Factors Affecting Nitrogen Availability and Variability in Cornfields

Abstract

Core Ideas N application rate for corn should be estimated conditional to other influential factors to N availability. Guided sampling by aerial imagery for end‐of‐season stalk nitrate‐N test is a useful tool to benchmark N variability. N availability for corn is significantly affected by crop rotation, tillage, soil, and N form, rate, and timing. Nitrogen management in corn (Zea mays L.) is complicated by uncertainties in the agro‐ecological system. Consequently, current N recommendation systems provide accurate estimates of average N rates to apply across geographic regions but not to individual fields. To improve N use efficiency (NUE) and reduce negative environmental impacts, field‐specific N rates should be estimated using site factors that can have significant effects on N loss and availability. We surveyed 920 cornfields across the US Corn Belt and collected 3680 cornstalk samples during a 7‐yr period, 2008 to 2014. Aerial images of the corn canopies taken in late August were used to randomly select three sampling areas within three predominant soil types in each field. Cornstalk samples were evaluated for N status using the end‐of‐season cornstalk nitrate test (CSNT). We also collected data about site‐specific environmental conditions and management practices that had the potential to influence N loss and availability. Ordinal logistic regression (OLR) analysis was used to identify factors that significantly affected cornstalk N‐sufficiency levels, based on the CSNT. Results suggest that N rate alone is not a driving factor that influences N availability to a corn plant during the growing season. Rather, N rate recommendations should be estimated considering other site factors, including rainfall, previous crop, tillage practice, soil drainage class, and N form and timing. Our research findings are useful to support a field‐based adaptive management program and the 4Rs of Nutrient Stewardship management.