Submitted to: International Irrigation Show
Publication Type: Proceedings
Publication Acceptance Date: 11/6/2011
Publication Date: 11/6/2011
Citation: Oshaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2011. Application uniformity of a commercial center pivot variable rate irrigation system. International Irrigation Show, November 6-8, 2011, San Diego, California. 2011 CDROM.
Interpretive Summary: Variable rate irrigation (VRI) systems provide flexibility in applying irrigation water by allowing varying rates of water to be applied along the pivot lateral. This functionality allows a farmer to treat inconsistent issues within a field. Such issues include changes in elevation, soil texture, and disease or pest infestation. It is common to divide a field into management zones, with the goal that each management zone be as homogeneous as possible. Although variable rate irrigation implies non-uniformity on a field scale level, uniformity of application is very important within each management zone. We performed multiple catch can trials at Bushland, Texas to determine the application uniformity of a commercial VRI system for a 3-span center pivot. Catch cans were placed in radial and grid patterns to test the uniformity in multiple zones along the pivot lateral at different watering rates. We also placed catch cans in a circular pattern to test the circular uniformity. Results showed that the Heerman and Hein coefficient of uniformity was in the range of 88% to 91%. These values compared well to uniformity results reported for center pivot systems in the literature. Surprisingly, there were no significant differences in uniformity for the higher watering levels or among span locations. Some irrigation water was lost to evaporation and drift during the tests, which was expected due to the high wind speeds under which the tests were conducted. High winds are typical for the area.
Technical Abstract: With the advent of commercial variable rate irrigation (VRI) systems, there is a great interest in using them to improve water use efficiency, implement deficit irrigation strategies in water limited regions and manage water applications for many other important objectives. Multiple catch can trials were performed to determine the application uniformity of a commercial VRI system for a 3-span center pivot. Catch cans were used in radial transects and grid patterns to test the uniformity in multiple zones along the pivot lateral at different watering rates (100%, 80%, 70%, 50%, and 30% of nozzle "ON" time), and in an arc-wise pattern to test the circumferential uniformity and sector-wise resolution of the system. Results showed that the Herrmann and Hein coefficient of uniformity (CUHH) and the lower-quarter distribution uniformity (DUlq) were significantly lower when the watering rate was 30%; but there were no significant differences in uniformity for the increased watering levels or among span locations. With respect to circumferential uniformity, the mean CUHH and DUlq values were 88.1% and 0.82; these values were not significantly different from those obtained when catch cans were arranged in a transect pattern. The mean evaporation and drift loss for the transect-type trials was 10.8%.