Water-Use Production Functions of Selected Agronomic Crops in Northwestern New Mexico, Phase II

The water requirement for growth of spring barley, pinto beans, and alfalfa was investigated in northwestern New Mexico. Results strongly suggest that the level of nitrogen fertility does not alter the water-use efficiency (WUE) of spring barley when WUE is expressed as a function of transpiration. WUE may change, depending on irrigation scheduling, if WUE is expressed as a function of evapotranspiration. We attribute this difference to differential soil-water evaporation. Further evidence supports the hypothesis that a common function exists independent of season, with respect to a given crop, relating economic yield to transpiration. Crop coefficients based on various methods of calculating potential evapotranspiration were found to vary considerably, as much as 50 percent, between years due in part to the difference in the evaporation component of the measured evapotranspiration. Consequently, caution should be exercised in using crop coefficients to predict alfalfa, pinto beans, and spring barley seasonal or intra-seasonal water requirements when the crops are grown under conditions requiring frequent light irrigation.