EVALUATING UNIFORMITY OF CENTER PIVOT IRRIGATION SYSTEMS IN WESTERN OKLAHOMA

Nonuniform application of water through center pivots can lead to under- or over-irrigation at parts of the field, which can lead to water stress and yield reductions or loss of limited water resources and leaching of applied chemicals, respectively. In this study, irrigation uniformity tests were performed to determine the application uniformity and conveyance efficiency of 24 center pivots in western Oklahoma. The average coefficient of uniformity and low quarter distribution uniformity of the tested systems were 78% and 69%, respectively. These values indicate an overall borderline acceptable application uniformity. The average water conveyance efficiency was 93%, indicating that 7% of pumped water was lost before reaching the soil surface. Measured ratios of collected water in each collector to the average collected water for corresponding center pivots were used to simulate the effects of observed nonuniformity on water fluxes for a 10-year period. Under-irrigation (e.g., caused by clogged nozzles) led to considerable reduction in crop transpiration at the simulation location in the Panhandle, while the decreasing effects were more notable for deep percolation for the location in west-central Oklahoma. Over-irrigation (e.g., caused by leaks or missing nozzles) resulted in substantially larger deep percolations at both locations.