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Standardized Testing of Soil Moisture Sensors used in “Smart Controller” Irrigation Systems.

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Computers in Agriculture and Natural Resources, 4th World Congress Conference, Proceedings of the 24-26 July 2006 (Orlando, Florida USA) Publication Date 24 July 2006  701P0606.(doi:10.13031/2013.21855)
Authors:   Diganta D. Adhikari, Dave Goorahoo, David Zoldoske and Ed Norum
Keywords:   Smart Water Application Technology (SWAT); Soil Moisture Sensors, Standardized testing protocol; Time domain transmissivity (TDT); Amplitude domain reflectometry (ADR).

The development of Smart Water Application Technologies or SWAT was initiated by water purveyors who wanted to improve residential irrigation water scheduling. It is estimated that typical residential landscapes apply 30 to 40% more water than is required by the plants. Hopefully, the widespread adoption of smart controllers and soil moisture sensors would conserve a significant portion of the excess water applied. Over the past two years, the Center for Irrigation Technology (CIT) has been working closely with water purveyors statewide and the Irrigation Association (IA) as part of SWAT to develop standardized testing protocols for evaluating the reliability, accuracy and repeatability of commercially available soil moisture sensors. These sensors can provide closed-loop feedback to time-based system controllers, thereby allowing the controllers to recognize soil moisture levels and terminate irrigation events when soil moisture reaches predetermined levels. We discuss the testing protocol adopted by the IA for evaluating the sensors under laboratory conditions of varying levels of moisture, soil type, and salinity. We will also evaluate the data obtained from two different sensors operating on the principles of time domain transmissivity (TDT) and amplitude domain reflectometry (ADR), respectively. Preliminary findings indicate that for the tests conducted at -5, 20 , 25 and 30 C temperatures with the application of increasing salt solutions of 0, 1.5 and 3.0 dS/m on a sandy loam soil and coarse textured soil ( refer to Table 2), there was excellent correlation (r2 ranging from 0.89 to 0.99) between the volumetric water contents measured with the sensors and the calculated values. Calibration requirements, repeatability, and accuracy over the range of test conditions will also be discussed. We conclude the presentation with an outline of phase 2 of the testing protocol, which will focus on conducting similar tests outdoor on turf plots.

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