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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 7/16/2013 Publication Date: 7/16/2013 Citation: Evett, S.R., Schwartz, R.C. 2013. An overview of soil water sensors for salinity & irrigation management. [abstract]. 2013 CDROM Interpretive Summary: 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. Accurate irrigation management is even more important in salt affected soils or when irrigating with brackish water. Various sensors can be used to monitor the soil water status; and some can be used to calculate irrigation amounts and to decide when to irrigate. This presentation consists of three parts: 1) a review and comparison of different electromagnetic (EM) soil water sensor technologies (capacitance or frequency domain and time domain) with attention to accuracy and usefulness for irrigation scheduling, 2) a discussion of the prevalence and seriousness of soil salinity in different irrigation systems and of the strong negative effects of salinity on accuracy of most sensors, and 3) accuracy assessment of selected sensors. The frequency domain (capacitance) soil water sensors were found to be too inaccurate and variable for use in irrigation scheduling. The time domain sensors were found to be accurate, though too expensive for routine use and difficult to install deeply, which motivated the research on a lower-cost deep profiling soil water content sensor based on a low-cost TDR circuit. Soil salinity is highly variable under both furrow and drip irrigation systems in regions where water quality is low, and this causes the frequency domain (capacitance) sensors to give erroneously high readings, over estimating the soil water content and leading to under irrigation. The sensors selected for accuracy assessment included the Acclima (ACC) time domain transmission sensor (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. |
