areas and was grown even as far north as the Arctic Circle. Oats probably developed as a major crop plant in a similar way because it is also tolerant of a wide variety of climates. Sorghum is known to have been cultivated in much of Africa, not only for its grain but also for the straw, which was used in the construction of walls and roofs of the village houses and for weaving baskets and sleeping mats. The events discussed in this chapter occurred slowly over hundreds and even several thousands of years. The advent of agriculture, therefore, was truly a slow evolution from nomadic hunting and gathering to a stable society in which the components of civilization could develop.

Because of the much longer period that humans existed as small hunting and gathering groups, maybe as long as 2 million years, the relative suddenness of the beginnings of agriculture are often popularly referred to as the First Agriculture Revolution. Successive advances in agriculture techniques and productions have also been termed revolutions, and in fact a couple of such advances truly were revolutionary.
RESEARCH AND INNOVATION

Until the 19th century, agriculture in the U.S. shared the history
of European and colonial areas and was dependent on European
sources for seed, stocks, livestock, and machinery, such as it was.
That dependency, especially the difficulty in procuring suitable
implements, made American farmers more innovative. They were aided
by the establishment of societies that lobbied for governmental
agencies of agriculture; the voluntary cooperation of farmers
through associations; and the increasing use of various types of
power machinery on the farm. Government policies traditionally
encouraged the growth of land settlement. The Homestead Act of 1862
and the resettlement plans of the 1930s were the important
legislative acts of the 19th and 20th centuries. Also, in 1862, the
drive for agricultural education culminated in the passage of the
Morrill Land Grant College Act.

In the 20th century steam, gasoline, diesel, and electric power
came into wide use. Chemical fertilizers were manufactured in
greatly increased quantities, and soil analysis was widely employed
to determine the elements needed by a particular soil to maintain
or restore its fertility. The loss of soil by erosion was
extensively combated by the use of cover crops, contour plowing,
and strip cropping.

Selective breeding produced improved strains of both farm animals
and crop plants. Hybrids of desirable characteristics were
developed; especially important for food production was the
hybridization of corn in the 1930s. New uses for farm products,
by-products, and wastes were discovered. Standards of quality,
size, and packing were established for various fruits and
vegetables to aid in wholesale marketing. Among the first to be
standardized were apples, citrus fruits, celery, berries, and
tomatoes. Improvements in storage, processing, and transportation
also increased the marketability of farm products. The use of
cold-storage warehouses and refrigerated railroad cars was
supplemented by the introduction of refrigerated trucking, by rapid
delivery by airplane, and by the quick-freeze process of
preservation, in which farm produce is frozen and packaged the same
day that it is picked. Freeze-drying and irradiation have also
reached practical application for many perishable foods.

Scientific methods have been applied to pest control, limiting the
excessive use of insecticides and fungicides and applying more
varied and targeted techniques. New understanding of significant
biological control measures and the emphasis on integrated pest
management have made possible more effective control of certain
kinds of insects.

Chemicals for weed control have become important for a number of
crops, in particular cotton and corn. The increasing use of
chemicals for the control of insects, diseases, and weeds has
brought about additional environmental problems and regulations
that make strong demands on the skill of farm operators. Now
genetic engineering of pest-resistant crops helps overcome the
problems encountered by the use of chemicals.

In the 1990s high-technology farming, including hybrids for wheat,
rice, and other grains, better methods of soil conservation and
irrigation, and the growing use of fertilizers led to increases in
food production, not just in the U.S. but in much of the rest of
the world. U.S. farmers, however, still have the advantage of
superior private and government research facilities to produce and
perfect new technologies.


U.S. Agricultural Crops

The following section covers major agronomic crops of the United States, including: corn, wheat, barley, oats, rice, potatoes, soybeans, cotton, dry beans, peas, peanuts, and alfalfa.

Corn

The botanical name for corn is Zea mays. Worldwide, corn is better known as maize. Several varieties are grown including dent corn,

Successful corn production requires an understanding of the various management practices and environmental conditions affecting crop performance. Planting date, seeding rates, hybrid selection, tillage, fertilization, and pest control all influence corn yield. A crop's response to a given cultural practice is often influenced by one or more other practices. The keys to developing a successful production system include:

* To recognize and understand the types of interactions that occur among production factors, as well as various yield limiting factors.

* To develop management systems that maximize the beneficial aspect of each interaction.

Knowledge of corn growth and development is also essential to use cultural practices more efficiently to obtain higher yields and profits.

Temperature

Corn can survive brief exposures to adverse temperatures--low-end adverse temperatures being around 32[degrees]F and high-end ones being around 112[degrees]F. Growth decreases once temperatures dip to 41[degrees]F or exceed 95[degrees]F. Optimal temperatures for growth vary between day and night, as well as over the entire growing season. The optimal average temperatures for the entire crop growing season, however, range between 68[degrees]F and 73[degrees]F.

Approximately 100 to 150 GDDs (heat units) are required for corn to emerge. Improved seed vigor and seed treatments allow corn seed to survive up to three weeks before emerging if soil conditions are not excessively wet. An early morning soil temperature of 50[degrees]F at the 1/2- to 2-inch depth usually indicates that the soil is warm enough for planting. Corn germinates very slowly at soil temperatures below 50[degrees]F.

Planting hybrids of different maturities reduces damage from diseases and environmental stress at different growth stages (improving the odds of successful pollination) and spreads out harvest time and workload.

The appropriate planting depth varies with soil and weather conditions. For normal conditions, planting corn 1 1/2 to 2 inches deep provides frost protection and allows for adequate root development. Shallower planting often results in poor root development.

Insects of corn include corn earworm, European corn borer, and aphids. Insects are generally controlled by extensive use of insecticides from tassel emergence through kernel drying. Integrated pest management (IPM) using scouting, biological models of pest populations, targeted insecticide use, and narrow-target pesticides have reduced the use of insecticides, improved production profitability, and reduced environmental hazard.

Diseases affecting corn are Southern leaf blight, Northern leaf blight, and diplodia rot. Diseases are controlled primarily through selection of disease-resistant cultivars, good management techniques, and applying appropriate targeted fungicides based upon biological-meteorological models.

Fertilizer requirements vary according to soil tests. A corn crop removes nitrogen, phosphate, potassium, and various micronutrients from the soil. These must be replenished by a fertilization program.

The corn-soybean rotation is by far the most common cropping sequence used in the Midwest. This crop rotation offers several advantages over growing either crop continuously. Benefits to growing corn in rotation with soybean include more weed control options, fewer difficult weed problems, less disease and insect buildup, and less nitrogen fertilizer use.

No-till cropping systems, which leave most of the prior crop residue on the surface, are more likely to succeed on poorly drained soils if corn follows soybeans rather than corn or a small grain, such as wheat. This yield advantage to growing corn following soybean is often much more pronounced when drought occurs during the growing season. Corn is harvested in the fall with a combine. Frequently it has to be dried down before storage.

Wheat

The botanical name for wheat is Triticum spp; however many varieties are available.

Variety Selection

Variety selection should be based on winter hardiness, standability, disease resistance, and yield potential (see Figure 15-4). Although differences in winter hardiness exist among varieties, planting date has the greatest effect on winter survival. The yield potential of available varieties is generally in excess of 150 bushels per acre. This yield is not approached, however, primarily because of a short grain fill period caused by high air temperatures in late June. The ideal air temperature during grain fill is 68[degrees] to 76[degrees]F (20 to 24[degrees]C).

[FIGURE 15-4 OMITTED]

Disease must be controlled if high yields are to be obtained. Both varietal resistance and fungicides are available and may be combined to provide a wide spectrum of protection. Although most available varieties have excellent standability, excessive seeding and nitrogen rates, or their combination, cause lodging, which results in reduced yield.

Because seed size varies from variety to variety and year to year, seeding rates should be based on the number of seeds per foot of row rather than pounds per acre. The ideal seeding rate is 1 million to 1.5 million seeds per acre.

Lodging Control

Lodging is a serious deterrent to high yields. Cultural practices that tend to increase grain yield also increase the likelihood of lodging (when grain falls over to the ground). Using recommended seeding rates, applying proper rates of nitrogen, and selecting lodging-resistant varieties prevents lodging in high-yield environments where yields of 100 bushels per acre are anticipated.

When lodging occurs, the severity of foliar disease increases, resulting in reduced grain yield and quality. Additional effects of lodging are reduced straw quality and slowed harvest. The prevention of lodging increases dividends through a combination of reduced input costs and improved grain and straw quality.

Disease Control

Disease is often the major factor limiting yield of wheat. Effective disease management requires knowledge of the diseases most likely to occur in a production area. Producers fine-tune their disease control strategies for those few diseases encountered each year. Correct diagnosis is the cornerstone to effective control, and producers with little experience identifying diseases should seek help from competent sources, such as a university extension or an agricultural consulting service.

A comprehensive wheat disease management program consists of the following practices:

1. Selecting varieties with resistance to the important diseases in the area. Monitoring wheat diseases aids a producer in selecting varieties with resistance to the common diseases of his or her community.

2. Planting well-cleaned, disease-free seed, treated with a fungicide that controls seeding blights, bunt, and loose smut.

3. Planting in a well-prepared seedbed.

4. Rotating crops--never plant wheat where the previous crop was wheat or spelt. A two- to three-year rotation from wheat prevents most pathogens from surviving in fields.

5. Plowing down residues from heavily diseased fields. Plowing enhances decomposition of residue and death of the disease-causing fungi.

6. Using a well-balanced fertility program based on a soil test. Apply sufficient amounts of phosphorus, nitrogen, and potassium in the fall for vigorous root and seedling growth.

7. Controlling grass weeds. Destroying volunteer wheat, quack grass, and other grass weeds in and around potential wheat fields reduces the amount of disease inoculum available to infect the crop.

8. Applying fungicides only if warranted. Scout fields from flag leaf emergence through flowering. Foliar fungicides are able to control the following diseases: powdery mildew, leaf rust, Septoria tritici leaf blotch, Septoria nodorum leaf, and glume blotch. Leaf rust and powdery mildew are the most severe. Know symptoms, severity ratings, and disease thresholds before scouting fields. Fungicide application following flowering is usually not economical.

