If a crop like corn is grown after soybeans and compared to corn-after-corn, the nitrogen requirement is less, and is often referred to as a soybean nitrogen credit. But soybeans do not leave much nitrogen remaining after harvest – either in the residue or in the soil. It is just that soybeans immobilize or tie up less nitrogen than heavy corn stover.
With our more diverse crop rotations this benefit after soybeans does not amount to much. In fact a 50 bu/ac soybean crop provides only a 6 lb N/ac benefit compared to a previous crop of flax. So we do not suggest much of a nitrogen credit following soybeans.
More details please visit MAFRI’s website at: https://www.gov.mb.ca/agriculture/soilwater/nutrient/pdf/fer01s02.pdf