Nitrogen economy in corn-soybean farming systems

Doctor of PhilosophyDepartment of AgronomyIgnacio A. CiampittiNitrogen (N) is the most limiting nutrient for producing maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] crops. The complex system governing the soil-plant N dynamics requires exploring multiple perspectives. Concomitantly, there is a marked need to deploy data-driven models that account for uncertainty in the processes of interest to provide improved N recommendations in both crops. Therefore, the objectives of this dissertation were: (i) to assess the contribution of environmental and crop management factors on the prediction of inherent maize productivity without N fertilizer; (ii) to identify the main drivers of both, expected values and uncertainties, of key components describing the process models for the maize yield response to N fertilizer; (iii) to summarize the impact of N and water management practices in maize grain quality; (iv) to study the residual effects of N management in maize on the following soybean crop; and, (v) to evaluate statistical techniques for the assessment of agreement between predictions and observations. In a joint effort between different academic and industry institutions in the US and Canada, a database with more than 1,200 maize N fertilization experiments (1999-2019) was built. Crop management factors such as previous crop and irrigation in combination with soil organic matter contributed to explain half of the variability of maize yield without N fertilization, while including spring weather variables (March-May) resulted in a similar performance than a framework including weather during the entire season. Crop management factors largely affected the prediction of the expected yield without N fertilizer, but just slightly impacted (