Table 15-2 lists some of the common wheat diseases. Seed treatments are an important part of any wheat production system. Seedborne diseases include loose smut, common bunt, and seedborne Septoria and scab. When wheat is planted into a well-prepared seedbed, with good moisture for quick emergence, controlling these diseases and establishing good stands is easy. However, seed treatment cannot compensate for planting in soil that is too wet, too dry, poorly prepared, or for planting at the wrong depth. No-till seeding increases the likelihood of several diseases developing.

Fertilization

Fertilization programs for wheat include consideration of nitrogen, phosphorus, and potassium seeds. Providing adequate nitrogen for the wheat crop is an important step toward high yields. However, as the nitrogen rate increases, the potential for lodging and disease also increases. Depending on the level of soil organic matter, carryover nitrogen from previous crops and yield goal, the amount of fertilizer nitrogen required varies greatly. Small grains respond well to phosphorus fertilizer on soils testing. The small grain response to potassium application is less than that of phosphorus.

Considerations for No-Till Wheat

The successful production of no-till wheat requires the proper management of a different set of inputs than for other crops because wheat must survive the winter while maintaining vigor and fighting disease organisms. Key factors for success include having a smooth seedbed; proper seeding depth, rate, and date; the absence of carryover herbicides; and proper seed treatments and residue management.

Wheat grows well on a range of soils, but does not grow well on poorly drained soil, especially during wet periods. The major cause of stand loss is standing water and the formation of ice sheets where water accumulates. Adequate surface and subsurface drainage is absolutely necessary, and more important for wheat than for other crops. Wheat should not be no-tilled in fields that were wet at the time of the soybean harvest or where soil compaction is present. When planting, grain drills should be adjusted to penetrate crop residue and place the seed one-inch deep.

The severity of several wheat diseases increases when tillage is removed from the production system. Typically, no-till seeding reduces the amount of vegetation produced in the fall. For this reason, and to assure fall tillering, no-till seedings should be made as soon as possible after the fly-safe date. Twenty pounds of starter nitrogen should be applied preplant, along with the other recommended fertilizers, to accelerate root system development and vegetative growth.

The benefits of no-till wheat include reduced production costs and much less stand loss resulting from heaving in spring. Eliminating tillage helps retain soil moisture needed for germination and emergence, and can result in more rapid emergence and better stands when soil moisture is low at seeding.

Barley

The botanical name for barley, which is shown in Figure 15-5, is Hordeum vulgare. Two cultural practices are used to grow barley--winter and spring.

[FIGURE 15-5 OMITTED]

Barley is used mainly for livestock feed. Studies show that ton for ton ground barley may be equal to corn in feeding value for dairy cows when used as 40% to 60% of the grain mixture. It also is sold to the malting industry for use in making beer and other alcoholic beverages. Barley does particularly well when the ripening season is long and cool. Although it can withstand much dry heat, it does not do well in hot humid weather because of the prevalence of diseases under such conditions. It grows better with moderate rather than excessive rainfall. Some spring barley varieties mature earlier than oat, rye, and wheat. Barley can be grown farther north and at higher altitudes than any other cereal.

Barley is one of the most dependable crops in areas where drought, frost, and salt problems occur. It is best adapted to well-drained medium and fine textured soils with a pH of 7 to 8. It generally does not produce satisfactory yields on sandy soils. Barley often lodges when grown on soils high in nitrogen, resulting in low grain yields. Nitrogen management is therefore very important. Barley has the highest tolerance for salts of any of the small grains, but the soils in north central and northeastern Minnesota generally do not have this problem.

Winter Barley

Although barley is an excellent animal feed and easily replaces corn in rations, very little winter barley is grown in colder areas because of a general lack of winter hardiness. If grown, barley should be seeded between September 15 and 30 to increase its chances of surviving the winter. Soil pH between 6.5 and 7.0 and recommended levels of phosphorous will improve winter survival.

Spring Barley

Yield performance of spring barley in some areas has been erratic because of late spring planting due to cool, wet growing conditions, which have delayed maturity. When seeding is accomplished early, fertilization is adequate, and good growing conditions occur, high yields follow.

[FIGURE 15-6 OMITTED]

Bowers

Bowers is an awnless six-rowed barley developed by the Michigan Agricultural Experiment Station and released in 1979. Bowers has exhibited medium-early maturity and medium height. The variety tillers well and usually has large heads. Bowers has exhibited some resistance to a number of barley diseases.

Oats

Figure 15-6 shows the oat plant. The botanical name for oats is Avena sativa.

When used as a companion crop, oat often is removed during early flowering for forage. Oat grain is mostly used as livestock feed with a small amount sold for use in high-protein cereals. Oat grows well on a wide range of soil types, especially if the soil is well-drained and reasonably fertile. Oat is less sensitive than wheat or barley to soil conditions, especially to acidity. Oat generally grows best on medium and fine textured soils, but it also will produce fair yields on light sandy soils if there is sufficient moisture.

The oat plant requires more water for its development than does any other small grain. It also will yield better than the other small grains with less sunshine. Generally, however, oat yields are inferior to those of barley when moisture is a limiting factor. High temperatures during flowering can increase the proportion of empty spikelets, a condition called blast. Hot dry weather during grain fill causes early ripening and reduced yield; hot humid weather during this period favors diseases.

Nitrogen management is important in obtaining the best oat yields. If too much nitrogen is present, lodging can be a problem and yields will suffer as a result.

Several varieties of spring oats with high yield potential, good test weight, and stiff medium-short straw are available. Some varieties are resistant to the common diseases of oats.

Spring oats is the first crop to be planted in the spring. The selection of fields with well-drained soil is essential to permit timely planting. Spring oats should be seeded as early in the spring as soil conditions permit, preferably between March 1 and April 15. Grain yields decrease rapidly as seeding is delayed past mid-April.

Although oats can be established using no-till seeding techniques, little if any crop residue should be present to allow the soil to warm rapidly and the seeds to emerge. Fall preparation of the seedbed eliminates the need for tillage in the spring and sometimes permits earlier planting than when tillage is needed. This technique also eliminates the soil compaction associated with soil preparation.

Soil pH should be above 6.0 unless a legume is also seeded, in which case the soil pH should be 6.5 to 7.0. Phosphate and potash can be applied in the fall or spring. Nitrogen should be applied in the spring anytime before emergence.

[FIGURE 15-7 OMITTED]

Rice

Rice is a member of the grass family. It is an annual monocot. The botanical name for rice is Oryza sativa. Common rice is lowland or paddy rice (requires continuous irrigation or flooded ponding). Upland rice is nonirrigated or not grown in flooded conditions. Wild Rice is not from the same genus and is not related to paddy or upland rice species. Figure 15-7 illustrates the rice plant.

There are 42 rice producing countries in the world, ranging from mountainous Himalayan to lowland delta areas. Rice is the staple food in Asia, Latin America, parts of Africa, and the Middle East.

Within the United States, the rice producing states include: Florida, Arkansas, Louisiana, California, Texas, Mississippi, and Missouri.

Rice thrives under the hot and humid conditions that characterize areas of the southern United States during the summer months. Fields that are nearly level and can be diked and flooded easily are readily adapted to rice production.

Varieties

Rice is divided into short-, medium-, and long-grain varieties, and certain varieties have distinct aromas and flavors. Rice can also be classified according to its cooking characteristics, such as stickiness. Rice is classified into three broad groups by starch and grain characteristics:

1. Waxy or glutinous rice

2. Common, translucent, or nonwaxy rice

3. Aromatic rice

Rice cultivars are characterized by maturity date or length of growing season as follows:

* Very early cultivars--90 days from germination to harvest

* Early cultivars--90 to 97 days

* Intermediate to late cultivars--98 to 105 days

Rice is further classified by cultural adaptation. Japonica is usually short-grained kernels and grown in temperate zones. Indica is usually found in tropical climates, is typically long-grained.

Rice is planted in a level, well-prepared field using a grain drill, which is similar to what is used to plant other small grains. Some rice is seeded with an airplane. Because of Florida's long growing season, rice plants can be harvested and then allowed to regrow for a second harvest or ratoon crop. Approximately half of the rice acreage regrows as a ratoon crop--regrown from young shoots or tillers.

The length of time from planting to harvest is determined by the rice variety and weather conditions. It takes an average of 120 days for the first crop to mature and another 85 days for the ratoon crop to mature.

Weed Control

Weeds are controlled by integrating cultural practices and herbicides. Field preparation includes complete weed removal through disking. Immediately after planting, an herbicide is applied that inhibits weed seed germination or kills growing weeds. As soon as the rice plants reach 5 to 6 inches (13 cm) in height, the flood is applied, which further inhibits weed growth.

Fertilizer

Soil pH needs to be 5.0 to 7.5. Fertilizer needs are determined by a soil test.

Flooding

Rice is an aquatic crop and is flooded during its growing season, this period corresponds with the rainy season in some places like south Florida. Rice fields actually serve as temporary storage for this rainfall and allow for the gradual addition of this water back into the environment.

Rice fields are flooded when the rice plant is about 6 inches high. The flood is maintained 2 to 4 inches deep until the rice grain has matured and begins to dry out. The flood is drained prior to harvest to insure firm ground for harvest equipment. About one month after the harvest operation is complete, the flood is reestablished to allow the ratoon crop to grow.

Paddy leveling and levee building are very critical to maintaining optimum and uniform paddy water depth. Soils must hold water well after flooding. Flooding is used to control some weeds and insect pests but may lead to waterborne disease spread, some water weeds, and some water insect pests. Typically, flooding begins at tillering, although flooding at planting occurs in some instances.

Pests

The fungal disease, blast, is a serious problem for rice growers. The best control available is to plant blast-tolerant varieties, although some fungicide is used in case of high disease incidence. Other diseases of rice include seedling blight, sheath blight, red rice, leaf spot, stem rot, and root rot.

