Prediction of Relative Corn Yield with Soil‐Nitrate Tests under Irrigated Mediterranean Conditions

Abstract

Soil nitrate tests are a useful tool to manage corn (Zea mays L.) N fertilization under rainfed conditions, but the feasibility of using these tests under irrigated Mediterranean conditions has received little attention. The objective of this study was to determine whether the preplant nitrate test (PPNT), pre‐sidedress nitrate test (PSNT), and soil available‐N content test (PPNT or PSNT plus N fertilizer) could accurately predict relative corn yield (RY) under irrigated, high‐yielding conditions. Twenty‐one corn N‐response experiments were conducted in Northeast Spain between 1999 and 2009. The trials were flood‐ or sprinkler‐irrigated. In each trial, three to six N treatments (from 0–300 kg N ha–1) were surface‐applied to corn. Predictions of RY with the soil nitrate tests were low when the two irrigated systems were considered together (R2 < 0.43). However, the available‐N content provided moderately good predictions of RY for the sprinkler‐irrigated fields (R2 = 0.54–0.65) and poor predictions for the flood‐irrigated fields (R2 = 0.17–0.36). The critical soil available‐N content (0–30‐cm soil depth) for maximum RY was established at 193 to 209 kg NO3–N ha–1 (≈46–50 mg kg–1) for sprinkler‐irrigated corn preceded by a cereal crop. These critical available‐N values were lower when corn followed alfalfa and were greater than the critical PSNT levels reported for rainfed conditions in the Midwest and in Argentina (20–30 mg kg–1). The soil available‐N content test could be a useful tool for managing corn N fertilization under sprinkler‐irrigated Mediterranean conditions.