Evaluation of Adapt‐N and Realistic Yield Expectation Approaches for Maize Nitrogen Management in North Carolina

Abstract

Core Ideas The North Carolina nitrogen database made better recommendations than Adapt‐N for plot studies. Different labs produce distinctly different soil organic matter percentages from the same soil. Farmer strip trial results demonstrated approximately 60% of the time that Grower‐25% N yielded similarly to the other treatments. Farmer strip trial results showed overall similar performance for Adapt‐N and Grower‐Consultant rates. Nitrogen decision making for maize (Zea mays L.) is difficult because of seasonal weather fluctuations. New tools have emerged based on dynamic simulation models that account for weather variability. We evaluated the performance of the Adapt‐N tool relative to North Carolina's Realistic Yield Expectation (RYE) framework through six multi‐N rate maize plot trials in three physiographic regions and 38 strip trials on commercial farms in the coastal plain. Yield response and profit were evaluated with quadratic plateau (QP) response curves. The RYE framework generally estimated the agronomic optimum N rate (AONR) well, as did Adapt‐N after modification to account for high soil organic matter (SOM) and C/N ratio mineral‐organic coastal plain soil; there was, however, much greater site variability with Adapt‐N. Adapt‐N was sensitive to SOM content inputs, which varied based on method and laboratory. The RYE provided overall higher dollar return than Adapt‐N; Adapt‐N returns varied based on SOM and yield goal inputs, since they strongly impact N rate recommendations. In the on‐farm strip‐trials, 58% of yields were not statistically different between lower N rates and other treatments including Adapt‐N. On average, Adapt‐N performed similar to grower‐consultant practice with modest tradeoffs between reduced N rates and yield. Adapt‐N recommendations and grower rates yielded higher than RYE and required more N. Overall, the RYE approach performed better than Adapt‐N in N research farm trials; in on‐farm strip trials Adapt‐N performed similarly to grower‐consultant practices and in various cases provided economical yield increases over RYE.