When rice is grown as a rotation crop with sugarcane or vegetables, certain insects such as the rice water weevil have not become a problem. Stinkbugs are a problem and must be controlled. Fields are scouted and, when population thresholds are exceeded, control measures with approved insecticides are started. Stinkbugs pierce the immature kernels with their proboscis and, by sucking the juices, reduce the quality of the seed. Other insect pests include rice water weevil, leafhoppers, thrips, and grasshoppers.

Insect-feeding and wading birds are welcome additions to the rice fields. Blackbirds and bobolinks (small migratory sparrowlike birds) are not. Blackbirds not only pull up the new seedlings and eat the seed but also eat the mature grain. Bobolinks eat large amounts of mature grain just before harvest. Both of these birds can seriously reduce yields.

Harvesting

Once the rice is mature and the fields have been drained, the rice field is harvested with a conventional grain combine. The moisture content of the rice kernel is about 19% at harvest, much too high for quality storage. The first stop for the rice after harvest is the drying bins. There, heated air is forced through the rice until the moisture content has been reduced to 12% to 13%. The rice is then stored in silos until it is milled and sold as white rice.

Potato

The potato is a member of the Solanaceae or nightshade family. It is related to such vegetables as tomato, pepper, and eggplant. It is also related to important drug plants such as datura and belladonna. The potato of world commerce is a tetraploid, which means it has four sets of chromosomes in Solanum tuberosum. Wild potatoes are usually diploid (two sets of chromosomes). This is important for plant breeders who may want to move favorable characteristics, such as disease resistance, from wild populations into commercial cultivars. Other important species of potato are S. andigena, S. phureja, and S. stenotonum.

The potato is a herbaceous dicot that reproduces asexually from tubers, hence the species name tuberosum. The tubers form at the end of underground stems called stolons. The tubers are the edible portion of the plant, and botanically they are stems not roots. They are stems because they contain all the morphological features of stems. They have buds (the eyes), leaf scars (the eyebrows), and lenticels (see Figure 15-8). Lenticels are small pores that allow stems to exchange gases with the air. The tuber is a storage organ. The plant produces sugars in the leaves. These sugars are converted to starch, which is stored in the tubers. The potato then uses the starch to produce new plants the following growing season.

[FIGURE 15-8 OMITTED]

Potato flowers range in color from white to purple and produce small berries that are very poisonous. The berries contain viable seed, but in the past these were not used to produce new potato plants because the offspring were highly variable in such traits as yield and eating quality. The leaves and aboveground stems of the potato plant are also toxic to humans.

The potato is a very versatile crop. It is produced commercially on every continent on Earth, except Antarctica. Potatoes are produced commercially throughout western Europe, but only sporadically in their native range. In the native areas, potatoes are produced mainly for direct consumption. In the United States, potatoes are produced commercially in every state.

The potato is a cool season crop. Mean temperatures in the range of 60[degrees] to 65[degrees]F (6[degrees] to 18[degrees]C) are optimal for high yields. The formation of tubers decreases at soil temperatures above 68[degrees]F (20[degrees]C) and is almost completely inhibited above 84[degrees]F (29[degrees]C). This presents a problem in tropical areas where soil temperatures are usually in this range. A goal of plant breeders is to find potato strains adapted to tropical conditions. Soil temperature is very important in potato growth. Since tuber pieces are planted, this is one of the main determining factors in the growth pattern of the plant. In cool soils, the tubers sprout and emerge slowly. At 52[degrees]F (12[degrees]C) it takes 30 to 35 days for complete emergence. The optimum temperature for emergence is around 72[degrees]F (22[degrees]C). Higher temperatures seem to retard emergence. Soil temperature is also important in determining yield.

The temperate region of the world is ideal for potato production because the plants are started and the tops are established in spring, when temperatures are low. The warm weather of summer causes high rates of photosynthesis, which produces plenty of starch for transport to the tubers. The length of the growing season should be from 90 to 120 frost-free days. In parts of the world where there are shorter growing seasons, potatoes can be grown because the extremely long days of summer compensate.

Both photoperiod and temperature affect tuber initiation (tuberization). In general, short days initiate tubers. For long days, tuberization occurs if night temperatures are well under 68[degrees]F (20[degrees]C). Maximum tuber set occurs when nights are around 54[degrees]F (12[degrees]C). Interestingly, the temperature-sensitive part of the plant is the top and not the stolons or roots.

Low nitrogen levels in the plant favor tuber initiation. This is an important consideration when determining when to make side-dress applications of fertilizer to a potato crop. High light intensity also seems to enhance the tuberization process.

A loose-textured, well-drained soil with a pH of 5.0 to 6.5 is best, but potatoes will grow on almost any soil. Diseases can cause problems on soil that has high clay content. Generally speaking, the soil needs to be about 4 feet deep as this is the depth of rooting of the potato plant. If the soil texture is too "tight" (high in clay), the tubers that form can be misshapened. A total of 18 to 30 inches (500 to 750 mm) of water is needed throughout the entire life of the crop. This can be in the form of rainfall and/or irrigation. Potatoes respond better if the supply of water is uniform throughout the part of the season when the plant is actively growing. Potatoes require about 0.75 inches of water per week.

Potatoes usually require the application of nitrogen (N), phosphorus (P), and potassium (K), fertilizers. The normal method of fertilizer application is to apply half the needed fertilizer prior to planting and half as a side-dress application.

Potatoes are propagated vegetatively in developed countries, including the United States. Seed pieces weighing 1.5 to 2 oz (40 to 60 g) are used. Large potatoes can be cut by hand with a sharp knife, although commercial growers use automated equipment for this procedure. When the potatoes are cut, they need to be kept at 64[degrees] to 70[degrees]F (18[degrees] to 21[degrees]C) and 85% to 90% relative humidity (RH) for several days. This allows the wound to heal, and protects the tuber from soilborne decay. A good dusting with a fungicide is often substituted for this practice. Each piece of the cut tuber must contain an "eye." Since the eye of the potato is actually a bud, this is where the potato sprout will come from. The pieces are planted 2 to 4 inches (5 to 10 cm) deep in beds 30 to 36 inches (76 to 91 cm) apart with 9 to 12 inches (23 to 31 cm) between the seed pieces.

Because potatoes are propagated vegetatively, the use of disease-free planting stock is very important for good potato production. Many virus diseases are passed from insects feeding on the foliage of potato plants. The disease moves through the stem into the tuber. If infected tubers are used as seed, the new plants are also infected with the disease. Certified seed potatoes are grown in cool areas.

True Potato Seed

The benefit of using pieces of tuber as seed is that all individuals planted from that tuber have the same genetic makeup. In essence they are clones. This allows growers to know what to expect when a certain cultivar is planted as far as yield components, and other quality factors. The seed that is produced in potato berries will germinate and grow into a plant with tubers. In the past, however, the yield from these plants has been very variable. Over the last 10 to 15 years, new breeding techniques have been developed that allow for the introduction of high-yield genes into all the progeny that grow from these seeds. This has led to the production of several commercial cultivars that are grown from true botanical potato seed. These cultivars are presently used mostly by home gardeners and professional market gardeners. The development of this technology should aid in the spread of potato production into developing countries, where the nutritional benefits of potatoes are greatly needed.

Pests

The major insect pests of potato include wireworms, white grubs, Colorado potato beetle, aphids, and leaf hoppers. Wireworms and white grubs are important because they feed directly on the tubers, causing injury, which can lead to sites where diseases can enter. Aphids are important in the spread of virus diseases.

The diseases of major importance are early and late blight, fusarium and verticillium wilt, scab, bacterial ring rot, blackleg, and at least 10 viruses. More and more viruses are found every year in different parts of the world.

Weeds are a major problem in potato production. If the potato crop can be kept entirely weed free for the first six weeks after the emergence of the crop, there is very little competition from weeds. The potato plants get large enough that the ground is shaded and very little additional weed growth occurs. Research has shown that there is no benefit in terms of yield from controlling weeds longer than the first six weeks after crop emergence.

Harvesting

As the potato tubers mature, the tops of the plants begin to turn yellow. In areas of early frost in the fall, the potato vines are killed. In most of North America, chemical vine killers are used. After the vines die, tubers are allowed to cure in the ground for several days to one week. This allows the potato skin to "set" by getting a little thicker and more firm. Large commercial growers dig and handle the tubers by machine, as shown in Figure 15-9. Damage to the tubers opens infection ports through which disease can enter, especially bacterial soft rot in storage. Bruising lowers the quality and price received by the grower.

After harvest, the tubers must be hardened before they can be stored for long periods. This is usually done in a period of four to five days at 61[degrees] to 70[degrees]F (16[degrees] to 21[degrees]C) in high humidity. This is usually done by packing houses. Some growers own their own packing houses, but many are owned by brokers. Once the potatoes are cured, they can be packed for immediate consumption, or stored for use later.

For those potatoes that are going to the processor, it is not necessary to cure the tubers after harvest. In some instances, the potato vines are not killed prior to harvest.

[FIGURE 15-9 OMITTED]

Storage

Potatoes can be stored for almost a year under the proper conditions. Very cool temperatures 40[degrees] to 50[degrees]F (4[degrees] to 10[degrees]C) at 90% RH is ideal (see Figure 15-10). The potatoes must be protected from freezing, since this destroys tubers. If temperatures are too low, the starch contained in the tuber is converted to sugars. Then, when the potatoes are cooked, the sugar turns brown. This is especially bad for the processing industry.

Potato tubers must be stored in the dark to prevent greening. The green color is caused by chlorophyll, which is what plants use to trap the sun's energy. But sunlight also causes the production of the alkaloid, solanine. Green potatoes contain solanine. Solanine is a toxic substance and can cause illness in most cases, or death if too much is consumed.

