Effects of Irrigation Nonuniformity on Nitrogen and Water Use Efficiencies in Shallow-rooted Vegetable Cropping Systems

Abstract

This research tests the hypothesis that decreasing lateral spacing from 45 to 35 feet in solid-set sprinkler systems increases the uniformity of irrigation water distribution and improves water and N fertilizer use efficiencies. Three different spacings between sprinkler laterals (35', 40', and 45') were set up in three blocks in a 60-acre commercial carrot field in Western Kern County in California's San Joaquin Valley. Determinations of irrigation water distribution uniformity, yields, crop water use, plant growth, and nitrate leaching were made. Mean sprinkler distribution uniformities (DU) were found to be 80.6%, 78.1%, and 86% for the 35-, 40-, and 45-ft spacings, respectively. Total carrot yield and quality did not differ significantly among the three spacings, corroborating the finding that irrigation uniformities were similar among the treatments. Although the three lateral spacings evaluated in this initial experiment did not result in major differences in irrigation uniformity, total yields, or quality, the findings of this initial stage of our research are significant. They point to the need for new assessments of currently used protocols for evaluating sprinkler irrigation management of water and nitrogen fertilizer if they can be confirmed by repeated trials in coming years.