Alfalfa Yields and Evapotranspiration Response to Static Water Tables and Irrigation

Abstract

ABSTRACT INDIVIDUAL harvest alfalfa yields and evapo-transpiration (ET) were evaluated for 2 years in a lysimeter experiment. Four constant water-table depths and three surface irrigation levels were the independent variables. Sources of water to meet ET demands were rainfall, irrigation, and the water table in addition to soil-stored water. The highest alfalfa yield for both years was 8.0 t/ha and occurred in the first harvest in 1979 with the 155 cm water table and 1.3 irrigation level (1.3 x calculated ETp). Rainfall, surface irrigation, and sub irrigation contributed 48.6, 24.7, and 26.7%, respectively, of the total actual ET. The shallowest (46 cm) water-table depth had highest ET and lowest yields compared to the other water-table depths (101, 155, and 210 cm). An economic analysis of total ET showed that the greatest monetary values of sub irrigation, within a given water-table depth, were with the low surface irrigation level while the lowest monetary values of subirrigation but highest costs of surface irrigation were at the high surface irrigation levels. The data showed that a range of water-table depths from 101 to 210 cm provided a high percentage of alfalfa ET by subirrigation which reduced surface irrigation requirements.