Assessing whole-field sprinkler irrigation application uniformity

In order to assess whole-field sprinkler irrigation uniformity, an experiment was conducted to obtain water distribution profiles at 23 different pressures for each of five different sprinklers: Nelson R33, Nelson R33LP, Nelson R33 with road guard, Nelson R33LP with road guard, and Rainbird Mini Paw/LG-3. A mathematical model was developed to account for pressure variation throughout a fixed sprinkler system on a 10-ha field and to evaluate sprinkler irrigation uniformity for the whole field using interpolated water distribution profiles from the experimental data. The relationships between irrigation application uniformity and sprinkler pressure, sprinkler spacing, pressure variation, sprinkler type, and field topography were studied using the model. The results show that the coefficient of uniformity, CU, decreases rapidly when the pressure is below the low end of the manufacturer-recommended range; however, CU changes very little with pressure within the manufacturer-recommended range. The system application uniformity, CU_sys, is usually less when pressure variations at different locations in a field are considered, and a simple previously published equation to predict CU_sys is shown to closely approximate the CU from a more stringent calculation method. It was found that the impact of pressure variation (within the tested ranges) on application uniformity is less than that of the sprinkler spacing. Also, the effect of field topography on sprinkler application uniformity is relatively small for the cases tested herein.