ARS | Publication request: Using soil water sensors to improve irrigation management

Submitted to: Proceedings of the Central Plains Irrigation Conference
Publication Type: Proceedings
Publication Acceptance Date: February 3, 2012
Publication Date: February 21, 2012
Citation: Chavez, J., Evett, S.R. 2012. Using soil water sensors to improve irrigation management. Proceedings of the Central Plains Irrigation Conference, February 21-22, 2012, Colby, Kansas p. 197-202.

Interpretive Summary: Farmers using irrigation are faced with water availability restrictions, either natural or regulatory, and with droughty conditions. Thus, farmers must become more efficient in the use of water and produce more crop per drop. An accurate and easy to use soil water content sensor would be useful in deciding when and how much to irrigate, avoiding both over irrigation and under irrigation. Over irrigation wastes water and causes plant nutrients to be lost from the field. Under irrigation causes plant yield losses and decreases the yield obtained for the quantity of water applied. Scientists at the USDA-ARS Conservation & Production Research Laboratory, Bushland, Texas, and Colorado State University, Fort Collins, collaborated to field test several new soil water content sensors for their applicability to irrigation scheduling. They conducted tests in common irrigated soils of Texas and Colorado. They found two of the five sensors tested to be accurate enough for irrigation scheduling; and they provided advice as to their proper use and calibration in field soils.

Technical Abstract: Irrigation water management has to do with the appropriate application of water to soils, in terms of amounts, rates, and timing to satisfy crop water demands while protecting the soil and water resources from degradation. In this regard, sensors can be used to monitor the soil water status; and some can be used to calculate irrigation amounts and to decide when to optimally irrigate. This article consists of two parts: 1) presentation of different soil water sensor technologies, and 2) accuracy assessment of selected sensors. The selected sensors included the Acclima (ACC) time domain transmissometer (Acclima, Inc., Meridian, ID), the CS616 and CS655 water content reflectometers (Campbell Scientific, Inc., Logan, UT), the Hydra Probe (Stevens Water Monitoring Systems, Inc., Portland, OR), and the 5TE (Decagon Devices, Inc., Pullman, WA). Sensed soil water content values, in a sandy clay loam soil and a silty clay loam soil, were compared with corresponding values derived from gravimetric samples and TDR readings. Factory based calibrations performed well for the ACC and CS655, but not for the other sensors. The ACC and CS655 sensors were promising for irrigation management, although proper installation is important. Evaluations indicate that a linear calibration for the ACC and the CS616 sensors could improve the water content readings.