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Performance Analysis of Capacitance and Electrical Resistance-Type Soil Moisture Sensors in a Silt Loam Soil

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

Citation:  Transactions of the ASABE. 58(3): 649-665. (doi: 10.13031/trans.58.10761) @2015
Authors:   Daran R. Rudnick, Koffi Djaman, Suat Irmak
Keywords:   Capacitance probe, Electrical resistance sensors, Neutron gauge, Soil moisture sensors, Soil water retention curve, Water content.

Abstract. The performance of the Irrometer 200SS Watermark granular matrix sensor (WM), John Deere Field Connect (JD-v2) probe, and Delta-T PR1-capacitance (PR1-C) probe were evaluated against a Troxler 4302 neutron gauge (NG) for in-season field volumetric water content (θv) measurements at two soil depths in a Hastings silt loam soil at the University of Nebraska-Lincoln/Institute of Agriculture and Natural Resources South Central Agricultural Laboratory (SCAL) near Clay Center, Nebraska. The performances of the sensors were investigated over three years (2011-2013) under various water, nutrient, and crop management practices. The WM sensors performed best when using a field-calibrated soil water retention curve (SWRC) [root mean square difference (RMSD) = 0.024 m3 m-3] as compared to a SWRC developed from a pedotransfer function (RMSD = 0.070 m3 m-3). The WM sensors using a previously developed SWRC for the experimental field resulted in RMSD values less than 0.05 m3 m-3 when compared to the NG-measured θv at all depths and years. The JD-v2 probes underestimated θv in the dry range and overestimated θv in the wet range, which resulted in regression slopes and intercepts for the 0.30 and 1.0 m soil depths that were significantly different from unity (i.e., 1.0) and zero (p0.05 < 0.05), respectively. However, the performance of the JD-v2 probes improved in 2013 from RMSD values of 0.066, 0.068, and 0.067 m3 m-3 when using the manufacturer’s calibration to 0.043, 0.033, and 0.038 m3 m-3 for the 0.30, 1.0 m, and pooled soil depths, respectively, after calibrating the JD-v2 probes using the 2012 regression responses. The PR1-C probe-estimated θv regression coefficients were also significantly different from unity and zero (p0.05 < 0.05), respectively, and the resulting RMSD values ranged from 0.077 to 1.133 m3 m-3. In general, the WM and JD-v2 sensors followed the NG total water (TW) trends at all irrigation levels; however, the PR1-C probe was inconsistent and at times estimated unrealistic TW amounts. While there are limitations and concerns for each sensor technology, the results suggest that the WM and JD-v2 sensors can be used to monitor soil moisture to enhance irrigation management following field calibrations. Furthermore, development of soil-specific field calibration curves for individual soil depths is strongly recommended to enhance the performance of each sensor type and improve the accuracy of in-season field θv measurements.

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