Application of chemicals with irrigation water is a widely adopted practice with center pivot irrigation systems, however, the standard practice of chemical injection at a constant rate results in systematic chemical application errors ranging from 7 to 22% for center pivots equipped with a corner watering attachment and/or an end gun. This project evaluates the feasibility of a less expensive and more reliable means to control flow proportional chemical injection with center pivot systems than currently commercially available to reduce systematic chemical application errors. OBJECTIVES: The overall objective of this project is to evaluate the feasibility of using real-time monitoring of center pivot irrigation system operating state to control chemical injection rate proportional to center pivot flow rate. The specific objectives are to: 1) develop an electronic based system for real-time monitoring of operating pressure and sprinkler status on center pivots equipped with a corner watering attachment and/or end gun, 2) use the real-time information to calculate the flow rate of the center pivot system and use this flow rate to control the flow rate of a chemical injection pump to maintain constant chemical concentration in the applied irrigation water, and 3) field-test operation of the real-time monitoring system on a commercial center pivot system to evaluate operational performance. Results of the field tests will be used to evaluate technical feasibility. APPROACH: A commercial center pivot system with a corner watering attachment and end gun will be used to evaluate feasibility of controlling chemical injection rate proportional to calculated system flow rate. The on/off status of sprinkler control valves on the corner watering attachment along with the on/off status of the end gun and operating pressure of the end gun will be used to calculate center pivot flow rate based on sprinkler package design specifications. The operating state of sprinkler control valves and end gun will be monitored in real-time using power line carrier based data communications. The calculated system flow rate will be used to control a variable rate chemical injection system to maintain constant chemical concentration in the applied irrigation water as the center pivot system flow rate continually changes in response to changes in operating status. The flow proportional chemical injection system will be used to apply in-season nitrogen fertilizer to potatoes with applied irrigation water. Samples of the applied irrigation water will be collected at ten-degree increments around the center pivot irrigated field and analyzed for nitrogen concentration. Nitrogen concentration in the applied irrigation water will be monitored four times during the season, twice with flow proportional chemical injection and twice with constant rate chemical injection. Ideally, nitrogen concentration in the applied irrigation water will be constant under flow proportional chemical injection. Significantly reduced (p<0.05) variability in nitrogen concentration in the applied irrigation water compared to that for constant rate chemical injection will demonstrate feasibility of controlling chemical injection rated based on real-time calculated center pivot system flow rate. PROGRESS: 2004/05 TO 2005/12 The purpose of this project was to determine the technical feasibility of using real-time monitoring of center pivot irrigation system operating status as a reliable means of controlling chemical injection rate proportional system flow in order to minimize systematic errors in chemical application due to end gun and/or corner water system operation. A distributed control network was developed that used the 480 VAC 3-phase power cable on the center pivot irrigation system as the communication medium. The distributed network consisted of three network nodes. The master network node was located at the pivot point and used to display current center pivot operating state, log operational data at 5-minute intervals, and control the flow rate of the chemical injection pump. One network slave node was located on the center pivot lateral at the corner watering system swing joint and used to collect swing-arm sprinkler valve operating state and GPS location. The second network slave node was located on the center pivot lateral at the drive wheel tower of the swing-arm and used to monitor pressure of the end gun. The distributed control network was tested on a 10-span, 1510-ft long center pivot irrigation system equipped with a corner watering system and end gun. Rhodamine WT dye was injected through the irrigation system to evaluate performance of the flow proportional chemical injection system. Water samples were collected at 5 degree angular increments around the field for dye concentration analysis. Results show that the proportional chemical injection system essentially eliminated the systematic chemical application errors caused by operation of the center pivot corner watering system and end gun. The distributed control network provides value beyond flow proportional chemical injection system. In our field tests, it became readily apparent that the producer has no way of verifying proper operation of the corner watering system. Currently, if water is flowing from the sprinklers, the corner watering system is assumed to be working. Real-time monitoring and display of sprinkler valve status and comparing that with visual observations of sprinkler operation provides an effective means of evaluating corner watering system operation and trouble shooting. The distributed control network also allows monitoring and display of end of system lateral pressure to verify adequate system pressure. Inclusion of GPS location with logged operational data provides a means to determine seasonal water application depth and water application depth per revolution of the center pivot based on known system flow rate and travel speed. The results of this project demonstrate that the distributed control network for real-time monitoring of center pivot operating status has great commercial potential as a means of improving water and chemical application of center pivot irrigation systems. IMPACT: 2004/05 TO 2005/12 Field testing clearly demonstrated that using real-time monitoring of center pivot irrigation system operating state to control chemical injection rate proportional to center pivot flow rate is technically feasible. Our results show that the flow proportional chemical injection system nearly eliminated the effect variations in center pivot system flow rate due to end gun and swing-arm operation have on chemical concentration in applied water. The results could be improved by using a center pivot flow rate model that accounts for system operating pressure fluctuations on center pivot flow rate. The distributed control network used for real-time center pivot system monitoring is easy to install and provides an economical means for distributed sensor communications as it uses the existing center pivot power cable for the communication medium
