This study aimed at conducting an impact evaluation of irrigation management practices in processing onion production. A three-year experiment was carried out in 15 commercial processing onion fields under different irrigation methods of furrow, solid-set sprinkler, and subsurface drip. The experimental sites were located in the Imperial Valley, California’s low desert region. All fields were on a 40-inch bed, six plant rows per bed with a spacing of 2.5-in between planting lines. The fields had a variable soil type with predominate soil texture from fine sandy to silty clay loam. Water, nitrogen, and energy used, bulb weights, soil moisture, soil nitrate and salinity, and actual evapotranspiration were measured in each site. A wide range of seasonal irrigation water applied was observed across the experimental sites. Irrigation water applied varied from 3.3 ac-ft/ac in a drip irrigated field to 6.9 ac-ft/ac in a furrow irrigated field. The results demonstrated that utilizing subsurface drip irrigation in processing onions could conserve 0.8 and 2.4 ac-ft/ac water in compared with solid-set sprinkler and furrow irrigation systems, respectively. The water productivity, the ratio of onion bulb weight to water applied, was determined 4.9, 4.3, and 2.7 t/ac-ft for the drip, sprinkler, and furrow irrigated fields, respectively. A greater nitrogen use efficiency was found in the drip irrigated fields compared to the sprinkler (15.2% points) and furrow (62.1% points) irrigated fields. The findings illustrated a higher salt accumulation on the topsoil (0-6 in. depth) in the drip irrigated fields. In other words, drip irrigation could cause salinity impacts in desert processing onions, and therefore, more frequent light irrigation events may be an effective tool to manage salinity. More nitrate leaching was also observed from the topsoil in the sites irrigated by sprinklers. Energy productivity, the ratio of onion bulb weight to fuel consumption, was 48.3% points higher in the drip fields than the sprinkler fields. The results revealed that irrigation practice has a significant impact on resource-use efficiency and environmental issues.
