Minimizing salt in drain water by irrigation management — Arizona field studies with citrus

Abstract

A field experiment was conducted for 5 years in the Wellton-Mohawk Irrigation and Drainage District of southwest Arizona to investigate the potential for reducing the salt load in irrigation return flow by decreased leaching in citrus. Leaching treatments of 5, 10, and 20%, replicated nine times, were established on mature Valencia orange trees ( Citrus sinensis L.) and compared with conventional flood irrigation management. The annual evapotranspiration was found to be about 1470 mm. The leaching fractions, determined indirectly by several techniques, were close to those intended. The leaching fraction for the flood check was 0.47. During the first 4 years, the leaching treatments had no observable influence on fruit yield or quality or on tree growth. During the last year of the study, however, the yield of the 5% leaching treatment was significantly lower than the other treatments. Thus, with some uncertainty, the leaching requirement for Valencia orange irrigated with Colorado River water exceeds 5% but is less than 20%. Results verify that water applications could be reduced substantially below typical commercial practice without loss of crop yield. At the conclusion of the experiment reducing the leaching fraction to 0.20 for the 3000 ha of citrus in the District would reduce the salt load in the irrigation return flow by 127000 Mg annually. After steady state conditions are reached at 20% leaching the annual reduction would be 42500 Mg.