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SPECIAL SECTION: SOIL WATER SENSING

Calibration of a Capacitance System for Measuring Water Content of Tropical Soil

Department of Natural Resources and Environmental Management, University of Hawaii, 1910 East-West Road, Honolulu, HI 96822
^* Corresponding author (viktor{at}hawaii.edu)

Received 22 February 2005.

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 (R² = 0.96 and 0.97 for soil and sand, respectively) than the rangeland (R² = 0.73) and cultivated soils (R² = 0.74). The manufacturer default model fitted the field data reasonably well in the higher moisture range (0.35–0.45 cm³ cm^–3). However, it performed poorly in the dryer range (0.2–0.35 cm³ 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 R² = 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.

Abbreviations: MCS, multisensor capacitance system • TDR, time domain reflectometry

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				S. R. Evett and G. W. Parkin Advances in Soil Water Content Sensing: The Continuing Maturation of Technology and Theory Vadose Zone J., November 11, 2005; 4(4): 986 - 991. [Abstract] [Full Text] [PDF]