Submitted to: Proceedings of the Central Plains Irrigation Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/17/2015
Publication Date: 2/17/2015
Citation: Oshaughnessy, S.A., Evett, S.R. 2015. Zone edge effects with variable rate irrigation. Proceedings of the Central Plains Irrigation Conference.
Interpretive Summary: Water consumption by the agricultural sector in the Texas High Plains region is a significant water use and farmers must find ways to irrigate more efficiently. Data on the regularity at which a variable rate sprinkler system applies water over a field can improve irrigation management. A variable rate irrigation system can be used to customize irrigation amounts over a field to meet differing crop needs. However, there are peculiarities associated with the operation of this type of sprinkler system. In this study catch can tests were used to help to define the advantages and the limitations of such a system.
Technical Abstract: Variable rate irrigation (VRI) systems may offer solutions to enhance water use efficiency by addressing variability within a field. However, the design of VRI systems should be considered to maximize application uniformity within sprinkler zones, while minimizing edge effects between such zones along the lateral pipeline and in the direction of sprinkler movement. A number of factors influence edge effects, including equipment design, sprinkler-wetting pattern, wind speed and direction, and differences in watering application rates between adjacent sprinkler zones. This paper reviews the performance of a commercial three-span VRI center pivot system designed with drops spaced 5 feet apart, equipped with fixed spray plates and low drift nozzles at an elevation of 5 feet above the ground. Multiple catch can tests were conducted in a windy location to assess the application uniformity of the VRI system within sprinkler zones along the pivot lateral and in the direction of pivot movement, and to quantify edge effects within these zones. Watering application rates were varied at levels of 100%, 80%, 70%, 50% and 30% of 1.0 or 2.0 inches. The overall mean coefficient of uniformity and distribution lower quarter values within the sprinkler zones were 89.9% and 84.5%, respectively. The width of edge effects at the borders of the sprinkler zones varied between 5 and 20 ft., while the mean length of the edge effect in the direction of pivot travel was 30 ft. Edge effects were mainly imposed by the operation of the VRI system, but wind speed and direction intensified the edge effects.