March 1, 2011

Plant Soybeans to the Right Depth

As an agronomist working with corn and soybeans, I’ve walked many miles across fields, assessing plant stands, plant quality and yield potentials. In my travels, I’ve seen a number of subpar fields as a result of improper seeding depth. The trend has mostly been corn that was planted too shallow or soybeans that were planted too deep for soil conditions in the field. I try to follow a simple “2 and 1” rule, which is to plant corn at two inches and soybeans at an inch. Seldom will I vary much from this guideline.
The needs of corn and soybeans are quite different with respect to seeding depth. Corn needs more depth to establish its fibrous network of nodal roots and to construct a proper foundation for a plant that may be towering above by season’s end. Soybeans have a taproot system that penetrates downward immediately following germination. The biggest hurdle for soybeans is to drag the cotyledons (seed leaves) through the soil to sunlight.
Correct planting depth on soybeans is to plant into moisture, but not so deep that the emerging plant has trouble breaking through cold, compacted and crusted soils. If the surface soil is dry, row cleaners can be used to push dry soil to the side and keep the seeding depth close to 1". The sooner the soybean plant is able to emerge without stress, the more vigorous and healthy the plant can be. Planting deep delays emergence, allowing more opportunity for packing rains to crust the soil surface and increase the potential for seedling diseases to damage the stand.
Common mistakes I often see with soybean seeding depth include:
  • Forgetting to reset planting depth from corn to soybeans and vice versa
  • Setting planting depth at the beginning of the season, then not rechecking as the planter is moved to new fields or across differing soil conditions
  • Planting soybeans into fields without consideration of the soil’s potential to crust or to dry out
  • If conditions are exceptionally dry following soybean planting, a roller can be used to firm up the field. Reducing the surface soil’s pore size allows moisture from deeper soil layers to migrate upward and hopefully re-wet the seed zone.
Don’t limit your crop’s yield potential right from the start of the growing season. Take the few extra minutes to check and adjust seeding depth at the start of planting. Look it over again as the planter is moved from field to field.
crusted soil over seedlings

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