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

Document Type

Article

Publication Title

Vadose Zone Journal

Abstract

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.

First Page

1004

Last Page

1010

DOI

10.2136/vzj2005.0028

Publication Date

11-1-2005

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