UC Davis

Irrigation adoption is increasing in humid regions to offset short-term dry periods, especially at the peak of the growing season. Low soil moisture at the peak growth stage impacts yield and limits the plant's capacity to uptake nitrogen, resulting in low nutrient use efficiency (NUE). However, heavy rainfall on fields with supplemental irrigation may result in waterlogging and surface runoff, leading to nutrient leaching and runoff. This ultimately can lead to lower NUE, poor water use efficiency (WUE), reduced yields, and water quality impacts. This makes irrigation management challenging in humid regions, as irrigators must avoid both limited and excess water conditions. This field study aimed to develop and test an irrigation management methodology using real-time soil water availability, crop physiological status, water needs, and short-term weather forecasts information from National Weather Service. A rule-based approach determined by soil moisture depletion and short-term weather forecasts was used to trigger irrigation to avoid both stress and excess water conditions. This method was tested in two years of field trials in Suffolk, Virginia to quantify its impacts on yield, NUE, WUE, and financial returns in corn and cotton under four nitrogen application treatments. The relative impact of irrigation and nitrogen treatment was quantified using mixed effects models. The yield, NUE and WUE were impacted by both precipitation and irrigation patterns. Significantly different yields were observed under Nrates treatments for both corn and cotton. The trends of economic returns were similar to yield and were significantly different between recent and historic prices. This study also discusses the impacts of reliability and practical challenges of using Weather Informed irrigation in a field study.