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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING IRRIGATION MANAGEMENT FOR HUMID AND SUB-HUMID CLIMATES

Location: Cropping Systems and Water Quality Research

Title: Performance evaluation of a center pivot variable rate irrigation system

Authors
item Gossel, Arndt -
item Thompson, Allen -
item Sudduth, Kenneth
item Henggeler, Joseph -

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: June 12, 2013
Publication Date: July 21, 2013
Citation: Gossel, A., Thompson, A., Sudduth, K.A., Henggeler, J. 2013. Performance evaluation of a center pivot variable rate irrigation system. ASABE Annual International Meeting. Paper No. 131595956.

Interpretive Summary: Variable rate irrigation (VRI) technology allows changing the prescribed amount of water as an irrigation machine moves across a field. As with other variable rate applications, such as fertilizer, physical limitations of the machine mean that the actual application rate changes will differ from prescribed rate changes. Although such rate-change issues have been well-documented for variable rate fertilizer applicators, much less is known in the case of VRI. The purpose of this study was to evaluate the steady-state performance and dynamic response of a commercial VRI system installed on a center-pivot irrigation machine. The system did a good job of applying water uniformly, but there was considerable inaccuracy when transitioning from one VRI application zone to another. The results from this study will help irrigation engineers to optimize VRI prescriptions with respect to system operating characteristics.

Technical Abstract: Variable Rate Irrigation (VRI) for center pivots offers potential to match specific application rates to non-uniform soil conditions along the length of the lateral. The benefit of such systems is influenced by the areal extent of these variations and the smallest scale to which the irrigation system can respond. In this study, the VRI control system of a Valley 6000 center pivot was tested for uniformity and desired application. The purpose was to validate the ability of the concept rather than to conduct an exhaustive set of comparisons. Application collectors were spaced at uniform intervals of approximately 3 m along five to seven radial lines. The pivot was equipped to vary water depth in up to six separate application zones along the lateral. Uniformity tests were conducted in accordance with ASABE Standard S436.1. Wind speed was measured during all tests. Sprinklers were Nelson 3000 Spinners with wetted diameters of approximately 9 m. Suspended drop tubes positioned sprinklers approximately 2.5 m above the ground. Solenoid rates were varied from 40 to 100 percent in 20 percent increments. Results indicate that the system was capable of uniform application, though it was calculated with lower uniformity for the VRI tests than that of non-VRI tests. There was a gradual change of application depth along the lateral rather than an abrupt change between adjacent zones, reducing the uniquely managed areas. As expected, uniformity of application near towers was diminished.

Last Modified: 9/23/2014