Growing Soybeans ACCORDING to the USDA Agricultural Statistics Service, 63.3 million acres of soybeans were harvested in the United States during 2007. The harvest resulted in 2,585,207,000 bushels. These numbers are so big that they are hard to grasp. What is clear is that soybeans are a very important crop. Objective: Describe practices associated with soybean production. Key Terms: harvest loss inoculation preharvest loss testa Soybean Production Soybeans are grown throughout the Midwest and in the southern United States. However, some cultivars are adapted to the climatic conditions of the northern United States. Soybeans are annual plants grown from seed. SEEDBED PREPARATION AND PLANTING A soybean seed consists of an embryo, two cotyledons, and a seed coat, called a testa. The cotyledons consist of roughly 40 percent proteins, 20 percent oil, and 35 precent carbohydrates. The purpose of the cotyledons is to provide nutrients to the developing embryo during germination. The embryo consists of an epicotyl, hypocotyl, and radicle. Page 1 www.mycaert.com
Soil Soybeans grow best in soils that are high in organic matter and are well-drained. However, soybeans are somewhat tolerant of wet soils. Soybeans grow best in fields with a ph of 5.8 to 7.0. Higher ph increases the availability of many essential and trace elements. Planting Soybean crops are planted in rows, drilled, or broadcast. The average planting rate is 52 pounds per acre. Soybean seeds are usually planted 1 to 1 1/2 inches deep. They may be planted deeper in drier land. Soybean crops yield more in narrow rows than in 30-inch rows. The soybean canopy should completely cover the space between rows at the time of flowering. The shade created reduces the number of weeds. It is difficult to cultivate soybeans grown in narrow rows. Soybeans grown in narrow rows yield more than those grown in wider rows. Soil Temperature Optimal soil temperatures for soybean seed germination are between 68º and 86ºF. Soil temperatures of 55ºF allow germination to occur but at a very slow rate. Once soil temperatures reach 65ºF, the rate of growth quickens. The seeds must also reach 50 to 55 percent seed moisture for the germination process to begin. Therefore, good seed-to-soil contact is essential. Soybean seedlings can be expected to emerge in five to seven days under good conditions. FIGURE 1. One must keep track of how much soybean seed is in a planter to determine how many acres can be planted. (Courtesy, American Soybean Association, St. Louis, Missouri) Quality Seed When planting soybeans, only the highest quality seeds should be planted. Soybean seeds should be free of cracks, broken seeds, weed seeds, and other varieties of seeds. Planting depth, moisture, pests, nutrients, and harvesting issues should also be considered in choosing a soybean variety. FIGURE 2. Soybeans of the highest quality should always be used when planting. Page 2 www.mycaert.com
VARIETY SELECTION Soybeans in the United States are divided into ten maturity groups designated Maturity Group (MG) 000 to MG X. The cultivars in each maturity group are developed for the specific latitude in which they are grown. Each maturity belt runs east to west in the United States, with only about 100 to 150 miles from the north to the south of each belt. The success of a soybean crop is often based on variety selection. Factors to consider when selecting soybean varieties include: yield potential; maturity; growth habit; plant type and height; lodging resistance; seed color, size, and shape; shattering resistance; herbicide, disease, and insect resistance; protein and oil content; and enhanced traits. Soybeans are classified as indeterminate, semi-determinate, or determinate. Many varieties grown in southern regions are determinate in growth. They end vegetative growth when the main stem terminates in a cluster of mature pods. Most varieties for northern regions are indeterminate. They continue to develop leaves while flowers form. One to three pods appear at the terminal apex. Semi-dwarf, determinate varieties grow about 40 to 50 percent as tall as indeterminate varieties. They have good standability and are well suited for solid-seeding or drilled fields. These are commonly grown in the Midwest. GROWTH REQUIREMENTS The climatic conditions for soybean growth are similar to those of corn. Warm weather, sunshine, and moderate rainfall are all preferable. Established soybean plants are more tolerant of light frosts. The minimum number of frost free days is 140. Fertilizer needs vary from field to field and from year to year. In order to ensure proper nutrient application, soil testing is suggested. Precision farming, including global information systems (GIS) and global positioning systems (GPS), combined with soil testing, is an effective way to address nutrient needs. Nitrogen As legumes, soybeans can obtain all the nitrogen needed for growth from root nodule nitrogen-fixing bacteria. Soybeans have a symbiotic relationship with N-fixing bacteria of the species Bradyrhizobium japonicum. The bacteria receive carbohydrates and minerals from the plant and, FIGURE 3. Using GPS is a recommended method of determining fertilizer needs for different sections of a field. (Courtesy, John Deere) Page 3 www.mycaert.com
