Producing and Harvesting Seeds of Oilseed Crops

J. O. CULBERTSON, H. W. JOHNSON, AND L. G. SCHOENLEBER.

THE LEADING oilseed crops grown in the United States are soybeans, peanuts, flaxseed, safflower, castorbeans, and sesame. A large amount of oil is obtained from cottonseed, but cotton is a fiber crop, and we do not consider it here.

The seeds and oil from them have many uses.

Soybean oil is used in margarine, shortening, paints, varnishes, and other industrial products. Although soybeans are generally classified as an oilseed, the monetary value of the protein, or meal, equals or exceeds that of the oil.

Peanut oil is used for edible purposes.

Nearly all linseed oil from flaxseed goes into the manufacture of paints, varnishes, and linoleum.

Safflower oil is used primarily as a drying oil, but an increasing amount is being consumed in edible products.

The major uses of castor oil are as a drying oil and for hydraulic fluids.

Nearly all the sesame grown in this country is consumed as whole seed.

The harvested acreages of soybeans, peanuts, and flax in the United States in 1960 were about 23.6, 1.5, and 3.3 million acres, respectively.

Safflower acreage has been rising steadily, and about 300 thousand acres were grown in 1960. Castorbean acreage in 1960 was about 30 thousand, and that for sesame, 10 thousand.

The same general cultural practices that produce the best yields of high-quality seed for industrial uses also produce the best seed for planting.

The control of weeds is important in the production of all the oilseeds and is especially important in the production of planting seed. The presence of seed of noxious weeds may cause otherwise good planting seed to be rejected for certification and is sufficient cause for a farmer to refuse to buy uncertified seed. Weeds may also reduce yields and cause difficulties in harvesting. Weed seeds similar in size and weight to the harvested oilseed make further cleaning difficult and expensive.

Chemical weed control has given excellent results with flax and appears promising with peanuts, safflower, sesame, and soybeans. Current recommendations about materials and rates should be obtained locally.

Special aspects, if any, of final preparation of the seedbed are discussed for specific crops in the following sections. It is assumed that basic procedures of early seedbed preparation will be followed before the final preparation.

All oilseed crops are normally self-pollinated, but enough natural cross-pollination occurs to be troublesome when different varieties are grown close together. Safe distances between different varieties vary with the crop.

The isolation of fields intended for seed is treated in a later chapter.

THE LENGTH of days and nights is the primary factor in the flowering and maturing of soybeans.

Each variety has rather specific photoperiod requirements for flowering. Varieties are adapted to the photo-periods of rather narrow latitudinal belts running east and west. A variety grown north of its area of adaptation flowers and matures too late. One grown too far south flowers and matures too early. The most successful production is normally obtained from varieties that utilize the full growing season but mature before frost.

Soybeans do best on fertile, well-drained soils, but they are tolerant of a wide range of soil conditions. They are highly susceptible to salt damage in saline soils. Soil conditions determine their need for fertilizer and lime. Soybeans require relatively large amounts of phosphorus, potassium, and calcium and a pH of about 6.0 for maximum yields.

The soybean, a legume, can be produced successfully without nitrogen fertilizers if it is properly nodulated. Planting seed should be inoculated unless the bacteria are known to be present in the soil. Some growers inoculate the seed every year. Others do not inoculate seed if a well-nodulated crop has been grown on the field within the previous 4 or 5 years. Inoculum prepared specifically for soybeans should be used. It can be applied following chemical treatment of the seed.

Soybeans are normally planted, cultivated, and harvested with equipment used in the production of other crops. The primary consideration in preparation of the seedbed is that weeds should be destroyed immediately before planting.

Most soybeans in the United States are planted in May or June in rows 36-42 inches apart at a rate of about one viable seed per inch of row (40-60 pounds to the acre). Row spacings of less than 36 inches often give increased yields in northern areas; the amount of the increase depends on variety, location, and growing conditions.

Planters should be fitted with soybean plates to prevent serious injury to the seed.

Cultivation with a rotary hoe, drag harrow, or similar implement should begin as soon after complete emergence as necessary to control weeds. Subsequent cultivation may be done with row cultivating equipment.

