WATER FLOW RATES FROM A SITE-SPECIFIC IRRIGATION SYSTEM

Abstract

Site-specific irrigation is defined as delivering different prescribed depths of water to specific areas in irrigatedfields. Since the 1990s, site-specific irrigation research has been expanded to include the delivery of water and nutrients tospecific field areas based on soil type, soil moisture status, crop needs, and other user-defined objectives. A site-specific centerpivot irrigation system was designed and installed in a field with highly variable soils of the U.S. eastern coastal plain. Thesystem consisted of 13 segments along the 140-m length of the three-tower center pivot with three delivery manifolds in eachsegment. The system was designed to apply approximately 12.5 mm of water in any selected segment when operated at 50%travel velocity. Quantifying water application depth and uniformity from the site-specific irrigation system is essential todocumenting the systems performance and interpreting experimental results. We developed a measurement system to evaluatethe water delivery rates of the irrigation system. We compared the measured water delivery from each segment of thesite-specific irrigation system to the design parameters. We found that the irrigation system was delivering water to the controlareas at rates approximately as it was designed. A total of 77 segment and manifold combinations were tested. Of these77 combinations, we found that 7 had flow rates greater than 10% different from the design flows. The manifolds with the lowerflow rates typically were more likely to differ significantly from their design values. This was most likely related to potentialclogging of the low flow nozzles that have smaller orifices. When the manifolds were used in combination, they compensatedfor each other and produced application depths near the design depths.