Assessing the impacts of pre-growing-season weather conditions on soil nitrogen dynamics and corn productivity in the U.S. Midwest

Improving nitrogen (N) use efficiency is urgently needed to achieve co-sustainability of agricultural productivity and environmental quality. Environmental conditions and farming management practices affect the N cycle in agroecosystems. Particularly, weather conditions during the pre-growing-season (e.g. winter and early spring for the U.S. Corn Belt) can influence the dynamics of soil inorganic N (SIN) content and have implications for the end-of-season crop yield. Here, we used an advanced agroecosystem model, ecosys, to assess the consequences of different pre-growing-season weather scenarios in terms of both SIN dynamics and crop productivity. We first benchmarked ecosys using extensive N trial data collected across the U.S. Midwest, and found that ecosys captured the N fertilizer-yield responses and field-scale N cycle dynamics. We then used ecosys to conduct multiple experiments by changing the pre-growing-season precipitation and temperature, and assessed how these changes affected soil N dynamics and crop yield. We found that: (1) wetter pre-growing-seasons reduced SIN content through increasing leaching, leading to a reduction in corn grain yield of 0.54–0.86 Mg/ha (5–14%) under no fertilizer and of 0.21–0.33 Mg/ha (1–3%) under the normal N fertilizer rate (167 kg N/ha; Illinois average N fertilizer rate in 2018); yield loss induced by higher pre-growing-season precipitation can be eliminated by applying more N fertilizer in spring; and (2) colder pre-growing-seasons can reduce SIN content through decreased N mineralization and enhanced leaching. Both factors further contribute to corn yield loss of 0.10–0.68 Mg/ha (2–8%) under no fertilizer and of 0.12–0.48 Mg/ha (1–4%) under the normal fertilizer rate; however, in this case adding more fertilizer does not necessarily eliminate the yield loss caused by the colder pre-growing-season, because the lower temperature not only causes SIN deficiency but also reduces early-growing-season active root nutrients uptake and crop N demand by cooling soil temperature. These findings expand our understanding of the impact of weather conditions on crop yield and can inform improvements in N fertilizer use efficiency in the U.S. Midwest agroecosystems.