The approach for determining nitrogen (N) application rates for producing corn has changed, so don't be tempted to subtract a "soybean credit." Current N rate guidelines for corn in Iowa and many nearby states now give suggestions based on specific rotations instead of "crediting" from rates for continuous corn. This means that suggested N rates are those that should be applied for the specific rotation and should not be further modified to account for having a legume in the rotation. In Iowa State University Extension publication Nitrogen Fertilizer Recommendations for Corn in Iowa, PM 1714, for example, a range of 100 to 150 lb N/acre for corn after soybean is recommended. Rates within that range can be adjusted for various site-specific conditions but not for any "soybean credit."
Iowa State University
Sawyer, John E., "Don't double dip soybean" (2007). Integrated Crop Management News. 986.
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