in return, the bacteria convert nitrogen gas from the atmosphere to ammonium for use by the plant. In some cases it is beneficial to inoculate seed. Inoculation is the mixing of nitrogen-fixing rhizobia bacteria with the seed just before planting. The seed may not need to be inoculated if the field has previously been planted with soybeans. Research has shown that nitrogen fertilizer added to soil provided no increase in yields. In fact, in the presence of the additional nitrogen, the root nodules fixed less nitrogen. Phosphorus Soybean seedlings need relatively large amounts of phosphorus. Maintaining adequate levels of organic material in the soil is the most efficient and economical way to provide phosphorus. The organic matter is also beneficial to the soil microbes that decompose organic matter to release phosphorus and other nutrients. Potassium Fertilization with potassium sulfate (0-0-50) is recommended if the soil is very low in potassium. Fertilizer formulations with chloride should be avoided because the chloride ion can injure soil microbes. Although potassium sulfate is more expensive than potassium chloride, less is needed, and the sulfur is usually beneficial. Moisture Moisture is essential for plant growth. A moisture deficiency during blooming can greatly reduce soybean yield. Blooming begins 6 to 8 weeks after planting, and mature beans are produced after 12 to 15 weeks. DEVELOPMENT STAGES FIGURE 4. Ample rainfall is necessary for efficient soybean growth and yield. Soybean plants go through different stages of growth. The stages are divided into vegetative stages and reproductive stages. Reproductive stages are noted by R1 to R8. Vegetative Stages The vegetative stages begin with the VE stage and go to the V6 stage. VE designates soybean seedling emergence and occurs when cotyledons are visible above the soil. Page 4 www.mycaert.com
VC designates the cotyledon stage and occurs when the unifoliate leaves are fully extended. To determine all other vegetative stages, count the node where the unifoliate leaves are or were attached and continue counting until you reach the uppermost node with a fully developed leaf. A fully developed leaf is one that has a leaf above it with unfolded leaflets. A V2 plant has unfolded leaves on three nodes (1 unifoliate and 2 trifoliolate). At the V3 stage, the soybean plants are about 7 to 9 inches tall, with four nodes and three unfolded leaflets. The V4 stage is described as five nodes and four trifoliolate leaves above the unifoliate. At V5 the plants are about 10 to 12 inches tall, with six nodes of unfolded leaflets. The V5 stage is about one week from R1 or first flower. At the V6 stage, soybeans are from 12 to 14 inches tall and have seven nodes with unfolded leaflets. Reproductive Stages Reproductive stages are designated R1 through R8, which describe flowering (R1 and R2), pod development (R3 and R4), seed development (R5 and R6), and maturity (R7 and R8). At R1, one open flower is found on the main stem. Flowers are produced in clusters at nodes. The flowering progression is generally from the bottom to the top of the plant. Since soybean flowers are self-pollinated, pods begin to develop soon after pollination. At R2, the plant is in full bloom. At this stage the plant has achieved 50 percent of its mature height and node number. An R3 plant has a 3/16-inch-long pod at one of the four uppermost nodes on the main stem with a fully developed leaf. When one of the uppermost nodes has a pod that reaches 3/4-inch long, the plant is in stage R4. The R5 stage has pods with seeds 1/8-inch long in one of the four uppermost nodes on the main stem with a fully developed leaf. When the green seed fills the pod cavity at one of the four uppermost nodes, the plant is in stage R6. At R7, physiological maturity is reached. One pod on the main stem has reached its mature brown or tan color. R8 is the stage of full maturity and 95 percent of the pods have reached their mature color. FIGURE 5. Most of these soybean pods have reached their mature color. Page 5 www.mycaert.com
Flower and Pod Drop Soybean plants can lose as many as 75 percent of their flowers and/or developing pods prematurely. The causes for the drop include water stress, leaf loss, and high temperatures. Stress-induced losses during podding can be partially compensated for by late-developing flowers. PESTS AND DISEASES Like other crops, soybeans have weed, insect, and disease problems. Weeds Weed problems should be handled early so that yield is not reduced. Tilling before planting and when plants are young is one method of weed control. Pre-emergence herbicides are also used to control weeds. The use of genetically modified soybean varieties that can withstand selected herbicides is another method of weed control. Insect Pests Common soybean insect pests include wireworms, white grubs, bean leaf beetles, grasshoppers, Mexican bean beetles, and fall armyworms. Diseases Crop rotation, sound cultural practices, and