|NGUYEN, ANH - University Of Missouri|
|THOMPSON, ALLEN - University Of Missouri|
|Sudduth, Kenneth - Ken|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/20/2015
Publication Date: 11/10/2015
Citation: Nguyen, A., Thompson, A.L., Sudduth, K.A., Vories, E.D. 2015. Automating variable rate irrigation management prescriptions for center pivots from field data maps. Irrigation Symposium: Emerging Technologies for Sustainable Irrigation, November 10-12, 2015, Long Beach, California. doi: 10.13031/irrig.20152147794.
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, and that the physical characteristics of the irrigation machine (e.g., center pivot) need to be considered in developing an application plan. The purpose of this study was to automate creation of such application plans. This was done by developing a computer program to integrate pivot system geometry and VRI capability with field data maps in the creation of an application plan. The program was tested by using it to simulate application of different control strategies to a research center pivot. All strategies reduced water use compared to conventional, single-rate operation, with a maximum savings of 15% for the test field. The results from this study will help provide irrigation engineers with a new tool to optimize VRI prescriptions with respect to system operating characteristics.
Technical Abstract: Variable rate irrigation (VRI) enables center pivot systems to match irrigation application to non-uniform field needs. This technology has potential to improve application and water-use efficiency while reducing environmental impacts from excess runoff and poor water quality. Proper management of VRI systems depends on correctly matching the pivot application to specific field temporal and areal conditions. However, translating field maps to VRI prescriptions can be difficult and time consuming. The objective of this study was to automate development of VRI pivot control programs based on GIS maps of field conditions. Specifically, a computer program written in Visual BASIC, was developed to match pivot system geometry and VRI capability (i.e. resolution of machine control for azimuth and sprinkler cycling) with GIS grid-based field data. It requires the user to input specific pivot system information including sprinkler wetted diameter and spacing, system flow rate, lateral length, sprinkler zone locations, and design application depth when set at 100 percent rotation speed. Examples of field data maps useful to develop prescriptions were made based on variations in soil texture. The program can be used on VRI systems with individual sprinkler control, defined sprinkler zones, or system rotation speed changes. Results for a specific field indicated that all three methods of VRI management resulted in reduced potential runoff, and that individual sprinkler and zone control provided the best reduction. VRI with speed control was improved when the inner portion of the pivot was not included in developing prescription maps. Irrigating the field as a standard pivot with no VRI and maximum application depth for the soil with highest sand content resulted in over 15% of the applied water being lost to potential runoff.