Mease (1804) was the first to mention the soybean in the United States literature. He stated, "The soybean bears the climate of Pennsylvania very well. The bean, therefore, ought to be cultivated."
During the past decade, soybean acreage has increased 25 percent per year. However, the acreage is small when compared to the other main agronomic crops grown in Pennsylvania. There are several reasons for this. Soybeans are a cash crop and Pennsylvania farmers traditionally have grown crops that would produce energy and protein for their livestock, rather than crops for cash market. In addition, the absence of available markets has slowed the movement of soybean production outside of southeastern Pennsylvania, where soybean acreage has been the largest.
The situation has changed over the past few years. An increased number of farmers are interested in alternative crops that they can include in their rotations and market as a cash crop. Methods of marketing these crops have evolved for areas outside the major cash crop areas. These factors, coupled with the increasing demand for soybean products, have contributed to the increased interest in this crop.
Soils for soybeans
Generally, soils suited to corn production are well suited to growing soybeans. However, satisfactory results can be obtained on fairly wide range of soils. On finer textured soils, such as clay and clay loam, soybeans respond well where good drainage is present. Yields may be limited on sandy and gravelly soils which tend to dry out during July and August, but soybeans may perform better than corn under these conditions because of their longer flowering period.
Fertilizer needs should be determined from a soil test. The fertilizer rates suggested with soil test results are designed to produce highest economic yields when accompanied by good management.
In general, the soil pH should be maintained in the range of 6.5 to 7.0.
Soybeans need a high level of fertility to produce a good yield. A 50-bushel-per-acre crop of soybeans will remove approximately 40 pounds of phosphate (P2O5) and 80 pounds of potash (K2O). In addition, it uses about 200 pounds of nitrogen which is obtained from nodules on the roots and nitrogen residues in the soil.
It is generally believed that soybeans do not respond to fertilizer applications. This belief arose from the fact that they do not respond to additional fertilizer when a soil test for phosphorus and potassium is in the high-medium to high levels. However, soybeans do respond to fetilizer applications when the soil tests indicate soil levels are low for these nutrients. Fertilizer application is required to build and maintain a soil fertility level satisfactory to good soybean yields. General fertility recommendations are given in The Agronomy Guide.
Soybeans are a legume and will not require the application of chemical nitrogen provided the soil contains adequate amounts of the correct strains of bacteria. If these strains are not present, then the seed must be inoculated with the bacteria prior to planting in order to have good nodulation and nitrogen production.
To get good nodulation requires at least 1,000 viable soybean rhizobia (type of bacteria) per seed at planting. The rhizobia infect the roots and cause nodule formation, where nitrogen is fixed by the bacteria. Rhizobia are introduced by adding soybean inoculant to the seed. Do not use other types of inoculum, such as material intended for alfalfa or clover, since these will not produce nodules on soybeans. The inoculant is available from farm supply stores.
Successful inoculation is a very critical aspect of soybean production in areas and fields that have not grown soybeans in the past. The extra time and effort spent in ensuring proper inoculation will pay in the bin. The following points will help improve nodulation.
- For the first-year beans, apply three times the recommended rate of inoculant. Do not scrimp! Inoculant is inexpensive and too important to cut corners.
- Inoculant contains live rhizobia. Keep the material cool and dry at all times. Keep the packages out of direct sunlight, as high temperatures will rapidly lower the number of live rhizobia.
- Immediately before planting, thoroughly mix, in a tub or bucket, the rhizobia and slightly moistened seed. The seed should take on a black coating of inoculant. Use only a small amount of water to moisten the seed. An excessive amount of water can damage the seed and cause the seed to flow improperly through the planter. Make sure you calibrate the planter with inoculated seed.
Fungicide and insecticide treatments of soybean seed have not given consistent increases in yield. When seed germination is poor (below 80%), and when soil conditions for germination after planting are poor (cold and wet), treatment may increase stands. When soybeans are planted in soils which have not grown soybeans previously, this seed treatment may kill enough inoculant to reduce yields.
If a seed treatment is to be used, it should be applied to the seed several days before the inoculant is added. Several specifically prepared combinations of inoculant and fungicide are commercially available.
A well-prepared seedbed promotes rapid emergence because it provides good seed-to-soil contact and allows more uniform seed placement. Soybeans must absorb 50 percent of their weight in water to germinate. Therefore, good seed-to-soil contact is necessary for rapid germination and emergence.
A corn planter or grain drill can be used to plant soybean seed. When using grain drills, the tension on the disc-openers should be checked carefully so that the seeds are not placed too deep or too shallow. The recommended seeding depth is 1½ inches. Depth bands or other depth control devices are available for most planters. These help ensure proper seeding depth.
Packing after drilling helps ensure better seed-to-soil contact. However, this practice should be avoided because it can cause emergence problems on soils that tend to crust. Using grain drills with press wheels aids in providing good seed-to-soil contact. No-till drills also can be used to establish soybeans successfully.
As mentioned earlier, crusting will cause emergence problems. A rotary hoe or a section harrow should be used to break any crust that develops prior to emergence. These two tools also can be used for early weed control (weeds just emerged).
As with all crops, selecting the right variety is the first step to successful production. The soybean plant is photoperiod sensitive, which means it makes the transition from a vegetative to a reproductive phase in direct response to day length. The key to its flowering mechanism is the length of darkness during a 24-hour period.