planting resistant cultivars are ways of avoiding some of the over 50 known soybean diseases. Common soybean FIGURE 6. These soybean plants have become the victim of insect damage. diseases include bacterial blight, bacterial pustule, anthracnose, brown stem rot, Septoria leaf spot, powdery mildew, Phytophthora rot, stem canker, purple seed stain, bud blight, and nematodes. A common nematode problem is the soybean cyst nematode. Symptoms of the soybean cyst nematode are a slight to severe stunting with slight to severe chlorosis. There is a gradual decline of yields over several years as populations increase. There is a decreased nodulation, some root decay may occur, and the canopy is slow to close. Cysts on roots first appear as white, lemon-shaped females on the surface of roots. Cysts turn dark brown with age. Page 6 www.mycaert.com
Pest and Disease Control Cultural, biological, mechanical, and chemical pest control methods may be used individually or in combination to manage pests and diseases. Cultural practices include proper seed selection, planting at the recommended times, amending the soil, and rotating crops. Biological control methods involve the use of natural enemies of a pest to control it. Mechanical control methods involve the use of tools or equipment, such as hoes or plows, to control pests. Chemical control methods involve the use of chemicals, such as poisons, growth regulators, sterilants, and attractants and repellants, to control pests. HARVESTING Most soybeans are harvested once they reach 14 percent moisture. Harvesting is done by combine and begins when the stalks and pods are golden brown, the leaves have fallen from the plant, and the beans are mature. Yields may be estimated before harvest. Harvest loss can also be determined. Harvest Loss FIGURE 7. When soybean plants have reached their final maturity stage, they are ready to be harvested. (Courtesy, AGCO) Harvest loss is loss that occurs as a result of the harvesting process. Harvest loss can be minimized with proper combine adjustment. Operating the combine at an efficient speed will also ensure a maximum harvest yield. Four types of harvest losses are preharvest loss, gathering unit loss, cylinder loss, and separation loss. Preharvest loss is a loss that occurs before harvest begins. It occurs when loose beans or detached pods fall to the ground prior to harvesting. It is also known as preharvest shatter. In order to reduce this loss, soybeans may be harvested before reaching the optimum 14 percent moisture level. Soybeans harvested before they reach 14 percent moisture require artificial drying. Gathering unit loss may be due to shatter loss, stubble loss, lodged stalk loss, or loose stalk loss. Shatter loss occurs when loose beans and detached pods fall during harvesting. Stubble loss results from beans remaining in pods attached to stubble. Lodged stalk loss is a result of beans remaining in pods attached to stalks that were not cut. Loose stalk loss involves beans remaining in pods attached to stalks that were cut but not delivered to the threshing unit. Cylinder loss occurs as beans pass through the combine but remain in the pod. Separation loss occurs as threshed beans are expelled with the trash. Page 7 www.mycaert.com
SOYBEAN PRODUCTION COSTS A soybean enterprise must be profitable in order to justify the costs and efforts to produce a crop. The profitability of a crop can be determined by following a number of steps. The first step is to estimate total soybean yield and expected output price. The estimated yields and prices should be what are expected under normal conditions. The second step is to estimate variable costs. Variable costs are costs that vary with the amount of product produced. These are the out-of-pocket costs that must be incurred if the enterprise is produced or grown. Some examples of variable costs include seed, fertilizer, hired labor, repairs, supplies, and fuel. The third step is to evaluate fixed costs. Fixed costs remain about the same no matter how much is produced. Some examples of fixed costs are insurance, taxes, and depreciation. FIGURE 8. The cost of having fertilizer applied to a field is considered a variable cost. The last step is calculating net receipts. Net receipts represent the income that is left for the farmer and family to live on, pay debt, invest, or save. EXPLORING OUR WORLD SCIENCE CONNECTION: Rhizobium The most important nitrogen-fixing bacterium to the agriculture industry is Rhizobium. Rhizobium bacteria are found naturally in soils. Rhizobia have a special relationship with plants in the legume family, which includes beans, peas, alfalfa, clover, chickpea, and soybeans. Rhizobium bacteria enter the root of a legume through root hairs. They multiply and inhabit cells of the cortex. These cells divide and produce a swelling, called a nodule, on the plant root. It is within the nodules that nitrogen fixation occurs. The presence of the bacteria does not harm the plant. In fact, it is a symbiotic relationship in which both the plant and the Rhizobium benefit. In this relationship, the bacteria receives carbohydrates from the plant and the plant receives a usable form of nitrogen. Seeds of legume crops are often inoculated with Rhizobium bacterium before planting. Inoculation ensures a larger percentage of nodules than what might occur naturally. The result is a crop that exhibits more vigorous growth and greater yields. It also reduces the need for nitrogen fertilizers. Page 8 www.mycaert.com
