Identification of Nitrogen Management Strategies in Indiana, USA That Impact Corn Stalk Nitrate Concentrations.

Nitrogen management in corn production systems is challenging due to the difficulty of predicting N availability as affected by the interaction of agronomic practices, soil properties, and weather. The end-of-season stalk nitrate test, which measures nitrate-N concentration in the lower sections of corn plants around physiological maturity, can be used to estimate corn N status and also determine soil, weather, and agronomic factors that influence N availability. We collected producer feedback and stalk nitrate surveys from a total of 2,737 fields throughout Indiana, USA, from 2011 – 2016. We also constructed a composite soil variable describing pertinent soil properties likely to influence N availability. We used continuation-ratio logit models to determine which agronomic factors commonly used by Indiana farmers and soil properties have significant influence on corn stalk nitrate status. Spring cumulative rainfall and seasonal precipitation were explanatory variables in separate models. Significant explanatory variables included previous crop and cover crop planted, N form and application timing, tillage type, total N applied, and precipitation. Furthermore, our soil property variable also had a significant influence on stalk nitrate status. Analysis of this large dataset enabled us to identify agronomic practices most likely to result in stalk nitrate values indicative of excess N, where perhaps reduced rate of application might be of benefit. This study demonstrated the value of collecting multiple year data for assessing the impact of a wide array of soil and environmental impacts and agronomic practices on N availability across a given farming region.