Yield of Alfalfa and Cotton as Influenced by Irrigation

Water resource planners need water-producton functions, the relationship between yield and evapotranspiration,to determine the economic impact of various water allocation decisions. They also need to know the transferability of the functions within and between states. Cotton (Gossypiurn hirsutum L.) and alfalfa (Medicago sativa L.) were irrigated at Las Cruces, New Mexico, with a range of water levels using a sprinkler-line source to determine yield and evapotranspiration under deficit irrigation. Also, alfalfa was grown at five locations and cotton was grown at two locations in New Mexico, including Las Cruces, in nonweighing lysimeters that were flood irrigated to measure the yield and evapotranspiration under nonlimiting soil-moisture conditions. A linear water-production function was observed for alfalfa. This function appeared to be transferable to any location in New Mexico, based on data from five locations within the state, and was statistically the same as alfalfa water-production functions for Nevada, Nebraska, and North Dakota. A linear water-production function was also observed for cotton, but this function was applicable only for the two areas in southern New Mexico where the study was conducted. The cotton water-production function for New Mexico was statistically different from the reported water-production function of the similar study conducted in California. The cotton water-production function had a lower coefficient of determination than the alfalfa water-production function since cotton was harvested for lint and seed rather than biomass. This study indicated that biomass production may require the same amount of evapotranspiration regardless of site and management differences, as in the case of alfalfa, but that lint or seed production per unit of water will vary from place to place.