Understanding variable evapotranspiration (ET) throughout a field can help maximize yield on a per-acre basis, as well as assist with proper irrigation scheduling. The results from this study indicate that irrigation system distribution uniformity (DU) has a significant effect on the uniformity of ET during water-stressed periods. The study site involved intensely managed forage (alfalfa and winter grain hay) irrigated by center pivots being supplied with reclaimed water near Palmdale, California. During spring and early summer 2007 the center pivots were operating under deficit irrigation. In 2010, after the installation of reservoirs, water was applied to meet full evapotranspiration (ETc) demands. Using remote sensing of actual evapotranspiration, the variability in ETcfor the same pivots with the same crop was quantified. During the non-water-stressed period, ET uniformity was significantly better than during the water-stressed period (2007). The difference in uniformity was found to be attributable to irrigation system distribution uniformity. For the 540 ha used in this study, irrigation system DU was found to explain 55% of the ET nonuniformity during deficit irrigation. A method to predict the nonuniformity in ET as a result of irrigation system DU and water-stress level is presented.


Bioresource and Agricultural Engineering



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