Estimating Costs and Returns Costs and returns for each acre under production can be estimated. Cost per acre is the total of seed, fertilizer, chemical, drying, interest, equipment, and land costs. Cost per bushel is the cost per acre divided by yield. Return per acre is the quantity of yield times price with cost per acre then subtracted. Return per acre is the amount of money left over to pay for other items not easily accounted for by the contest, such as overhead, utilities, improvements, management, building costs, taxes, and so on. Profitability The profitability of soybeans depends on many factors. Economic factors, such as commodity prices and input costs, are among the most important. Cultural practices, including crop rotation, the selection of varieties well suited for environmental conditions, harvest efficiency, and pest management, play an important role in determining profitability. EQUIPMENT FOR SOYBEAN PRODUCTION The production of soybean crops on a large scale in the United States depends on the use of equipment and technology. Some equipment used in soybean production are tillage implements, planters, cultivators, spray equipment, combines, tractors, storage structures, and GPS equipment. Tillage implements are used for multiple purposes. They are used for seedbed preparation. Tillage equipment is used to incorporate residues, fertilizers, and so on into the soil. Weeds can be controlled with tillage equipment. In some cases, tillage equipment is used to roughen the soil surface to slow the velocity of the wind and, therefore, reduce erosion. Some pieces of equipment used to plant soybean crops are broadcast planters, precision planters, grain drills, and no-till drills. Cultivators come in a variety of shapes, sizes, and attachments. They are used to keep the area between the rows clean and weed free. Spray equipment is typically used to apply chemicals, such as pesticides. FIGURE 9. This soybean field was planted by a no-till drill. Soybean crops can be harvested with a combine. A combine is fitted with a soybean head, which is specifically designed to harvest soybeans. It performs the tasks of harvesting, threshing, and cleaning the grain. Page 9 www.mycaert.com
Farm tractors are used for many purposes, including the pulling of implements and providing power to attachments through the power take-off (PTO). Grain storage structures hold grain until it is ready for market. A Global Positioning System (GPS) provides the farmer with the technological means to practice precision agriculture. Summary: Soybean crops grow best in organic, well-drained soils with a ph of 5.8 to 7.0. They are planted in rows, drilled, or broadcast. Soybean varieties in the United States are divided into ten maturity groups. Many other factors are considered when selecting soybean varieties. The climatic conditions for soybeans are warm weather, sunshine, and moderate rainfall. Soybean plants can obtain all the nitrogen needed for growth from root nodule nitrogen-fixing bacteria. Soybean plants go through vegetative stages and reproductive stages of growth. Soybean crops have weed, insect, nematode, and disease problems. Most soybean crops are harvested once they reach 14 percent moisture. Four types of harvest losses are preharvest loss, gathering unit loss, cylinder loss, and separation loss. The profitability of a crop and costs and returns for each acre under production can be estimated. The profitability of soybeans depends on economic factors and cultural practices. Equipment used in soybean production are tillage implements, planters, cultivators, spray equipment, combines, tractors, storage structures, and GPS equipment. Checking Your Knowledge: 1. What are some seedbed preparation and planting requirements for soybeans? 2. How are soybean varieties selected? 3. What are the nutritional and climatic requirements for soybean production? 4. What are the growth stages of a soybean plant? 5. How are soybean crops harvested? Page 10 www.mycaert.com
Expanding Your Knowledge: Attend a local field day sponsored by a school, extension, or agricultural company to learn more about soybean varieties and recommended production practices. Web Links: Soybean Growth and Development http://www.extension.umn.edu/distribution/cropsystems/components/5701a.html Using Soybean Yield Data to Improve Variety Selection http://www.ianrpubs.unl.edu/epublic/pages/publicationd.jsp?publicationid=132 Planting, Growing and Harvesting Soybeans http://www.nsrl.uiuc.edu/aboutsoy/production02.html Growing Organic Soybeans on CRP Land http://extension.agron.iastate.edu/sustag/resources/soycrp.html Soybean Growth Stage Development http://weedsoft.unl.edu/documents/growthstagesmodule/soybean/soy.htm# Page 11 www.mycaert.com