Scientific Irrigation Scheduling for Salinity Control of Irrigation Return Flow

Basic principles of irrigation water management and irrigation scheduling are presented. Commercial and agency groups expanded rapidly in the 1970's providing field-by-field scheduling services to over 600,000 acres in 1976. The leaching fraction used on projects can effect return flow quality. Most leaching fraction/return flow models hypothetically assume uniform water applications of exact quantities to attain targeted leaching fractions. The average or effective leaching fraction for a field is dependent on the irrigation uniformity coefficient. The effects of nonuniform water application on average leaching fractions will be presented, along with the probable effects of expected improvements in irrigation efficiency on return flow. Also, estimates of the accuracies in estimating evapotranspiration and measuring water will be presented. Substantial improvements can be made in irrigation efficiencies before minimum leaching fractions are reached on most western irrigated projects