Dynamic Adjustment of Center Pivot Nozzle Height: An Evaluation of Center Pivot Water Application Pattern and the Coefficient of Uniformity

This study assesses the potential of dynamic nozzle height adjustment for overhead irrigation systems. This system would maintain the nozzle or emitter a constant distance above the crop canopy throughout the growing season and would dynamically respond to variability in canopy height across the field. Within such systems, nozzle height would no longer be fixed in space and time. Nozzle heights would instead vary across space and time. This dynamic system response may therefore have adverse impacts on water application uniformity. The impact of DESA on application uniformity was assessed in three steps. First, changes in individual sprinkler patterns for pressure, nozzle type, flow rate, and nozzle height were measured in controlled experiments. Next, parametrized equations of the individual sprinkler patterns and how they are altered by nozzle height are developed. Next, the Center Pivot Evaluation and Design software was used to simulate theoretical uniformity, and these simulations were tested against field measurements of the coefficient of uniformity. Finally, we use the parameterized equations within the Center Pivot Evaluation and Design software to simulate the coefficient of uniformity for pivots with constant nozzle heights with a random distribution of nozzle heights, which simulate a dynamic elevation system. It was found that the uniformity coefficient decreased by 4-6% as the distribution of heights throughout the pivot become more variable, due to localized dynamic height adjustment. Systems equipped with nozzles with triangular spray patterns were less impacted than systems equipped with nozzles with elliptical spray patterns.