摘要：Irrigated agriculture is generally considered to be more productive than rainfed agriculture at any given location. This difference in crop yield between irrigated and rainfed production ('Irrigation-limited yield gap' or ILYG) is subject to spatio-temporal variability, due to differences in management, environmental conditions, soils, and policy. However, quantification of ILYG and its associated variability remains uninvestigated. In this study, we analyzed the spatio-temporal dynamics of county level-ILYG for nine major irrigated crops in the United States: maize, soybean, spring wheat, winter wheat, alfalfa, sorghum, cotton, barley and oats from around 1950 to 2015. ILYG was found to be highly specific to crop and location and has been increasing, in general, over time, albeit with regional differences. Maize had the greatest ILYG magnitude on a national basis, with cotton ILYG showing highest temporal rates of increase. Increased ILYG variability over the study period was found for all crops, except cotton, which also showed the highest magnitude of long-term mean variability. Maps and key information in this article are significant to irrigation research, policy and decision-making, plant breeding, groundwater withdrawal allocation strategies and producers to identify pertinent regions using historical ILYG for optimizing farm irrigation management strategies to enhance overall national agricultural productivity.
