Water Use Variability in Irrigated Level Basins

Abstract

ABSTRACT AN understanding of the expected variability of crop water use under field-size, surface irrigation conditions is needed to improve irrigation designs and water management scheduling procedures. A 1985 field study evaluated water use variability under three irrigation schedules and two border lengths. High water distribution uniformities of 85% or greater with a level-basin irrigation system resulted in higher irrigation application efficiencies averaging 95% for a dry irrigation treatment compared with 89 and 83%, respectively, for medium or wet treatments on a wheat crop. A shorter irrigation border length of 190 m compared with 251 m did not improve irrigation water distribution or application efficiencies. Water use (evapotranspiration) was affected by irrigation application amounts but not border length, and water application and evapotranspiration variability were significantly correlated. The coefficient of variation in water use was nearly doubled on the drier than the wetter irrigation treatment with as much as 13% variability occurring on the dry treatment. The higher coefficient of variation in water use on the dry was attributed to primarily soil and crop factors. Spatial interdependence was exhibited for seasonal irrigation water applications and water use at distances of less than 15 to 30 m (50 to 100 ft) suggesting that these minimum spacings were needed for soil water measurements. Greater attention needs to be placed on improved irrigation management for reduced irrigation water applications in order to minimize the effects of spatial variabilities attributed to the irrigation system, soil, and crop parameters.