All seeds on a soybean plant mature at about the same time. At the time the seed matures, leaves soon drop off and the stems dry. The final maturing process is so rapid that chemicals applied early enough to hasten the harvest date reduce the yield.

Harvesting is done with a combine harvester. The moisture in the seed should be 14 percent or less, unless the seed is to be dried artificially.

Mechanical injury increases as the moisture content of the seed drops.

goes seed moisture goes below 10 percent, cracking of the seedcoat and injury to the embryo are more likely to occur in threshing.

Moisture content of seeds and pods may change enough during the day to necessitate adjustments in the speed of the combine cylinder. Cylinder speed should be just fast enough for proper threshing action.

Soybean seed should be combined as soon after maturity as possible to reduce chances of weather damage. Rain and high temperatures after maturity cause rapid deterioration in quality of the seed. Some varieties withstand such conditions better than others, but long periods of warm, rainy weather will damage the seed of all.

Several seedborne diseases affect soybeans, but none need be of serious concern to the seed producer. They are so widespread in the established production areas of the United States that there is little likelihood of seriously increasing their distribution on seeds.

PEANUTS grow their seeds underground. Light-textured soils that do not bake are best. Large amounts of nitrogen, potash, or organic matter are unfavorable. Peanuts grow best on soils with a pH of 6.0 to 6.5 if enough lime is available for normal development.

Peanuts should be planted in a deep, firm seedbed when the soil is thoroughly warm. Planting machines that have seed boxes using slow-moving slant plates and seed cells of the proper size should be used to reduce injury to the tender seeds and seedcoats.

Recommended planting rates range from 35 pounds an acre for small-seeded varieties planted in 36-inch rows to 96 pounds an acre for large-seeded varieties planted in 24-inch rows.

Proper disposal of debris from previous crops before planting operations and careful cultivation to prevent covering leaves, stems, or plants help reduce the incidence of stem rot and enhance yields. Some hand hoeing may be required to remove weeds near the plants.

Numerous diseases and several nematodes may attack peanuts, but relatively few are likely to be serious. They include seedling diseases; heat canker; leaf spot; southern blight; various root, peg, pod, and seed rots; black pod; and concealed damage within the seed.

Two vital factors in sections where peanuts are widely grown are an adequate (but not excessive) supply of soil moisture from the onset of heavy flowering until about 2 weeks before digging, and a generous supply of readily available calcium in the top 3 or 4 inches of the soil where the pods are developing.

Without enough calcium in the fruiting zone of the soil, the seeds may abort, or their development may be impaired at any stage until shortly before full maturity.

Drought accentuates the adverse effects of calcium deficiency in the fruiting zone on seed development. Large.. seeded varieties seem to be harmed more by such a deficiency than those, with smaller seeds.

Two-thirds of the peanut crop now is cured in the windrow for several days to 2 weeks or longer. The rates at which peanuts dry or cure in different positions in the windrow vary. During warm, sunny periods, seeds in pods that are exposed to direct sunlight may dry too rapidly, become hard, have impaired viability, lose their seedcoats, and have a high percentage of breakage on shelling. Seed pods at the bottom of the windrow may become overrun with molds in warm and rainy weather.

The seed peanuts of the highest quality are cured slowly in moderate to cool temperatures. Curing in carefully constructed stacks usually can be expected to give better seed peanuts than curing in windrows.

Harvesting peanuts to insure seed of high quality begins with digging operations. Proper digging, shaking, and loose windrowing to remove all soil from the vines help provide the uniform drying conditions essential for satisfactory combining.

The peanuts should be picked carefully with the picker or combine, which should be operated at the slowest feasible rate. The plants should be fed into the machine at a uniformly moderate rate. With proper adjustments, the recently developed combination carding-cylinder-stemmer combines harvest properly cured, windrowed peanuts with little damage to the seed.

Peanut seeds are among the most delicate that the grower handles. The shelling operation is a violent one. Few seeds come through it uninjured; 2 to 15 percent of the seed may be split in shelling. Others will have ruptured seedcoats, and one or both of the cotyledons may be partly broken away from the embryonic axis. Pieces of the cotyledons of some are broken off. Those that appear to have seedcoats intact often are bruised.