Book Description

Efficient use of irrigation is essential to meet food production needs of growing global populations while ensuring long-term sustainability of freshwater resources. However, lack of on-farm irrigation data constrains understanding of irrigation variation and no framework exists to benchmark irrigation use using actual irrigation data. The following work investigates variation in irrigation using a database of ca. 1400 maize and soybean fields over 9 years in Nebraska and presents a framework to benchmark irrigation use using a separate database of ca. 1000 maize and soybean fields in Nebraska as proof of concept. "State-of-the-art" crop models estimated yield potential and irrigation water requirements for each field-year observation and were compared against producer-reported yield and irrigation. Precipitation and ETo accounted for >68% of observed year-to-year variation in irrigation in maize and soybean fields. Irrigation differed by ca.150 mm between regions due to differences in available water holding capacity. Weather and soils explained field-to-field variation in irrigation; however, the majority of field-to-field variation remained unexplained, attributable to producer behavior. Fields with above/below-average irrigation remained consistent across all years, suggesting behavioral components of irrigation variability. Findings illustrate the difficulty of predicting field-scale irrigation due to multiple biophysical and behavioral factors driving irrigation decisions. Increased availability of high-quality, on-farm irrigation data is needed to inform decision-making related to water resources and irrigated agriculture. Benchmarking found that 82% of fields reached ≥70% of yield potential. Nearly 75% of maize and ca. 40% of soybean fields were irrigated above simulated irrigation requirements, indicating room for improvement in irrigation use. Irrigation surplus increased with decreasing soil water holding capacity. Fields irrigated using high-level technology (e.g. soil water sensors) received 95 mm less irrigation than fields where irrigation decisions were not properly informed, with no yield difference between scheduling methods. Half of current irrigation volumes could be potentially reduced in above- or near-average rainfall years if current irrigation surplus is eliminated, but only 10% in drought years. The framework developed can be used to benchmark irrigation use for crop production at different spatial levels (field, region, state), help prioritize extension and research activities, and inform policy and incentive programs..