[FIGURE 15-10 OMITTED]

Soybean

The botanical name for the soybean is Glycine max. It is a native of Asia where it was cultivated long before written history. The date of planting has more effect on soybean grain yield than any other production practice. Regardless of planting date, row width, or plant type, the soybean crop should develop a closed canopy (row middles filled in) prior to flowering or by the end of June, whichever comes first. An early canopy results in high yields because more sunlight is intercepted and converted into yield than when row middles do not fill in until late in the growing season.

Adequate, vigorous stands are more difficult to obtain with early planting. Seed treatments, good seed-soil contact, and reduced seeding depths help establish vigorous stands. Herbicide programs must provide weed control for a longer time until the crop is large enough to suppress weed growth through competition.

Most soybean varieties, shown in Figure 15-11, have genetic yield potentials well over 100 bu/A. A variety's adaptability to the environment and production system where it will be used sets the production system yield potential. Varieties should be selected with characteristics that will help them perform well in the cultural system and environment to be used rather than on their yield record alone. Where excessive growth and lodging are problems, varieties that are medium to short in height with good standability should be selected.

[FIGURE 15-11 OMITTED]

Diseases

Phytophthora root rot is a serious soybean disease everywhere soybeans are grown. Varieties are most susceptible in the seedling stage. Susceptible varieties should not be grown in poorly drained soils or on soils known to have a history of the disease. Seed varieties with good field tolerance should be treated with a fungicide that aids in the control of Phytophthora damping off, or the soil may be treated. Resistant varieties should be treated with a seed treatment fungicide to control Phytophthora damping off if they are to be planted in poorly drained soil using reduced or no tillage.

Pythium and Rhizoctonia root rots are also common, and many varieties are susceptible. Damage to plant stands is greatest on poorly drained soils and during seasons of high rainfall. Pythium is controlled by fungicide seed treatments and seedling infections of Rhizoctonia are controlled by seed treatments containing fungicide.

Sclerotinia stem rot may be severe when wet weather occurs during flowering. Some varieties are less susceptible than others, but there is no known resistance. Stem symptoms appear as water-soaked lesions followed by cottony growth and eventually large, black, irregular shaped sclerotia resembling mouse droppings. Wide rows (20 to 30 inches) and reduced seeding rates aid in control by permitting air to move through the canopy to dry plant leaves and the soil surface.

Brown stem rot can severely reduce yield. The fungus enters the plants through the roots and slowly grows upward into the xylem, where it interferes with the flow of water. The disease symptoms develop after flowering and are identified by an internal browning of the stem in August. Foliar symptoms are rare, but the leaves of infected plants may suddenly wilt and dry 20 to 30 days before maturity and remain attached to the plant.

Phomopsis seed rot can be severe when rainfall occurs intermittently during the dry down and harvest. The longer soybeans are in the field after ripening, the greater the incidence of seed rot. Harvesting soon after the soybeans mature (15% to 20% moisture) decreases the amount of seed damage. Use varieties with a range of maturities to allow for a more timely harvest. Yield and grain quality losses are greater when soybeans are not rotated with other crops.

Soybean cyst nematode (SCN) was first found in the southeastern states in the early 1950s. SCN injury is easily confused with other crop production problems, such as nutrient deficiencies, injury from herbicides, soil compaction, or other diseases.

Tillage

A desirable seedbed for soybeans should be smooth enough to permit the planting equipment to place the seed at a uniform depth. The soil particles should be fine enough to assure good seed-soil contact for rapid germination and emergence. The greater the time required for emergence, the greater the time for disease infection and loss of stand.

The freezing and thawing action on clay, silty clay, and silty clay loam soils tilled in the fall or winter to produce stale seedbeds usually have excellent seedbeds for early no-till spring planting. If these soils are tilled when too wet in the spring, a rough cloddy seedbed will result. Also, spring tillage often causes compaction of the soil below depths of 5 inches, which restricts root growth and reduces availability of water and nutrients.

Silt loam soils and those soils with less than 2% organic matter, but with good drainage, tend to have the most desirable seedbed with a late winter or spring tillage system if the soil moisture level is satisfactory for tillage. Where tillage is used, the type and amount has little effect on yield, provided it is adequate to permit the establishment of a uniform stand and Phytophthora root rot is not a problem. This is true for both heavy- and light-textured soils where organic matter contents are 2% to 6%.

Rhizobium Inoculation

If inoculation is necessary, the seed should be inoculated at the time of planting. Commercial inoculants usually contain strains of bacteria that fix nitrogen more rapidly than native strains, but they usually do not survive well from year to year.

Harvesting

Threshing consists of separating the beans from the pods (portion of the plant fruit that encases the soybean seeds). Most soybeans are harvested and threshed simultaneously by modern combines.

Drying is a postharvest phase during which the beans are rapidly dried until they reach the safe moisture level. After threshing, the moisture content of the beans is sometimes too high for good conservation (13% to 15%). The purpose of drying is to lower the moisture content in order to guarantee conditions favorable for storage or for further processing and handling of the product. Drying can be done by allowing warm, dry air to circulate around the beans. Two methods of drying are used, either natural or artificial drying.

Cotton

The botanical name for cotton is Gossypium spp. Of the more than 30 species, only three are of commercial importance. Cotton is a dicot, annual of almost tropical and/or subtropical origin. Its growth range is limited by length of frost-free growing season. It is classified as an agronomic, fiber crop and is grown primarily for its fiber but also its seed meal and seed oil. Figure 15-12 illustrates a mature cotton plant.

[FIGURE 15-12 OMITTED]

The major production areas worldwide are China and the United States. In the United States, production extends from central California to the southeastern U.S. coast (South Carolina) and south to the southern tip of Texas. Estimated annual world production of 80 million bales is produced by 70 countries. U.S. production is approximately 10 million bales per year. Each bale weighs 500 pounds.

Cotton is produced primarily for lint (fibers) from the mature cotton boll, as shown in Figure 15-13. However, the seeds left after lint removal (ginning) are used for seed oil production and as animal feed or feed supplement (cotton meal). Fibers are protuberances on epidermal cells of the ovule seed coat.

[FIGURE 15-13 OMITTED]

Cotton is a highly mechanized crop from planting through harvest through ginning. Originally, the crop required extensive hand labor for weed control, harvesting, and separating lint and seeds.

Cotton is a complete, perfect flower. It is self-fertile and self-pollinating with the aid of wind and insects. Cotton flowers have multiple anthers but a single, fused pistil.

Pests

Resistance to the complex association of fusarium wilt with nematodes is important in fields where the disease is known or suspected to occur. Cotton cultivars are evaluated under field conditions for their reaction to this combination of problems. The cotton rootknot nematode commonly is associated with the wilt disease, but other nematodes may also contribute to the problem. Only cultivars resistant to the complex should be planted in fields known to have nematode or fusarium wilt problems.

Successful weed control is essential for economical cotton production. Weeds compete with cotton for moisture, nutrients, and light. The greatest competition usually occurs early in the growing season. Late-season weeds, while not as competitive as early-season weeds, may interfere with insecticide applications and may cause harvesting difficulties.

Herbicides are the most effective means for controlling weeds in cotton. To be effective, however, herbicides need to be matched with the weed problem. Preplant and/or preemergence applications are important for ensuring that the cotton has the initial competitive advantage over the weeds.

Problem insects include cotton boll weevil, thrips plant bugs, pink bollworm, and budworm. Two major diseases concern cotton growers--damping off from fungi and bacterial blight.

The use of IPM technologies of scouting, introduction of biological controls (predators), targeted or narrow-spectrum pesticides, and use of biological insecticides are reducing the total chemical load and reducing production costs. There is an increasing market for "organic" cotton produced without insecticides.

Diseases are controlled through use of resistant cultivars and proper management practices; for example, sanitation, drainage, and fungicides. Seeds for planting are typically treated with fungicide to prevent seedling diseases.

Chemicals can be used just before or at planting to reduce nematode population densities. However, their use is not always justified. The grower must compare the cost of treatment with the dollar value of the anticipated yield improvement.

Crop rotation can help keep preplant nematode population densities from becoming too high and is important in managing a soilborne fungal disease such as fusarium wilt. Grass family crops, such as small grains, corn, sorghum, millet, and forage grasses are good crops to rotate with cotton because they support few root-knot and reniform nematodes.

Planting occurs after all danger of frost is past and soil temperatures warm 68[degrees] to 77[degrees]F (20[degrees] to 25[degrees]C). Plants do well with high temperatures during growing season. This crop requires high light intensity and ample soil moisture. Cotton needs well-drained, sandy loam soil, and requires high fertilization. The major production limitation is the length of the growing season.

Crop destruction after harvest reduces the levels of pests and pathogens available to attack the following crop. Under some conditions, cotton roots can survive a long time after harvest. Fields should be tilled as soon as possible after harvest to stop reproduction of nematodes and other pests that can live in (or on) cotton roots or stubble, and to allow natural population decline to begin. Nematodes that can damage cotton can build up on weeds and other crops that may precede it, and many other crops can be affected by the nematodes that will build up on cotton. Thus, killing the roots after harvest by plowing them up and exposing them to sunlight is important to prepare for either cotton or a different crop to follow cotton.

Harvesting

Cotton is harvested with a combine and hauled to a gin. At the gin, the cotton is separated from the seed. The cotton is baled into 500 pound bales for further processing. The seed is either sold for livestock feed directly, as shown in Figure 15-14, or the oil may be extracted from it and then sold as cotton seed meal.

[FIGURE 15-14 OMITTED]

[FIGURE 15-15 OMITTED]

Dry Beans

Dry beans are produced in a variety of colors and sizes. The botanical name for beans is Phaseolus spp. The common red kidney bean is Phaseolus vulgaris. Figure 15-15 illustrates the typical bean plant.

The best soil for dry bean production is a loamy soil with high organic matter and good drainage. Fine-textured soils tend to be poorly aerated and susceptible to compaction problems, while coarse-textured sandy soils tend to be droughty and susceptible to wind erosion. The best bean soils are nearly level. Steeper slopes are susceptible to water erosion.

Beans need a frost-free season of 100 to 120 days, with frequent rains or proper irrigation during the period of rapid growth and plant development.

