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.
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We would like to thank DuPont Pioneer for funding this research. The authors thank the supporting scientists (Matt Yost; Dan Barker, IA; Lakesh Sharma, Amitava Chatterjee, and Norm Cattanach, ND; Todd Andraski, WI; and Tim Hart, DuPont Pioneer), graduate students (Curtis Ransom and Gregory Bean, MO; Christopher Bandura, WI; and Matt Shafer, IN), field technicians (Matt Volkmann, MO; Jason Niekamp and Joshua Vonk, IL; Glen Slater, NE; Andrew Scobbie, Thor Sellie, Nicholas Severson, Darby Martin, and Erik Joerres, MN), and cooperating farmers and research farm personnel for their help in completing this project. Mention of trade names or commercial products in this publication is solely for the purpose of providing information and does not imply recommendation or endorsement by the affiliated universities or the U.S. Department of Agriculture.