Luck versus Skill: Is Nitrogen Balance in Irrigated Maize Fields Driven by Persistent or Random Factors?

The nitrogen (N) balance (i.e., the difference between N inputs and grain N removal) provides an indication of potential N losses to the environment. The magnitude of the N balance in a given year reflects the influence of random (e.g., climate, pest outbreak) and/or persistent (e.g., producer skills, soil type) factors over time. We assessed here the degree to which variation in magnitude of N balance across irrigated maize fields in the US Corn Belt was explained by persistent factors and identified the underlying drivers. Fields with large N balance were identified in specific ("ranking") years, and these same fields were assessed in other ("nonranking") years. Persistent factors explained up to half of the variation in N balance, with 70% of fields with N surplus in a given year also exhibiting surplus in other years. Persistence in large N balance was associated with fields growing maize continuously and applying higher N inputs without any yield advantage compared with other fields. There was also a relationship between N balance and mismatch between producer actual and recommended N rate. These findings highlight available room to reduce N excess in producer fields via improved management, providing a starting point to set priorities and inform policy.