Variety and Seed Selection

Growers select high-quality, disease-free seed. Certified seed is a dependable source of high-quality seed that has passed rigid quality standards. For colored bean types, regardless of the source, growers should have seed tested or ask their seed suppliers for results of disease tests, including common bean mosaic virus and bacterial blight. Regardless of blight test results, all bean seed should be treated with streptomycin sulfate (along with an insecticide and fungicide) to control external bacterial organisms on the seed coat surface.

Planting

Growers plant beans, if possible, following corn, or small grain seeded to a clover green manure crop, or after alfalfa. Planting beans after beans or after beets is not recommended. Producers try to choose fields for beans that are level or only slightly sloping, well-drained, medium to fine textured, with good water-holding capacity. If the field has low spots where water is likely to collect after heavy rains, use a land leveler or construct open shallow surface ditches running to an outlet to lead off excess water.

Where the soil is subject to wind erosion, some growers may seed a small grain (rye is excellent) for winter and early spring cover. They keep it mowed to a 4- to 6-inch (10 to 15 cm) height to prevent excessive moisture loss until fitting and planting. In fine-textured soils, rye can be used to dry out the ground in the spring to allow fitting under optimum moisture conditions. Growers use tillage in fitting the land for beans to avoid soil compaction.

In already compacted soils, deep tillage is recommended. This must be done when the soil moisture content is at an intermediate level.

Soil and Fertilizer

Growers should follow soil test recommendations in using fertilizers. Beans are very sensitive to fertilizer applied in contact with the seed. As a general guide, the micronutrients manganese and zinc may increase yields, particularly under high soil pH. When submitting a soil sample, these micronutrients need to be tested. Beans generally respond to nitrogen.

Planting Practices

Traditionally, the first part of June has been the preferred planting period, if soil moisture is favorable. With the development and release of full season direct-harvest types, a planting period can begin in late May, provided soil temperature [65[degrees]F (18[degrees]C) or higher] and moisture are favorable.

Seeds should be placed at a uniform depth in moist soil. Planting in dry soil or planting deep to reach moisture is not recommended. See Table 15-3 for planting rates for different dry bean classes.

Weed Control

Herbicide should be chosen for the type of weed problem that exists. Growers develop a program for perennial weed control that involves control in nonbean years and some cultivation to hold these weeds down in the year of growing beans.

Diseases

Several serious diseases affect dry edible beans. Some, such as bacterial blight and common bean mosaic virus, are seedborne and can be perpetuated by planting disease-infected seed. Others, such as fusarium root rot and bean rust, are not perpetuated by seed. Table 15-4 lists bean diseases and their control.

Other disease control measures include:

1. Planting disease-resistant varieties, when available, or seed that has been tested for seedborne diseases.

2. Plowing under all bean refuse, preferably in the fall, to reduce the disease inoculum potential from the previous season.

3. Avoiding conditions that favor fusarium root rot and other soilborne diseases. These conditions include poor soil aeration resulting from soil compaction or poor soil drainage, low soil temperatures, and planting where beans were grown the year before.

4. Avoiding working in bean fields when they are wet.

5. Being prepared to apply agricultural chemicals when halo blight is first observed in the field and to navy beans when bean rust is present three or more weeks before plants mature.

Insect Pests

Good management that yields a clean, vigorous stand of beans will assure a minimum of problems with insect control. No special equipment or operations--only those normally used in producing high yields of quality beans--are needed.

Harvesting

Beans are pulled when approximately 90% of the leaves have fallen and the stems and pods have lost all green color. Plants are pulled early in the day when the pods and stems are tough. Weather conditions at harvest time are all-important to determine the best procedure (see Figures 15-16 and 15-17).

[FIGURE 15-16 OMITTED]

[FIGURE 15-17 OMITTED]

Drying and Storage

If beans are harvested with more than 20% to 22% moisture, they can be stored only a few days before spoiling. At moistures of 16% to 18%, beans will store safely several months. For long-term storage, they should be below 15% moisture. Beans can be dried in most commercial grain driers.

Peas

There are many varieties of peas (Pisum sativum). The processing or market will determine variety grown. Peas are a cool season crop, best planted in late summer or early fall, but early spring crops can be successful where temperatures are not hot during late spring. Both bush and vine types are available for both edible pod-type and regular shelling-type peas. Bush peas can be grown in most areas, but vine types need the cooler, moister climate found along the coast. Vine peas produce more and for a longer period, but they require a trellis to climb on. Figure 15-18 shows a typical pea plant.

[FIGURE 15-18 OMITTED]

Soil

Fields should have uniform fertility, soil type, slope, and drainage to get a uniform pea crop. The best soils are silt loams, sandy loams, or clay loams. Peas need a good supply of available soil moisture, but yields may be reduced by overirrigating as well as underirrigating. Peas grown on wet soils develop shallow root systems, which cannot supply the plant's water requirements when the soil dries out later in the season. Root rot is often a problem in wet soils. Determine corrective lime and fertilizer needs by a soil test. Growers adjust pH to 6.5 or higher for maximum yields.

Soil Temperature and Planting

Good germination will occur at 39[degrees] to 57[degrees]F (4[degrees] to 14[degrees]C). The land should be plowed, harrowed and a cultipacker used lightly to ensure a firm seedbed. The land should be level in order to make harvesting more efficient. Plantings may be made as soon as the soil can be worked in the spring. Enation-resistant varieties may be planted throughout the entire planting season. Fresh market peas and edible pod peas may be scheduled on the basis of heat units and by picking requirements for given plantings. In general, April plantings will require about 70 days to harvest, May plantings about 60 days, and June plantings about 55 days.

Fertilizer

Good management practices are essential if optimum fertilizer responses are to be realized. These practices include:

* Use of recommended pea varieties

* Selection of adapted soils

* Weed control

* Disease and insect control

* Good seedbed preparation

* Proper seeding methods

* Timely harvest

Because of the influence of soil type, climatic conditions, and cultural practices, crop response from fertilizer may not always be accurately predicted. Soil test results, field experience, and knowledge of specific crop requirements help determine the nutrients needed and the rate of application. The fertilizer application for vegetable crops should insure adequate levels of all nutrients. Optimum fertilization is essential for top quality and yields. Recommended soil sampling procedures should be followed in order to estimate fertilizer needs.

Weed Control

Growers cultivate as often as necessary when weeds are small. Proper cultivation, field selection, and rotations can reduce or eliminate the need for chemical weed control.

Insect Control

Proper rotations and field selection can minimize problems with insects. Insect pests of peas are described in Table 15-5.

Disease Control

Proper rotations, field selection, sanitation, spacing, fertilizer, and irrigation practices can reduce the risk of many diseases. Fields can be tested for the presence of harmful nematodes. Using seed from reputable seed sources reduces risk from seedborne diseases. Some disease of peas include bacterial blight, stem rot, downy mildew, enation mosaic virus, leaf roll, powdery mildew, root rot, seed rot, and mosaic virus.

Harvesting, Handling, and Storage

The processor determines time of harvest according to a tenderometer reading, the number of other fields ready for harvest, weather, soil conditions, and the processor's need for quality. Generally, yields of shelled peas increase with increasing maturity, but quality decreases. With mobile viners, the crop is cut and swathed into windrows, threshed out by the mobile viners following swathers. Peas must be delivered to the processing plant soon after harvest, especially when the weather is hot, to avoid off-flavors. With the new pod stripping harvesters, no swathing is needed.

Green peas tend to lose part of their sugar content, on which much of their flavor depends, unless they are promptly cooled to near 32[degrees]F (0[degrees]C) and have 90% to 95% RH, after picking. Hydrocooling is the preferred method of precooling. Peas packed in baskets can be hydrocooled from 70[degrees] to 34[degrees]F (21[degrees] to 1[degrees]C) in about 12 minutes when the water temperature is 32[degrees]F (0[degrees]C). Vacuum cooling also is possible, but the peas must be prewet to obtain cooling similar to that by hydrocooling.

After precooling, peas should be packed with crushed ice (top ice) to maintain freshness and turgidity. Adequate use of top ice provides the required high humidity (95%) to prevent wilting. The ideal holding temperature is 32[degrees]F (0[degrees]C). Peas cannot be expected to keep in salable condition for more than one to two weeks even at 32[degrees]F (0[degrees]C) unless packed in crushed ice. With ice, the storage period may be extended perhaps a week. Peas keep better unshelled than shelled. Also, researchers demonstrated that the edible quality of green peas was maintained better when the peas were held in a modified atmosphere of 5% to 7% carbon dioxide at 32[degrees]F (0[degrees]C) than in air for 20 days.

Peanuts

The scientific name for the peanut is Arachis hypogaea. Figure 15-19 shows a typical peanut plant with the pods underground. Peanut yields and quality rise and fall each year based on weather conditions during the growing season. Moisture and temperature are the two weather factors that have the most impact on crop yields.

[FIGURE 15-19 OMITTED]

The germination process begins when soil temperatures are above 60[degrees]F (16[degrees]C) and viable and nondormant seeds absorb about 50% of their weight in water. For practical purposes, soil temperatures need to be above 65[degrees]F (18[degrees]C) for germination to proceed at an acceptable rate. Large-seeded Virginia-type peanuts planted under favorable moisture and temperature conditions will show beginning radicle (root) growth in about 60 hours. If conditions are ideal, sprouting of young seedlings should be visible in seven days for smaller-seeded varieties and ten days for larger-seeded varieties.

Root Growth

The peanut root grows rapidly following germination. The root tip grows downward in the soil through cell division and enlargement. By the time the main shoot breaks through the soil, the tap root will be 5 to 6 inches (13 to 15 cm) deep. Lateral roots develop from the tap root and may be 1 to 2 inches (2.5 to 5 cm) long at seedling emergence. The cotyledons supply the food for early root growth. Once the vegetative tissues are producing a food supply (photosynthate) greater than their needs, some of the food is transported to the roots.

Any condition that subjects peanut roots to stress should be avoided so that adequate root capacity exists to supply the plant with moisture and nutrients. Lack of an adequate and efficient root system may limit yields.

