Soybean seed is more sensitive to seeding depth than corn seed. Therefore, achieving the proper soybean planting depth is essential to maintaining high yield potential. Soybean seeding depth surveys conducted in the Midwest have shown that only 20 percent of the fields planted with drills were actually planted at or near the intended depth and that 68 percent were planted too deep.
Under most conditions, soybeans should be planted between 1 and 1.5 inches deep. As a general rule, plant at the shallower end of the range under the following conditions: early planting, high residue conditions, fine-textured soils and moist soils. Planting at the deeper end of the range is recommended under the following conditions: late planting, coarse-textured soils and dry soils. Soybean seed can be planted up to 2 inches deep in sandy soils.
Consider seed size when deciding how deep to plant. Large seed contains more stored energy and can generally emerge from greater depths than small seed. However, the larger cotyledons on large seed are more difficult to pull out of a crusted soil. Plant large soybean seed shallower when planting in soils prone to develop a surface crust.
Never plant soybean seed deeper than 2.5 inches deep as emergence can be reduced by up to 100 percent at this depth. There are three reasons for this:
- The seed cannot provide sufficient energy to lift the cotyledons above the soil.
- The hypocotyl may not be long enough to extend the cotyledons above the soil.
- Soil-borne insects and diseases have more time to damage the seedling.
The first two factors vary by variety. Consult seed company catalogs for emergence ratings before planting deeper than 1.5 inches.
Adequate soil moisture is the most important factor controlling soybean germination. Soybean seed must imbibe 50 percent of its weight in moisture for germination to begin. Germination will be significantly reduced if moisture levels in the seed fall below 20 percent after the seed swells and the seed coat splits. This is why agronomists recommend placing soybean seed into at least 0.5 inches of moist soil at planting. Under dry soil conditions, this may not be possible without planting the seed too deep.
Achieving the proper soybean seeding depth can be challenging when drilling soybeans into untilled cornstalks. The first step is to level the drill from front to back with the front slightly higher than the rear. The next step is to set the planting depth to account for the corn residue. Finally, adjust the down pressure on the openers to cut through the residue and penetrate the soil to the desired depth. Additional weight may need to be added to the frame of the drill under dry or hard soil conditions.
Adjust your soybean planting equipment as soil and crop residue conditions change and dig up seed frequently to verify that it is placed at the intended depth.
This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.