| Abstract:In order to quantitatively compare and calibrate measurement values in soil volumetric water content (VWC) of mainstream moisture sensors sold on the market in heavy saline soils,eight well-known sensors namely,EC-5,5TE,Teros12,Hydra-probe Ⅱ,TDR315L,TDR315H,TDR305H and CS655,were selected for the comparison and calibration of VWC measurement values.The typical heavy saline soil (total salinity content is 6.8 g·kg-1) for the experiment was collected from the coastal region of Rudong in Jiangsu Province. Soil samples of six soil moisture levels,0.20,0.25, 0.30,0.35,0.40 and 0.45 cm·cm-3,were prepared in acrylic columns.The results showed that the measured VWC of these eight sensors were all higher than the actual values to varying degree. In particular,all sensors except for EC-5 showed the phenomenon of distortion at a relative high VWCs. The distortion phenomenon could be summarized into two types, mutation type and insensitive type. CS655 showed mutation type distortion at all six soil moisture levels. Hydra-probe Ⅱ,5TE,TDR315L and TDR315H showed mutation type distortion at relatively high soil moisture and the threshold value was in the range of 0.35-0.40 cm·cm-3. Whereas,TDR305H and Teros12 showed insensitive type distortion after the soil moisture exceeds 0.40 cm·cm-3. When soil moisture was below the distortion threshold of each sensor,TDR315H and TDR305H performed the best with the least variation in measured values of soil moisture ,followed by Teros12,TDR315L,5TE,EC-5 and Hydra-probe Ⅱ. With the exception of the CS655,the other sensors were calibrated within the distortion threshold based on the original conversion equations. The accuracy of the measured VWC using the recalibrated equations could reach ±0.02 cm·cm-3. The results of this study can provide practical guidance and countermeasures for accurate and efficient measurement of soil moisture in heavy saline soils. |