Vegetative Growth

Vegetative growth is slow for the first three to four weeks, as leaf tissue is limited. As leaves develop and fully expand, the capacity for photosynthate production increases and vegetative growth is more rapid. In early growth stages, cool temperatures cause slow growth. As temperatures rise, vegetative growth increases rapidly. Scientists have determined that optimum peanut growth occurs at 86[degrees]F (30[degrees]C). Excessively high [above 95[degrees]F (35[degrees]C)] or low [below 60[degrees]F (16[degrees]C)] temperatures will slow growth.

High temperatures are often accompanied by drought conditions, and vegetative stress can be observed as visible wilting of the plants. Irrigation alleviates the stress of high temperatures or drought.

Other stress factors reduce the photosynthetic efficiency of the plant and limit yields. Leaf or stem diseases, insect infestations, and chemical phytotoxicity may reduce the vegetative surface area, slow photosynthate production, and reduce plant growth.

Reproductive Growth

Peanuts are indeterminate in growth habit. An indeterminate growth habit means that vegetative and reproductive growth occurs simultaneously. The plant must produce enough food to continue vegetative growth, as well as provide food for seed development.

The first flower develops about 30 to 40 days after emergence. Daily flower production is slow for the next two weeks. By mid-July, dozens of flowers may be visible each day on each plant. Temperature [about 86[degrees]F (30[degrees]C)] and moisture must be favorable for flowering to continue at a steady rate. Any environmental stress may interrupt normal flowering.

Pollination and fertilization occur quickly in the flower. If fertilization of the ovule is successful, the peg begins to grow downward. It takes about 10 days for the peg to penetrate into the soil. A week later, the peg tip enlarges and pod and seed development begins. With favorable temperatures, nutrient, and moisture conditions, mature fruit develops in nine to ten weeks, as in the peanut flower in Figure 15-20.

[FIGURE 15-20 OMITTED]

Weather or biotic stresses may interrupt normal flowering and fruit development. High or low temperatures and big differences between day and night temperatures may stop flowering and fruit development. Drought conditions will slow growth. Diseases, insects, or weeds that effectively reduce leaf or root surface area may result in slower maturation.

Variety Selection

Yield and quality are two major factors that influence variety selection. Growers with significant disease or insect history may need to choose a variety with disease or insect resistance. Planting varieties with different genetic pedigrees reduces the risk of crop failure because of adverse weather or unexpected disease and insect epidemics.

Selecting and Managing Soil

Peanuts are best adapted to well-drained, light-colored, sandy loam soils. These soils are loose, friable, and easily tilled with a moderately deep rooting zone for easy penetration by air, water, and roots. A balanced supply of nutrients is needed, as peanuts do not usually respond to direct fertilization.

Soil pH should be in the range of 5.8 to 6.2. Peanuts grown in favorable soil conditions are healthier and more able to withstand climatic and biotic stresses.

On most peanut farms, it is not possible to plant peanuts every year in the most suitable soil types. A grower plans the long-range use of fields considering rotations and disease, insects and weed problems, along with all crops grown on the farm. Maximum income normally results when the best balance between all crop factors is found.

Crop Rotation

A long crop rotation program is essential for efficient peanut production. The peanut plant responds to both the harmful and beneficial effects of other crops grown in the fields. Research shows that long rotations are best for maintaining peanut yields and quality. A three-year rotation with two years of grass-type crops has been effective in reducing nematode and soilborne disease problems and permits better control of many weeds. These crops respond to heavy fertilization but leave adequate residual nutrients for healthy peanut growth.

Growers with a short rotation program can expect a long-term buildup of diseases such as southern stem rot, black root rot, and sclerotinia blight.

Fertilizing

Peanuts respond better to residual soil fertility than to direct fertilizer applications. For this reason, the fertilization practices for the crop immediately preceding peanuts are extremely important. Grass-type crops generally respond well to direct application of fertilizer. Growers can fertilize these crops for maximum yields and, at the same time, build residual fertility for the following crop of peanuts. Peanuts have a deep root system and are able to utilize soil nutrients that reach below the more shallow root zone of the grass-type crops.

The peanut crop is usually produced without applying any fertilizer materials during the production year. If peanut fields need fertilizers, they should be broadcast before land preparation. Fertilizing peanuts requires an understanding of the growth characteristics and nutrient needs of the plant and the ability of the soil to provide these needs.

Growers should inoculate their peanut seed or fields to ensure that adequate levels of rhizobia are present in each field. Commercial inoculants are available that can be added to the seed or put into the furrow with the seed at planting. In-furrow inoculants are available in either granular or liquid form.

Perhaps the most critical element in the production of large-seeded Virginia-type peanuts is calcium. Lack of calcium uptake by peanuts results in "pops" and darkened plumules in the seed. Seeds with dark plumules usually fail to germinate.

Calcium must be available for both vegetative growth and pod growth. Calcium moves upward in the peanut plant but does not move downward. Thus, calcium does not move through the peg to the pod and developing kernel. The peg and developing pod absorb calcium directly, so it must be readily available in the soil solution.

Adequate soil calcium is usually available for good plant growth, but not for pod development or good quality peanuts. It is important to provide calcium in the fruiting zone through gypsum applications.

Each pod must absorb adequate calcium to develop normally. Gypsum is available in three forms--finely ground, granular, and phosphogypsum. Several additional by-product gypsums are now on the market. The by-product materials vary in elemental calcium content. Studies show that all forms of gypsum are effective in supplying needed calcium when used at rates that provide equivalent calcium levels in the fruiting zone.

Land Preparation

Land preparation begins with the disposal or management of the crop residue from the previous crop. In order to promote decomposition during the winter, crop litter should be chopped or shredded and disked lightly. Seeding a cover crop can help reduce soil erosion during the winter months. Applications of lime, phosphorus, and potassium can be applied at this time if needed.

Planting

As a general rule, peanuts should be planted as soon as the risk of a killing frost is over. Varieties require from 150 to 165 days to reach full maturity. Early plantings usually give higher yields, more mature pods, and permit earlier harvesting.

Peanuts should not be planted until the soil temperature at a 4-inch (10 cm) depth is 65[degrees]F (18[degrees]C) or above for three days when measured at noon. The soil should be moist enough for rapid water absorption by the seed. The planter should firm the seedbed so there is good soil-to-seed contact.

Determining Maturity

The best tasting peanut is a mature peanut. Growers must harvest and deliver mature peanuts to the market. Maturity affects flavor, grade, milling quality, and shelf life. Not only do mature peanuts have the quality characteristics that consumers desire, they are worth more to the producer. However, the indeterminate fruiting pattern of peanuts makes it difficult to determine when optimum maturity occurs. The fruiting pattern may vary considerably from year to year, mostly because of different weather conditions.

Heat units or growing degree days have been evaluated as a means of determining maturity. Research shows that 2,600 growing degree days are needed for the earliest varieties to mature.

Disease

A long rotation is the single most powerful disease management tool available to peanut growers. Resistant varieties are usually the least expensive procedure. Proper rotation and variety selection delays or prevents the onset of most serious disease problems. Once diseases become established, expensive chemicals must often be used.

The first step in controlling peanut diseases, which occur in spite of using long rotations and resistant plants, is to correctly identify diseases and how abundant they are. This can be accomplished by scouting the fields each week to monitor disease levels.

The second step is to determine the best control methods for the identified problems. Cultural and chemical controls are usually used in combination for maximum benefit. Cultural control methods such as rotation, resistant varieties, and crop residue destruction have the general effect of reducing the number of disease-causing organisms (pathogens) such as nematodes and fungi.

Pesticides are only useful if cultural practices have not sufficiently reduced pathogen levels below a certain threshold. Thresholds are levels of disease or weather favorable for disease, which represent an economic threat to the crop. Diseases of the peanut plant include: peanut leaf spot, web blotch, and pepper spot.

Alfalfa

Unlike red or white clover, established alfalfa (Medicago sativa) is productive during midsummer except during extreme drought. Alfalfa is a tap-rooted crop and can last five years and longer under proper management. Whether grazed or fed as hay, alfalfa is excellent forage for cattle and horses. Figure 15-21 shows an alfalfa plant just before being cut.

[FIGURE 15-21 OMITTED]

Once established, good management practices are necessary to ensure high yields and stand persistence. These practices include timely cutting at the proper growth stage; control of insects, diseases, and weeds; and replacement of nutrients removed in the forage. Alfalfa has superior forage quality when managed properly. The major problems are getting a stand and keeping it productive.

Site Selection and Soil Fertility

Alfalfa is best adapted to deep, fertile, well-drained soils with a salt pH of 6.0 to 6.5, but it can be grown with conservative management on more marginal soils. On sites that have more moderate drainage, growers should also seed a grass, such as orchard grass or bromegrass, with alfalfa to reduce winter heaving of the alfalfa. The grass acts as a mulch during winter to reduce variations in soil temperature, which cause repeated freezing and thawing. Grasses also help prevent weed invasion by filling in spaces between alfalfa crowns.

Alfalfa requires high levels of fertility for establishment, especially phosphorus. Soil should be tested 6 to 12 months ahead of planting to determine proper amounts of fertilizer and agricultural lime for successful establishment. Soil salt pH should be 6.0 or above, which allows for good nodulation by the plant use. Growers should disk or plow down any needed limestone 6 to 12 months before seeding to give time for it to react in the soil and raise the salt pH.

In no-till seedings, growers should apply needed lime a year in advance, because it cannot be incorporated. After two years of production, the producer should take another soil sample to determine if the soil needs additional limestone or fertilizer. Top-dressing limestone or fertilizer helps maintain production potential and ensures stand longevity.

Adequate available phosphorus is a key to establishing a vigorous stand of alfalfa. Phosphorus stimulates root growth for summer drought resistance, winter survival, and quick spring growth.

Nitrogen and potash are not as important as phosphorus for alfalfa establishment, but they are needed in small amounts. Soil test recommendations normally are used to guide the application of fertilizers.

