Reduced-runoff irrigation of alfalfa in Imperial Valley, California

This paper assesses the potential of the "reduced-runoff" surface irrigation method for clay soils to limit tailwater runoff and evaluate its impacts on crop production and soil salinity throughout a 3-year alfalfa hay production cycle in the Imperial Valley. Despite moderately saline field conditions, tailwater runoff was reduced to <2%, thereby reducing the annual water application by approximately 28% with no loss in hay yield or quality in comparison to countywide averages. The valley average applied-water yield efficiency (yield/applied water) was increased from 8.9 to 15.2 kg/ha-mm. When corrected for yield reduction due to salinity conditions (i.e., similar to 21 kg/ha-mm), this latter value is comparable to reported maximum alfalfa water-use efficiency (similar to 20 kg/ha-mm). Soil salinity accumulated (from 6 to 14 dS/m) at the 0.9-1.5 m depth interval of the soil profile, particularly in the lower 15% of the border checks by the end of the study. However, disking, a single leaching irrigation, and sweet corn production after termination of the alfalfa were adequate to reclaim the soil.