Tejinder Singh
Water is one of the most important resources for agriculture in the western United States. In semi-arid regions, farmers depend on irrigation to grow crops, but water supplies are becoming less reliable because of drought, declining snowpack, groundwater depletion, and increasing competition for limited water. Improving agricultural water use is therefore not simply about applying less water. It also requires understanding where water goes after it enters a field, how long it remains available to crops, and how farmers can use that information to make better irrigation decisions. This dissertation follows water through irrigated agricultural systems to better understand how soil, crops, irrigation technologies, and management decisions shape water use. The research combined field experiments, laboratory soil measurements, field-installed sensors, water balance modeling, and producer surveys. Together, these methods were used to study how water moves through soils, how much water crops use, how irrigation affects soil conditions over time, and why some decision-support tools are easier for farmers to adopt than others. The results show that improving water use requires both better measurements and better management. Soil amendments such as gypsum and compost improved soil water movement under laboratory conditions, although field responses were more variable. Low-elevation sprinkler systems improved water productivity compared with conventional mid-elevation systems, but benefits depended on crop type, irrigation amount, genetics, and field management. Field-installed sensors captured realistic drying patterns and helped estimate drainage below the root zone, while also showing that shallow groundwater can sometimes supply water back to crops. Long-term irrigation with sprinklers increased soil bulk density and compaction compared with rainfed conditions, showing that sprinkler irrigation affects not only water delivery but also the soil environment where roots grow. Producer survey results showed that farmers recognize water scarcity and are interested in tools such as soil moisture sensors, weather stations, flow meters, and irrigation system evaluations. However, cost, technical knowledge, equipment maintenance, and difficulty interpreting data remain major barriers. Overall, this dissertation shows that agricultural water optimization is a system-level challenge. Conserving water while sustaining crop production requires connecting soil science, crop water use, irrigation technology, drainage, and producer-centered decision support.