Long-term croplands water productivity in response to management and climate in the Western US Corn Belt

Global population growth and water scarcity are raising concerns about agricultural systems' ability to meet future food, fuel, feed, and fiber demands. Water productivity (WP), the ratio of crop production to water use, is crucial for assessing agricultural resilience and sustainability. Yet, research on WP often lacks long-term observational data to understand the impact of management and climate variability. Long-term monitoring of crop yield and water use, using Eddy Covariance technique, allows for accurate assessment of crop performance and their response to climate change in major cropping systems. In this study, we used data collected over a 20year period (2001-2020) to investigate the interannual variability in yield (Y), crop evapotranspiration (ET), and water productivity (WP, ratio of Y and ET), and their response to management and climate in three major cropping systems located in Eastern Nebraska: irrigated continuous maize, irrigated maize-soybean rotation, and rainfed maize-soybean rotation. Our results showed significant differences (p < 0.05) in WP between irrigated and rainfed sites, mainly attributed to variations in Y rather than ET, while there was no significant effect of crop rotation on measured responses. WP was 18.4% higher in irrigated maize in rotation relative to the rainfed site. Water input (mm, sum of precipitation and irrigation) was the main management factor in rainfed maize WP (R=0.67, p = 0.05) and Y (R=0.79, p < 0.05). Vapor pressure deficit was negatively correlated with Y in rainfed maize (R=-0.72, p < 0.05) and therefore was considered a determinant in WP (R=-0.7, p < 0.05). For soybean, soil water content had the highest correlations with Y and WP (irrigated: R=-0.77; rainfed: R=0.49, only significant in irrigated sites). These findings can aid in formulating strategies to enhance water productivity and resilience in the US Corn Belt.