Variety Selection

Several varieties of alfalfa are available, but a limited number are adapted to certain areas. There is no single "best" variety for a particular location. The most recommended varieties are those that are consistently high yielding, moderately winter hardy, and have moderate or higher resistance to bacterial wilt, phytophthora root rot, and anthracnose.

Establishment

Alfalfa may be frost-seeded, broadcast, no-tilled, or drilled into a prepared seedbed. Growers frost-seed in January or February to allow freezing and thawing to work the seed into the soil. Planting into killed vegetation using no-till techniques or into a prepared seedbed involves less risk of failure and produces denser, more uniform stands than frost-seeding.

Whether planting no-till or into a prepared seedbed, growers should place seed no more than 1/4 inch deep for maximum emergence. With a prepared seedbed, the soil should be very firm to ensure good soil to seed contact. When broadcasting, growers should firm the field with a cultipacker or roller before and after planting. Drills that are capable of precise seed depth control and have press wheels to firm the seedbed are also excellent.

In dry years, getting a firm seedbed is critical for seedling survival. In dry years, seedlings germinate and then die in a loose seedbed because water does not move up to the upper soil layer where the young roots are.

Companion Crop

Alfalfa is often fall-seeded with small grains such as wheat, oats, and barley. Otherwise, alfalfa is broadcast into these crops during winter. The companion crop prevents excessive soil erosion, decreases weed problems, protects young alfalfa seedlings, and provides some early spring forage before the alfalfa becomes productive. Although beneficial, the small grain companion crops also compete for light, water, and soil nutrients. The companion crop should be harvested for hay or silage no later than the boot stage to minimize competition. Alfalfa often provides one hay cutting in late August to early September when seeded with a companion crop.

Seeding Rates and Mixtures

When seeded alone, growers use 15 pounds (7 kg) per acre of certified seed, which is about the equivalent of 13 pounds (6 kg) per acre of pure, live seed (PLS). When seeded with a grass, 10 pounds (4.5 kg) per acre of bulk alfalfa seed (equal to 8 pounds per acre PLS) is sufficient. Seeding rates for grasses in an alfalfa grass mixture are:

* Bromegrass--10 pounds (4.5 kg) bulk (8 pounds PLS) per acre

* Orchard grass--6 pounds (3 kg) bulk (4 pounds PLS) per acre

* Tall fescue--10 pounds (4.5 kg) bulk (8 pounds PLS) per acre

* Reed canary grass--6 pounds (3 kg) bulk (4 pounds PLS) per acre

Seeding a cool-season grass with alfalfa decreases the potential for heaving, reduces weed competition, lessens damage to soil structure by grazing animals, and reduces bloat potential when grazed. The grass will decrease forage quality but will be a major component in the first cutting only.

Growers make decisions about whether to include a grass based on the intended market or use of the alfalfa and on the winter-heaving potential of the site. If intended for dairy use or sale to a cubing plant, growers seed pure alfalfa. For grazing, beef, or horses, growers use an alfalfa-grass mixture. On sites that have a high clay content subject to heaving, alfalfa-grass mixtures are recommended.

Maintaining Alfalfa Stands

Proper management can allow growers to maintain a productive stand of alfalfa for five or more years. An annual fertility program and proper harvesting management are major factors determining stand productivity and longevity. Insects, diseases, and weeds are problems that can reduce yields and length of stand (see Figure 15-22).

[FIGURE 15-22 OMITTED]

Most alfalfa seedings initially have 15 or more plants per square foot. As the stand ages, some plants die and remaining plants spread to occupy the space. Alfalfa-grass mixtures can maintain productivity with only two alfalfa plants per square foot.

Annual Fertilization

Annual applications of phosphorus, potash, boron, and sometimes lime are necessary to maintain vigorous, productive stands. To avoid nutritional deficiencies, producers should apply fertilizer each year according to soil tests. Phosphorus fertilization of established stands keeps plants vigorous so that high yields can be maintained over time.

Potash application improves winter survival of plants and lengthens the productive life of the stand. Alfalfa stands with fewer than three plants per square foot cannot maintain high yields and are often subject to increased weed invasion.

Annual fertilizer recommendations vary according to phosphorus and potassium levels in the soil, but will be close to 15 pounds (7 kg) phosphate and 55 pounds (25 kg) potash per ton of expected yield. Growers can apply fertilizer at any time. A single application following the first cutting or a split application following the first and third cuttings are both good options. Split applications are useful for irrigated alfalfa, for high-yielding alfalfa stands, or when applying high rates of potash.

Growers should include boron in the top-dress fertilizer at a rate of 1 pound of boron per acre per year. Boron is toxic to seedlings, therefore, it should not be applied at seeding.

Producers should soil test every two to three years to make sure that soil salt pH, phosphorus, and potassium levels are adequate. Also, where needed, growers should top-dress additional lime, as needed, to keep the pH above 6.0.

Harvest Management

Stage of maturity at harvest determines hay quality and affects stand life. Forage quality (protein, energy value) declines rapidly as the plant begins to flower. Figure 15-23 illustrates what happens to protein content as the plant reaches different stages of flowering.

[FIGURE 15-23 OMITTED]

For spring-seeded established stands in the seeding year, growers take the first harvest at the mid- to full-bloom stage. Following harvests are made as flowers begin to appear.

For established stands, growers take the first and second cuttings when the plants are just beginning to bloom. For persistence of the stand, the grower may make one or two more harvests. Alfalfa should not be cut or grazed from mid-September to the first of November. This allows the plant to store root reserves for the winter. After November 1, growers can take or graze a fifth cutting if the soil is well drained or a grass is used to help prevent winter heaving. With a four-cut system, a properly fertilized stand can last six or more years.

Harvesting alfalfa in the bud stage produces three to five cuttings of high-quality hay, such as that shown in Figure 15-24. This practice, however, reduces stand life to three or four years.

[FIGURE 15-24 OMITTED]

Alfalfa can be grazed without a loss of stand using small pasture units and high stocking rates. Producers should use enough animals to remove most top growth in less than 6 to 10 days. Animals are turned onto the alfalfa when alfalfa is in the bud stage. After grazing, alfalfa needs to regrow for 30 to 35 days. To reduce the chance of bloating producers, use poloxalene (bloat-inhibitor) blocks. Hungry animals should never be turned onto lush alfalfa pastures.

Pests

The alfalfa weevil and potato leafhopper are the two major pests of alfalfa. Regular monitoring of alfalfa fields is the best way to prevent economic injury from insects. Growers should spray or cut when insect populations reach economic thresholds, not after insect injury symptoms are apparent.

Alfalfa weevil adults lay eggs in the older alfalfa stems in late fall and early spring, and the larva damage mainly the first cutting. Chemical insecticides can be used when 25% of the tips are skeletonized and if there are three or more larvae per stem. Instead of spraying, some growers will cut the alfalfa when it is in the bloom stage, scouting regrowth for signs of damage.

The immature or nymph stage of potato leafhoppers stunts plants and yellows leaves. It also lowers yield and protein content by sucking juices from young upper stems. Leafhopper numbers can be large enough to warrant treatment before significant leaf yellowing occurs. Population thresholds for chemical control vary with plant height.

Weed Control

Weed control in alfalfa begins with establishing a uniform dense stand of alfalfa or alfalfa/grass. Experts recommend a preplant incorporated herbicide for conventional spring seedings of pure alfalfa. If growers want a grass in spring-seeded alfalfa, they plant the alfalfa alone using a preplant herbicide. The grass is drilled into the alfalfa stand the following spring. Numerous diskings during mid- to late summer give adequate control for late summer seedings.

Control of weeds after alfalfa emergence depends on the individual weeds, the stage of growth of the alfalfa, and whether there is a grass with the alfalfa. Several herbicides control weeds in pure stands of alfalfa, but only a few are available for use in alfalfa/grass stands.

Diseases

Alfalfa subject to several diseases, including phytophthora root rot, bacterial wilt, anthracnose and sclerotinia root, and crown rot. The best control is prevention. Growers should choose a variety with a high level of resistance to phytophthora, bacterial wilt, and anthracnose. There is no varietal resistance to sclerotinia.

Sclerotinia is particularly damaging to fall-seeded alfalfa stands south of the Missouri River. The disease has killed seedling stands, and older stands are also subject to damage. Cultural controls include deep tillage of alfalfa residue to bury the inoculum that is formed in the spring on infected alfalfa. A less practical control is to maintain a three- to four-year interval between forage legumes in a rotation. Red and white or ladino clovers are also hosts of sclerotinia and can be a source of inoculum for subsequent alfalfa crops.

Summary

1. Agriculture is documented for the Fertile Crescent region, of what is now the Middle East, to between 10,000 to 15,000 years ago. At a similar period, agriculture was also developed in the Tehuacan Valley of Mexico. One theory explaining the development of domesticated plants is the "need" theory for temperate regions such as these two.

2. Another hypothesis for the origins of agriculture is the "genius theory" for tropical areas. Domestication of plants is believed to have occurred near the mouth of the Yellow River of China approximately 15,000 years ago. Agricultural practices are now documented as far back as 18,000 years ago for middle Egypt. It is thought that era moved with the flood periods of the Nile River.

3. The earliest crop plants were probably multipurpose plants such as palms, mulberry, and hemp. Root crops are undoubtedly another group of early domesticated plants because of their ease of propagation. "Root crops" also included underground stems (tubers) such as potato and the corms of taro and tannia.

4. The food basis of all advanced civilization is a cereal crop such as rice, wheat, corn, barley, or sorghum. Irrigation systems developed in many early agriculture areas, the chinampas of Mexico being among the best known.

5. Increased travel ultimately resulted in crop introductions from one part of the world to another.

6. Major agronomic crops such as corn, wheat, barley, oats, rice, potatoes, soybeans, cotton, dry beans, peas, peanuts, and alfalfa have some very specific growing requirements.

7. Depending on cultural practices, final product, pest problems, and other environmental factors, growers must select the appropriate variety or cultivar.

