Soil-nitrogen, potentially mineralizable-nitrogen, and field condition information marginally improves corn nitrogen management

Anaerobic potentially mineralizable nitrogen (PMN) combined with preplant nitrate test (PPNT) or pre-sidedress nitrate test (PSNT) may improve corn (Zea mays L.) N management. Forty-nine corn N response studies were conducted across the U.S. Midwest to evaluate the capacity of PPNT and PSNT to predict grain yield, N uptake, and economic optimal N rate (EONR) when adjusted by soil sampling depth, soil texture, temperature, PMN, and initial NH₄–N from PMN analysis. Pre-plant soil samples were obtained for PPNT (0- to 30-, 30- to 60-, 60- to 90-cm depths) and PMN (0- to 30-cm depth) before corn planting and N fertilization. In-season soil samples were obtained at the V5 corn development stage for PSNT (0- to 30-, 30- to 60-cm depths) at 0 kg N ha⁻¹ at-planting rate and for PMN when 0 and 180 kg N ha⁻¹ was applied at planting. Grain yield, N uptake, and EONR were best predicted when separating soils by texture or sites by annual growing degree-days and including PMN and initial NH₄–N with either NO₃–N test. Using PSNT (mean R² =.30)-instead of PPNT (mean R² =.19)-based models normally increased predictability of corn agronomic variables by a mean of 11%. Including PMN and initial NH₄–N with PPNT or PSNT only marginally improved predictability of grain yield, N uptake, and EONR (R² increase ≤.33; mean R² =.35). Therefore, including PMN with PPNT or PSNT is not suggested as a tool to improve N fertilizer management in the U.S. Midwest.