Minimizing salt in drain water by irrigation management — Leaching studies with alfalfa

Abstract

An alfalfa experiment was conducted in the Wellton-Mohawk Irrigation and Drainage District of Southwest Arizona to determine the potential for minimizing the salt load in irrigation return flow by decreased leaching. Three leaching treatments of 5, 10, and 20%, replicated five times, were imposed on a 2-ha field. The crop was irrigated with Colorado River water (electrical conductivity of 1.3 dS m −1) through a lateral-move, spray-type irrigation system. Results were compared with those of an adjacent area irrigated with level basin flooding. The average annual evapotranspiration during the 4-year study was 1930 mm. Several indirect measures of the leaching fractions attained gave average values of 6.4, 9.3, and 13.1% for the three leaching treatments. Mean annual yields were 21.5 and 22.9 Mg ha −1 for 1977 and 1978 in the experimental plots, with no significant differences among leaching treatments, and 25.7 and 20.8 Mg ha −1 in the adjacent flooded check. The results suggest that full yields could be attained with as little as 5% leaching. Estimates based on average on-farm irrigation efficiency for alfalfa in the District in 1979, indicate that 5% leaching, if attainable, would reduce the salt load in the irrigation return flow by 39 000 Mg year −1 on 8 000 ha of alfalfa.