Soybean varieties are divided into 12 maturity groups, which form horizontal lines across North and Central America. These groups are (from North to South) 00, 0, I, II, III, IV, V, VI, VII, VIII, IX, and X. Most varieties adaptable to Pennsylvania are in groups II and III. 'Amsoy' is a group II soybean variety and 'Williams' is a group III variety.
Variety tests are conducted at several locations in Pennsylvania each year. Results are published annually and are available from county extension offices. These reports give data on yield, lodging, and seed quality which are important in determining the correct variety. The Agronomy Guide lists the recommended varieties by regions.
The eye cannot detect seed viability; therefore, germination tests are essential. Germination should be above 80 percent. Seeds which are plump, have good color, and are free of damage generally produce good stands.
Soybean seeds need not be broken into pieces to be damaged. Internal injury can occur at harvest and in subsequent handling. Beans dropped from an elevator into a hopper or wagon can receive internal injury. Dropping a bag of seed on the barn floor also can cause internal injury.
Soybean seed can lose viability rapidly when stored improperly and generally cannot be carried over to the next year due to loss of germination.
Buying certified seed each year is the best way to obtain high-quality seed.
Date of planting
Soybeans respond to early planting (Table 1) as do the other major field crops. However, they do not drop in yield as rapidly as corn. For example, corn on average, will decrease yield about 1 bushel/acre/day after May 10 and 1½ to 1¾ bushels/acre/day after May 20. Soybeans will decrease at the rate of 1/3 to ½ bushel/acre/day over the same time span. This is one reason soybeans successfully fit into a corn rotation program. Soybeans normally are planted the last two weeks of May, or after corn planting is finished.
Table 1. Soybean yield response to planting dates*
|Planting Date||Yield (bu/ac)|
|Source: G. J. Ryder, Ohio State University|
*Average over 3 years for four varieties at two locations.
Row width and seeding rates
Seeding rates vary with row spacing (Table 2.) The number of seeds planted per foot of row is based on 85 percent germination and an optimum population of approximately 150,000 plants per acre for full-season beans. This will require between 60 to 90 pounds of seed per acre, depending on seed size. In the past, seeding rate has been described in pounds per acre. However, because of seed size differences between varieties and years, the seeding rate should be determined by the number of seeds per foot of row. This establishes a more consistent plant population.
Table 2. Seeding rates for soybeans
per foot of row*
|*Based on 85 percent germination.|
Highest yields are obtained from narrow (7- to 14 inch) row spacings. (Table 3). Although this has been known for a number of years, it is just becoming accepted by growers. In the past, dependable herbicides have not been available for narrow row culture. Dependable herbicides are available which allow full season weed control without cultivation.
Table 3. Soybean yields for various row spacings
|Source: University of Illinois|
On the average, soybeans planted in 7- to 14 inch rows will yield about 10 percent more beans than those planted in 30-inch rows. Since herbicides are available for full season weed control, growers should capitalize on this yield advantage.
Weed control is an essential part of successful soybean production. The use of herbicides is part of the narrow-row soybean production system. A dependable arsenal of herbicides is available for soybean production. Know the weed problems in the field and select herbicides to control them.
Read and understand the label. When used properly, excellent weed control can be obtained without economic damage to the soybean plants. However, improper application techniques can result in poor weed control and/or serious damage to the soybeans plants.
A rotary hoe or spike harrow can be used for early weed control (weeds just emerged). Be rough on the weeds and do not worry about losing as much as 10 percent of the soybean stand.
Consult the The Agronomy Guide. for the latest recommendations in weed control.
Several factors are involved in a successful soybean harvest. Decisions made at planting time can greatly affect harvesting losses. Soybeans produce pods starting at about 3 to 4 inches above the soil surface and continuing to the top of the plant. A large portion of the pods are on the lower one-half of the plant.
The soil surface should be flat and fairly smooth at the time of planting so that at harvest the cutter bar on the combine can be run as close to the soil surface as possible. Plants in this populations will set pods lower than plants in thicker populations. However, plants in populations that are too thick will lodge excessively. Therefore, planting the correct population will greatly influence the losses encountered at harvest time. Remember that it takes a loss of only four beans per square foot of land area to equal a harvest loss of one bushel per acre.
Approximately 90 percent of the harvest losses occur before the soybeans enter the combine. Soybeans are easy to thresh and clean. The operator must be alert to what is happening at the cutter bar. The combine reel should be operated about 1.25 times the ground speed. If set too fast it will cause excessive shattering and seed loss. The guards should be adjusted properly and the knives kept sharp.
Many problems in harvesting can be overcome by planting on a smooth bed and selecting the correct plant population. During harvest, remember to keep the cutter bar low and the ground speed slow.
The availability of a market should be determined before soybeans are planted. This is a must in areas outside the traditional soybean growing regions. In an area where local businesses are unable to buy the bean crop, they frequently provide space for assembling shipments and filling trucks so the crop can move to a final market. As acreage increases, marketing alternatives may develop in the areas now outside of traditional soybean growing regions.
Prepared by Elwood Hatley, Extension Agronomist; and John O. Yocum, Senior Research Associate. Both are affiliated with The Pennsylvania State University and Extension Service.