BENCHMARKING ON-FARM MAIZE NITROGEN BALANCE IN THE WESTERN U.S. CORN BELT

A nitrogen (N) balance, calculated as the difference between N inputs and grain-N removal, provides an estimate of the potential N losses. We used N balance with other N-related metrics (partial factor productivity for N inputs, and yield-scaled N balance), to benchmark maize yields in relation with N input use in the US Corn Belt. We first used experimental data on grain-N concentration (GNC) to assess variation in this parameter due to biophysical and management factors. Subsequently, we used N balance and N-related metrics to benchmark yields in relation with N inputs in irrigated and rainfed fields in Nebraska using a large database (9,280 field-years). Similarly, we used this database to determine data requirements for robust N balance estimation for a given climate-soil domain and investigated the persistence of N balance. Finally, we used a database (311 field-years) with detailed management practices to identify drivers of N balance variation among fields. Analysis of experimental data indicated average GNC of 1.15%. Analysis of large database showed that irrigated exhibited smaller yield-scaled N balance than rainfed fields. There were fields that achieved high yields with small positive N balance, indicating that productivity and environmental goals can be achieved simultaneously. Important number of fields exhibited persistent large N balance over years which was associated with higher N inputs than other fields. There is substantial room to improve yield and/or reduce N balance through agronomic management like N fertilizer reduction and rotation with soybean. Important drivers of variation in N balance were water regime, sowing date, soil organic matter, timing and split of N fertilizer application. Producers risk perception plays an important role at explaining N balance variation across fields. A robust N balance can be estimated with at least four (irrigated) and six (rainfed) years and 100 fields per year per climate-soil domain, which, together with an existing spatial framework, can serve as basis to develop strategy to collect field-level data to monitor N balance for the entire US Corn Belt region, which, in turn, can help prioritize policy and research investments to ensure productivity with small N losses from agricultural production. Advisor: Patricio Grassin