Disentangling Management Factors Influencing Nitrogen Balance in Producer Fields in the Western Corn Belt

CONTEXT: The nitrogen (N) balance provides an indication of the risk for N losses into the environment. Previous studies have shown large variation in N balance among producer maize fields in the US Corn Belt, even within the same region and year. However, little is known about the soil and management factors explaining variation in N balance and to what extent the influence of these factors on N balance occurs via grain yield, N inputs, or both. OBJECTIVE: This study aimed to disentangle interactions among yield, management practices, and soil factors to identify which have the greatest influence on N balance in producer maize fields in Nebraska (USA). METHODS: The database used contains yield and management records from 311 producer irrigated and rainfed fields sown with maize for two years (2010-2011). The N balance was estimated as the difference between N inputs (from fertilizer and applied irrigation) and grain N removal. Random forest regression and path analysis were used to assess the influence of soil and management factors on the N balance via either grain yield or N inputs for irrigated and rainfed fields. RESULTS AND CONCLUSIONS: Analysis based on combination of advanced statistics showed that soil organic matter (SOM), seeding rate, sowing date, and in-season N sidedress influenced N balance, mostly via N inputs application and, to a lesser degree, grain yield. In many cases, producer risk behavior explained the relationship between N balance and soil and management factors. For example, N application was higher in fields that have lower SOM or received in-season N sidedress, without any yield advantage. The findings suggest that efforts are needed to help producers manage N inputs more efficiently and deal with the associated risks. SIGNIFICANCE: Our study performed a novel field level assessment of factors influencing N balance which provides useful information in prioritization of agricultural research and extension programs to avoid large N balances and associated negative environmental impact.