Influence of sprinkler height on irrigation performance of center pivot irrigator

Abstract: In most nozzle configuration software, the irrigation uniformity of center pivot irrigation system is simulated from the water distribution characteristics of single sprinkler at a special height. Influenced by the plant height and topographic slope, the actual installation height of sprinkler is often not equal to the simulated height and is kept constant during the growing season of crop as lack of the regulation apparatus, which resulted in the unknown irrigation uniformity and irrigation depth. To guarantee the irrigation uniformity and irrigation efficiency of center pivot irrigation system, the principle of keeping the sprinklers on the top of the plant height was proposed and a control apparatus was invented by changing the insert length of counterweight steel tube into the sag pipe to adjust the sprinkler height timely. In this study, the performance of the center pivot sprinkler system outfitted with D3000 non rotating nozzles spaced at 2.92 m was tested to verify the stability of irrigation uniformity and irrigation water depth at 5 installation heights of sprinkler (0.5, 1.0, 1.5, 2.0, and 2.6 m) and 3 outflow rates of sprinkler machine (8.8, 16.7, and 24.2 m3/h). The height of 1.5 m is the standard value simulated by nozzle configuration software. The outflow rates were obtained by using different sprinkler configuration. Catch cans were arranged in transect to obtain the irrigation water depth along the pivot lateral. The modified Heermann-Hein uniformity coefficient was calculated to evaluate the irrigation uniformity. During each test, the wind speed was smaller than 2 m/s. The results indicated that when the sprinkler was adjusted to the standard height of 1.5 m, the application performance of center pivot irrigation system was basically stable under the 3 outflow rates of sprinkler machine. The irrigation depth changed with zigzag wave along radial direction, and a target irrigation water depth could be obtained accurately through setting a specific rotation speed of the pivot. The modified Heermann-Hein uniformity coefficient along the pivot lateral ranged from 82.5% to 84.0%. When the sprinkler height was smaller than 1.5 m, the irrigation depth changed greatly along radial direction, especially at 0.5 m height, under which the modified Heermann-Hein uniformity coefficient significantly decreased by 23.9%. When the sprinkler height was greater than 1.5 m, the distribution of water irrigated along radial direction was more uniform, and there was no significant difference in uniformity coefficients among the 1.5, 2.0, and 2.6 m installation heights. After the sprinkler height was adjusted, although the irrigation water depth was obviously decreased at the height of 2.6 m because of the greater evaporation resulting from longer flying time, the mean absolute value of relative error for measured water depth was less than 10% compared with that at standard sprinkler height. The experimental results demonstrate that the sprinkler height can be raised timely when the plant height is bigger than 1.5 m to guarantee the uniformity coefficient and irrigation water depth of center pivot irrigation system.