Relationship of in-season soil nitrogen concentration with corn yield and potential nitrogen losses

New process-based tools for predicting in-season soil nitrogen (N) levels has the potential to provide timely information for N management decisions for corn (Zea mays L.) production systems in the U.S. There is, however, little published data supporting the assumption that soil mineral N (SMN, NH₄-N + NO₃-N at 0–60 cm) is correlated with yield response at different vegetative growth stages. Moreover, the degree to which changes in SMN influence the risk of N losses is uncertain. Data from 32 site-years of field experiments in Illinois (2015–2018)—that included 12 combinations of N fertilizer rate, timing, and source—were used to evaluate the relationship between SMN concentration and grain yields across vegetative growth stages and estimate the exceedance probability of N losses. Overall, SMN across vegetative growth explained 46–61% of the variation in grain yield. Critical level of SMN that optimized yield decreased from 23.4 mg kg⁻¹ at V5-V7 to 9.1 mg kg⁻¹ at VT-R1 growth stage, but it was consistent, ranging from 14.7 to 16.3 mg kg⁻¹, among sampling periods between V8 and V16 stages. While increasing SMN from deficiency (below critical levels) to sufficiency (at critical levels) increased yields by 22% (11.8 vs. 14.4 Mg ha⁻¹), it also increased the probability of environmental N losses throughout vegetative growth, indicating a clear tradeoff between production and sustainability goals. These results help guide the development of sustainable in-season N management strategies by illustrating the importance of incorporating risks of environmental N losses when trying to reach optimum grain yield levels.