Soybean seed requires more water for germination than seeds of many other grain crops; therefore, planting in soils with adequate soil moisture is ideal. In addition to adequate soil moisture, there should be good seed-to-soil contact to ensure adequate water movement into seeds.
Soybean can be established with any tillage-planting (row crop or grain drill) system. It is critical, however, that enough tillage occur to provide a seedbed adequate for proper planter operation. Seed should be placed 1 to 1.25 inches deep. Planting too deep will result in poor emergence. Planters should be adjusted so that the seed depth is as uniform as possible.
Some soils are prone to crusting. If soil forms a crust before beans emerge, break it with a rotary hoe or spike-tooth harrow. Harrow very shallowly.
The preferred row width for full-season beans is 30 inches or less. The yield difference between wide rows (30 inches) and narrow rows (7 inches) is minimal when planting in late April and early May. As the planting date is delayed past mid-May, the yield advantage for narrow rows increases. Planting soybeans with a planter has several advantages in our cropping system. Planters can manage residue better than drills and help to improve emergence rates, reduce slug damage, and reduce the potential for crusting in tilled soils. With improved emergence rates, seeding rates can be reduced with planters. Double-crop beans should be planted in approximately 15-inch rows or less, or as narrow as your equipment allows.
Plant based on seeds per acre rather than pounds of seed per acre. Seed size can vary from 1,800 to 3,000 seeds per pound, with an average about 2,500 per pound.
The optimum plant population for full-season plantings is 100,000 to 125,000 plants per acre. This is increased to 200,000 in double-crop plantings in late June and early July. Seeding rates can be reduced with planters. Check the seeding rate in Table 1.6-1. An alternative method for estimating soybean population is to count the number of plants inside a hoop of varying dimensions. Use the data in Table 1.6-2. 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 and 200,000 plants per acre for double-cropped beans. The seeding rates shown in Table 1.6-1 are adequate for seeding under ideal conditions with seed at 85 percent germination. First, adjust the seeding rates based on germination of the seed. Then, consider increasing the seeding rate by:
- 10 percent for rough seedbeds
- 10 percent for short-season varieties
- 10 percent for cold soils
Similarly, consider decreasing the seeding rate per acre by:
- 10 percent if lodging has been a problem
- 10 percent if planting a lodging-susceptible variety
Some soybean producers are reducing seeding rates because of improved emergence rates and high seed cost. Lower target plant populations of 100,000 to 120,000 plants per acre may be most appropriate for producers who have a history of good soybean emergence rates, low risk of slug damage, good planting equipment, quality seed, and relatively productive soils. Where emergence or average or lower canopy development is possible, reducing soybean seeding rates can pose some risks and result in lower yields. Under these conditions, planting rates of 140,000 seeds per acre can result in sufficient stands for high yields.
To avoid overplanting, calibrate planters carefully. One extra seed per foot of row equates to approximately 75,000 additional seeds per acre when planting in 7-inch rows.
Studies suggest that soybean plants have a tremendous ability to compensate for missing plants. They do this by developing more branches and podding more heavily, overcoming any potential yield loss from missing plants. Reduced yield resulting from poor stands may still be more profitable than replanting a field, which incurs additional costs and means a lower yield potential because of the later planting date.
The optimum date for planting soybean is near that of corn. However, since delayed planting reduces corn yield much more than soybean yield, corn should be planted first. Once corn planting is finished, do not delay soybean planting. Planting in dry, tilled soils can pose some risk for uneven emergence. Waiting for a rain event in these situations can improve emergence, but it can also result in significant planting delays. Eliminating tillage can also help avoid this situation.