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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED WATER RESOURCES MANAGEMENT FOR IRRIGATED AGRICULTURE IN THE PACIFIC NORTHWEST

Location: Northwest Irrigation and Soils Research

Title: Spatially distributed control netowork for flow proportional chemical injection with center pivot irrigation

Authors
item KING, BRADLEY
item Wall, R -
item Taberna, J - WESTERN AG RESEARCH

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 2009
Publication Date: October 13, 2009
Citation: King, B.A., Wall, R.W., Taberna, J.P. 2009. Spatially Distributed Control Network for Flow Proportional Chemical Injection With Center Pivot Irrigation. Applied Engineering in Agriculture. 25(5):677-683.

Interpretive Summary: 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 irrigation because it is relatively easy and is usually the least expensive method of applying fertilizer and other appropriately labeled chemicals. However, the standard practice of chemical injection at a constant rate results in systematic chemical application errors ranging from 7 to 22% for center pivot systems equipped with an end gun sprinkler and/or swing-arm corner watering system. Chemical injection proportional to center pivot system flow rate is one approach to reduce systematic chemical application errors. Commercial flow proportional chemical injection systems are rarely used on irrigation systems due to their cost and reliability. Real-time monitoring of center pivot system operating status as an alternative to direct flow measurement for flow proportional chemical injection was evaluated on a commercial center pivot irrigation system. Real-time monitoring eliminated the systematic chemical application errors in chemical application from a center pivot equipped with an end gun sprinkler and swing-arm corner watering system. Real-time monitoring of center pivot system operating status also provides for the record keeping and display of information that is useful to the producer for verifying correct irrigation system operation and trouble shooting irrigation system operation. Real-time monitoring of center pivot system operating status as an alternative to direct flow measurement for flow proportional chemical injection has the potential to be cheaper and more reliable than direct flow measurement.

Technical Abstract: 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 irrigation because it is relatively easy and is usually the least expensive method of applying fertilizer and other appropriately labeled chemicals. However, the standard practice of chemical injection at a constant rate results in systematic chemical application errors ranging from 7 to 22% for center pivot systems equipped with an end gun and/or swing-arm corner watering system. Chemical injection proportional to center pivot 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 irrigation system operating status to control the chemical injection rate so that it is proportional to system flow, thus minimizing systematic chemical application errors. A distributed control network was developed to facilitate real-time monitoring of end gun and corner swing-arm operating status using distributed sensing. The control network consisted of three network nodes that used the 480 VAC 3-phase power cable on the center pivot irrigation system as the communication medium. The control network was installed on a commercial 460 m (1510 ft) long center pivot system equipped with a corner-arm and end gun. Performance of the proportional chemical injection system based on real-time center pivot operating status was evaluated by injecting Rhodamine WT dye into the center pivot system and measuring its concentration in the applied water. The flow proportional chemical injection system eliminated the systematic errors in chemical application due to changes in center pivot system flow rate. Use of distributed sensing rather direct flow measurement for estimating center pivot system flow rate eliminates the need for straight sections of piping at the chemical injection site. Display and/or data logging of real-time center pivot operating status is an added benefit of using distributed sensing. This information is valuable to the producer for verifying correct system operation and trouble shooting system operation.

Last Modified: 8/27/2014
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