Laboratory and Field Calibration of the Diviner 2000 Probe in Two Types of Soil

Abstract

The aim of this study was to calibrate the Diviner 2000 capacitance probe in the field and in the laboratory. Field calibration was carried out on an agro-forestry farm with soil of colluvial origin with two textural horizons, clay loam overlying clay. The same soil was used for laboratory calibration at the Universidad de Chile. Prior to calibration, the Diviner 2000 probe was normalized to obtain the scaled, or standardized, frequency (SF). For each method of calibration, three sets of soil moisture conditions were generated: dry, moist and saturated, with two replicates per set. The soil was evaluated with the probe at two depths per horizon, and the volumetric water content (θ) was immediately determined gravimetrically in situ at each depth. To calibrate the probe, the θ values for the samples were compared with the SF values recorded by the probe and the coefficient of determination was determined through regression analysis. A nonlinear correlation was found between the SF measured by the probe and the θ values obtained through gravimetry for each horizon and method of calibration, with adjustment to a potential function with a high coefficient of determination (field: R2=0.77; laboratory: R2=0.98). The manufacturer’s calibration equation proved to be quite precise in laboratory conditions, but in field conditions it underestimated the water content of both clay loam and clay soil.