Spatially Distributed Control Network for Flow Proportional Chemical Injection with Center Pivot Sprinkler Irrigation

The agricultural production practice of injecting a chemical into an operating irrigation system and applying it to the field area with the water is known as chemigation. Chemigation is a widely adopted practice with center pivot sprinkler irrigation. However, the practice of chemical injection at a constant rate with center pivot sprinkler irrigation systems equipped with an end gun and/or swing-arm corner watering system results in systematic chemical application errors ranging from 7% to 21% due to systematic changes in system flow rate. Chemical injection proportional to center pivot sprinkler system flow rate is one approach to reduce systematic chemical application errors. The objective of this project was to test the feasibility of using real-time monitoring of center pivot sprinkler irrigation system operating status to control chemical injection rate proportional to calculated system flow rate, thus minimizing systematic chemical application errors. A spatially distributed control network was developed to facilitate real-time monitoring of end gun and swing-arm corner watering system operating status and pressure. The spatially distributed control network consisted of three network nodes at specific locations along a center pivot sprinkler irrigation lateral that used the 480 VAC 3-phase power cable on the center pivot sprinkler irrigation system as the communication medium. The spatially distributed control network was installed on a commercial 460-m (1510-ft) long center pivot sprinkler system equipped with an end gun and swing-arm corner watering system. Performance of chemical injection proportional to calculated flow rate based on real-time center pivot sprinkler irrigation system operating status was evaluated by injecting Rhodamine WT dye into the center pivot sprinkler irrigation system water supply and measuring its concentration in the applied water. Mean dye concentration varied by 26% under constant rate chemical injection and 2% under flow proportional chemical injection due to systematic changes in center pivot sprinkler irrigation system flow rate. Use of the flow proportional chemical injection system reduced the coefficient of variability in measured dye concentration of applied water by 54% from 0.100 to 0.046. Use of the spatially distributed control network for calculating center pivot sprinkler system flow rate eliminates the need for straight sections of unobstructed piping at the chemical injection site. Display and/or data logging of real-time center pivot sprinkler operating status is an added benefit of using the spatially distributed control network. This information provides the ability to monitor, diagnose, and troubleshoot center pivot sprinkler system operation. Commercialization and adoption of the technology could reduce systematic chemical application errors and facilitate maintenance and operation of center pivot sprinkler irrigation systems equipped with an end gun and/or swing-arm corner watering system.

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