MODELING DEFICIT IRRIGATION IN ALFALFA PRODUCTION

A conceptual agronomic model EPIC was extended to consider the effects of salinity in alfalfa production under optimal and water stress irri gation conditions. The extended model was calibrated and validated wit h observed lysimeter data. The model parameters that affected alfalfa yield and soil salinity the most were wilting point, field capacity, h ydraulic conductivity, nitrate concentration, biomass energy ratio, se eding rate, average soil salinity EC(e) at which crop yield is reduced by 50% (EC(50)), and initial soil gypsum concentration. The calibrate d and validated model was then applied to an alfalfa deficit irrigatio n study. The four irrigation treatments included optimum check, minimu m stress, short stress, and long stress, each of which produced differ ential alfalfa yields. The purpose of summer deficit irrigation was to ascertain how much agricultural water at what cost could be made avai lable for urban water uses during water shortfalls. The results of mod el simulation were found to be satisfactory under all irrigation treat ments though the model slightly overestimated the yields and underesti mated the soil EC(e) at the end of short and long stress treatments. A n economic component is included to determine the appropriate compensa tion for farmers undergoing a range of deficit irrigations.