Calibration of a capacitance system for measuring water content of tropical soil

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Vadose Zone Journal


Capacitance sensors have improved substantially in the last decades, resulting in their wide acceptance. A new generation of multisensor capacitance systems (MCS) is now available that are easy to install and use. Calibration of capacitance sensors was conducted for a weathered clay loam soil and silica sand in field and laboratory conditions. The specific objectives of this research were to (i) conduct field and laboratory calibration of a new MCS in silica sand and soil, (ii) evaluate the performance of MCS for a shrinking-swelling tropical soil, and (iii) evaluate the effect of medium temperature on the MCS reading at constant water content. Three-parameter power type calibration equations were developed. The laboratory column calibration had higher correlation coefficients (R 2 = 0.96 and 0.97 for soil and sand, respectively) than the rangeland (R 2 = 0.73)and cultivated soils (R 2 = 0.74). The manufacturer default model fitted the field data reasonably well in the higher moisture range (0.35-0.45 cm 3 cm -3). However, it performed poorly in the dryer range (0.2-0.35 cm 3 cm -3), severely underestimating soil moisture content. Shrinking and swelling of soil and the presence of bound water might have affected the sensor's performance. Across the 45° C interval, there was 15% overestimation of the actual water content for soil and only 10% for sand. The relationship was statistically highly significant (P < 0.001) with an R 2 = 0.99 for both sand and soil. Use of MCS is suitable for tropical soil; however, site specific calibration is needed to improve the estimates of soil water content. © Soil Science Society of America.

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