Assessing the impacts of pre-growing-season weather conditions on soil nitrogen dynamics and corn productivity in the US 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-growingseason, 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.

Automated summary

Improving nitrogen use efficiency is crucial for the co-sustainability of agricultural productivity and environmental quality. Weather conditions before the growing season can significantly impact soil nitrogen dynamics and crop yield. Through modeling experiments, we found that wetter and colder pre-growing seasons can reduce soil inorganic nitrogen content and lead to yield loss. These findings provide insights for enhancing nitrogen fertilizer use efficiency in the U.S. Midwest agroecosystems.