Contribution of Anaerobically Mineralized Nitrogen to the Reliability of Planting or Presidedress Soil Nitrogen Test in Maize

The objective of this work was to evaluate if soil mineralizable N under anaerobic conditions (Nan) improves the reliability of preplant soil nitrate test (PPNT) and presidedress soil nitrate test (PSNT). The study was conducted under no‐tillage (NT) in the southeastern Buenos Aires province, Argentina, in 26 site‐years. In some site‐years treatments were fixed N rates (0, 70, 140, and 210 kg ha −1 or 0, 60, 120, 180, and 240 kg ha −1 ) applied at planting, whereas in others site‐years N rates were determined by adding N to lead targets of N supply up to 120, 160, and 200 kg N ha −1 . When sites were not separated by Nan, relative yield (RY) correlated with PPNT ( r 2 = 0.37) and reliability of PPNT did not increase when sites were separated by low (<48 mg kg −1 ) and high Nan (>48 mg kg −1 ). A high relationship between RY and PSNT ( r 2 = 0.56) was determined. However, when sites were separated by Nan, reliability of PSNT increased, mainly for sites with low Nan ( r 2 = 0.68 and 0.44 for sites with low and high Nan, respectively). Critical PSNT values for 94% of RY were 75 and 90 kg N ha −1 for sites with high and low Nan, respectively. The results show that PSNT was a better diagnostic method for maize ( Zea mays L.) than PPNT. However, the separation of sites by its N mineralization capacity increased reliability of PSNT by indicating a lower N requirement to reach 94% of RY, decreasing the risk of overfertilization, an important feature from economical and environmental standpoints.