Scientific Irrigation Scheduling for Salinity Control of Irrigation Return Flow

Basic principles of irrigation water man- agement and irrigation scheduling are pre- sented. Commercial and agency groups ex- panded 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 frac- tion/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 coef- ficient. The effects of nonuniform water applica- tion 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 measur- ing water will be presented. Substantial im- provements can be made in irrigation efficien- cies before minimum .leaching fractions are reached on most western irrigated projects.