8. Based on the variety or cultivar selection, growers prepare the seedbed, the fertilization, irrigation, and pest management to maximize the yield from the crop.

9. Much of successful production involves proper timing; for example, timing of planting, timing of irrigation, timing of herbicides and pesticides, and timing of harvesting.

10. Crop rotation is often helpful in controlling disease, insect pests, and nematodes.

11. Integrated pest management (IPM) at some level is always an option.

Something to Think About

1. When did hunting and gathering agriculture start?

2. Name the countries that make up the Fertile Crescent.

3. Where in the Americas was agriculture evolving at the same time it was in the Fertile Crescent?

4. What was the hypothesis for the origin of agriculture evolving in the tropical areas?

5. How far back in history are agricultural practices documented?

6. List the earliest agriculture crop plants.

7. What are the basic food crops of all advanced civilizations?

8. Name the agriculture area best known for its irrigation system.

9. Trace the migration of agriculture crops to other parts of the world.

10. Describe the production of four agronomic crops in the United States.

Suggested Readings

Ciolek, M. T. 1999. Old World Trade Routes (OWTRAD) Project. Canberra-Asian Pacific Research. Retrieved from http://www.ciolek.com/owtrad.html, June 19, 2008.

Connors, J. J., and S. Cordell, Eds. 1995. Soil fertility manual. Tucson, AZ: Potash & Phosphate Institute.

Garofalo, M. 2003. The History of Gardening: A Timeline to the Twentieth Century, Fields of Knowledge. Retrieved from http://www.gardendigest.com/timegl.htm, June 19, 2008.

Hamrick, D. 2003. Ball Redbook, Vol. 2: Crop production. 17th Ed. Batavia, IL: Ball Publishing.

Janick, J., and J. E. Simon, Eds. 1990. Advances in new crops. Portland, Oregon: Timber Press.

Janick, J. and J. E. Simon, Eds. 1993. New crops. New York: John Wiley and Sons.

Janzen, D., and R. Goodland. 1990. Race to save the tropics: Ecology and economics for a sustainable future. Washington, DC: Island Press.

Jones, J. B. Jr. 2002. Agronomic handbook: Management of crops, soils, and their fertility. Boca Raton, FL: CRC Press.

Mazoyer, M., and L. Roudart. 2006. The history of world agriculture: From the Neolithic age to current crisis. New York: Monthly Review Press.

McMahon, M., A. M. Kofranek, and V. E. Rubatzky. 2006. Hartmanns Plant science, 4th ed., Growth, development, and utilization of cultivated plants. Englewood Cliffs, NJ: Prentice Hall Career & Technology.

Simpson, B. B., and M. C. Ogorzaly. 2000. Economic botany: plants in our world. 3rd Ed. New York, NY. McGraw-Hill, Inc.

United States Department of Agriculture. 1953. Plant diseases, the yearbook of agriculture. Washington, DC: United States Department of Agriculture.

United States Department of Agriculture. 1961. Seeds: The yearbook of agriculture. Washington, DC: United States Department of Agriculture.

United States Department of Agriculture. 1992. Economic comparisons of biological and chemical pest control methods in agriculture: An annotated bibliography. Beltsville, MD: USDA.

Vorst, J. J. 1993. Crop production (3rd ed.). Champaign, IL: Stipes Publishing Company.

Internet

Internet sites represent a vast resource of information. The URLs for Web sites can change. Using one of the search engines on the Internet, such as Google, Yahoo!, Ask.com, and MSN Live Search, find more information by searching for these words or phrases: agronomic crop, baobab tree, barley, cassava, century plant, Chinampas, coconut palm, cotton, Fertile Crescent, Agriculture Revolution, hemp, Irish potatoes, Jarmo, maize, millet, multipurpose plant, Nitrophiles, small grains, slash and burn, tannia, taro, wadis, wheat, and Yellow River.
Table 15-1
Botanical Varieties of Corn

Type          Variety      Features

Dent corn     indentata    Primary commercial feed corn; grain
                           yellow or white; kernels form dent on
                           top upon drying.

Flint corn    indurata     Produced primarily for starch.

Flower corn   amylacea     Easily ground and is used for production
                           of cornmeal or corn flour.

Sweet corn    saccharata   Sugary kernels when slightly immature;
                           the horticultural vegetable crop.

Popcorn       praecox      Subform of flint corn with a hard
                           starchy endosperm; moderately high
                           moisture content; fibrous endosperm
                           explodes when heated.

Pod corn      tunicata     Thought to be an ancestor or relative to
                           corn; individual kernels enclosed in
                           husks or pods; not produced commercially.

Table 15-2
Some Common Wheat Diseases and Disorders

Disease or
Disorder                 Symptoms                 Environment

Head scab        Spikelets of head turn     Warm, wet weather during
                 straw colored, glume       flowering period
                 edges with pink spore
                 masses, kernels
                 shriveled white to pink
                 in color

Powdery mildew   Powdery white mold         High humidity, 60
                 growth on leaf surfaces    [degrees]-75[degrees]F,
                                            high nitrogen fertility
                                            and dense stands

Leaf rust        Rusty red pustules         Light rain, heavy dew,
                 scattered over leaf        60[degrees]-77[degrees]
                 surface                    F, 6-8 hour leaf wetness
                                            for germination and
                                            infection

Septoria         Leaf blotches with dark    Wet weather from
tritici leaf     brown borders, gray        mid-April to mid-May, 60
blotch           centers speckled with      [degrees]-68[degrees]F,
                 black fungal bodies        rain 3-4 days a week

Septoria         Lens-shaped chocolate      Wet weather from mid-May
nodorum leaf     brown leaf lesions with    through June, 68
and glume        yellow borders, brown to   [degrees]-80[degrees]F,
blotch           tan blotches on upper      rain 3-4 days each week
                 half of glumes on heads

Tan spot         Lens-shaped, light brown   Moist, cool weather
                 leaf lesions, yellow       during late May and
                 borders                    early June

Cephalosporium   Chlorotic and necrotic     Cold, wet fall and
stripe           interveinal strips         winter with freezing and
                 extending length of        thawing causing root
                 leaf                       damage

Take all         Black, scruffy mold on     Cool, moist soil through
                 lower stems and roots,     October-November and
                 early death of plants      again in April-May

Fusarium         Seedling blight (pre-      Dry, cool soils, drought
root rot         and postemergence)         stress during seed
                 wilted, yellow plants,     filling
                 roots and lower stems
                 with whitish to pinkish
                 mold; root rot plants
                 have brown crowns and
                 lower stems

Barley yellow    Stunted, yellow plants,    Cool, moist seasons
dwarf            leaves with yellowed or
                 reddened leaf tips

Wheat spindle    Discontinuous yellow       Cool, wet fall followed
streak mosaic    streaks oriented           by cool spring weather
                 parallel with tapered      extending through May
                 ends forming chlorotic
                 spindle shapes

Disease or
Disorder                 Control

Head scab        Seed treatment for infected seed;
                 crop rotation; plow down corn
                 residues

Powdery mildew   Resistant varieties; crop rotation;
                 delayed planting; fungicides

Leaf rust        Resistant varieties; balanced
                 fertility; fungicides

Septoria         Seed treatment; plant less
tritici leaf     susceptible varieties; crop
blotch           rotation; balanced fertility;
                 fungicides

Septoria         Seed treatment; plant less
nodorum leaf     susceptible varieties; crop
and glume        rotation; balanced fertility;
blotch           fungicides

Tan spot         Plow down infested residues;
                 crop rotation; balanced fertility;
                 fungicides

Cephalosporium   Crop rotation; bury infested
stripe           residues; control grassy weeds;
                 lime soil to pH 6.0-6.5

Take all         Crop rotation; control weed
                 grasses; balanced fertility; use
                 ammonium forms of N for spring
                 top dress; avoid early planting

Fusarium         Seed treatments for seedling
root rot         blight; delayed planting;
                 balanced fertility; avoid
                 planting after corn

Barley yellow    Delay planting until after the
dwarf            Hessian fly safe date; balanced
                 fertility

Wheat spindle    Resistant varieties
streak mosaic

Table 15-3
Suggested Planting Rates for Field Beans

                                     Seeds/           Approx.
Type               Row width        ft of row       (lbs/acre)

Black turtle         28                4-5              40
Cranberry            28-32             3-4              60
Kidney               28-32             3-4              60
Navy                 28                4-5              40
Pinto                28                4                50
Yellow eye           28-32             4                60

Table 15-4
Field Bean Diseases and Their Controls

Disease                        Spread                 Control

Halo bacterial          Splashing water,        Copper sprays,
blight                  insects, animals,       disease-free seed,
                        seed                    crop rotation, seed
                                                treatment

Common and fuscous      Splashing water,        Disease-free seed,
blight                  insects, animals,       crop rotation, seed
                        seed                    treatment

Common bean mosaic      Aphids                  Disease-free seed
virus

Root rots               Plowing,                Tolerant varieties
                        cultivation, etc.

Bean rust               Windblown spores        Copper and sulfur

Bean anthracnose        Infected seed           Disease-free seed

White mold              Splashing water,        Fungicide sprays
                        wind

Table 15-5
Insect Pests of Peas

Insect                              Description

Loopers (also alfalfa looper)       Slender, dark, olive-green worms
(Autographa californica)            with pale heads and three
                                    distinct dark stripes. Move in a
                                    looping manner.

Celery looper (Anagrapha            Loopers pale green with no
falcifera)                          distinct marking. Adults are
                                    gray, 3/4 inches long with a
                                    white teardrop on both front
                                    wings.

Cutworms and armyworms              Large grown larvae that feed on
                                    seedlings, leaves, and pods.

Grasshoppers (several species)      May cause considerable damage in
                                    years of grasshopper abundance.
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Title Annotation:PART 5: Plants and Society
Publication:Fundamentals of Plant Science
Date:Jan 1, 2009
Words:17511
Previous Article:Chapter 14: Diversity: vascular plants.
Next Article:Chapter 16: Vegetables.
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