With wheat harvest beginning south of I-70, here are some double crop soybean considerations:
1.) Soil moisture and rainfall- Soil moisture and subsequent rainfall are essential to double crop soybean after wheat. When seeds are planted into dry soil, it may take weeks for soybeans to germinate/emerge and only occurs after rainfall (which we saw during the drought of 2012). If possible, adjust planter to place seed in moist soil, but do not plant deeper than 1.5 inches as soil crusting may become problematic.
2.) Relative maturity- As planting is delayed, there is concern about whether late maturing varieties will mature before frost. When planting late, we recommend planting the latest-maturing variety that will reach physiological maturity before the first killing frost. Soybean flowering is triggered by day length. As days get shorter (and nights get longer) after June 21, soybeans are triggered to flower which generally occurs around the first week of July. Later maturing soybeans will put on more vegetative growth before flowering. The table (adapted from the Ohio Agronomy guide) gives relative maturity guidelines for late planted soybeans.
3.) Row spacing and seeding rate- Plant double crop soybean in 7.5-inch row spacing. Canopy closure is necessary to maximize yield of late planted soybeans. If planting during the second half of June, 225,000 to 250,000 seeds per acre is recommended. In early July, 250,000 to 275,000 seeds per acre is recommended.