Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2004
Publication Date: 3/4/2004
Citation: Bosch, D.D. 2004. Comparison of capacitance-based soil water probes in coastal plain soils. Vadose Zone Journal 3:1380-1389(2004). Interpretive Summary: Soil-water content is an important soil characteristic, used to evaluate irrigation needs, runoff susceptibility, and plant available water. Soil-water dramatically influences infiltration and runoff and consequently water quality. Knowledge of the amount of water existing in the soil is critical to understanding these processes. This manuscript describes the testing of two instruments which can be used to measure volumetric soil-water levels under field conditions. The instruments were found to track relative changes in soil-water fairly well. However, the absolute values of the predicted soil-water differed from the actual values by as much as 50%. Equations were developed which improve the estimates for Coastal Plain Soils. This improves the utility of these instruments for collection of soil-water data.
Technical Abstract: Soil-water dramatically influences infiltration and runoff and consequently water quality. In-situ measurements of soil-water are critical for understanding hydrologic and water quality processes. Precise in-situ measurements of soil-water are sparse. However, many advances have recently been made in soil-water measurement techniques. In particular, instruments for estimating volumetric soil-water from measurements of soil electrical properties have become very popular. While the instruments have been shown to be good indicators of relative changes in soil-water, questions remain regarding their ability to yield quantitative estimates. Most of these techniques rely upon a limited set of calibration equations obtained through laboratory analysis of homogeneous soil materials (i.e. sand, silt, and clay). This paper describes a validation study of two capacitance based soil-water probes for a range of Coastal Plain soils. The probes measure the capacitive and conductive properties of the soil. These measurements are then related to soil-water through calibration equations. Two years of laboratory and field tests indicate the probes track changes in volumetric soil-water and yield adequate relative estimates of soil-water. In most cases, the factory calibration was within +/-25% of the observed soil-water. Results indicate improved relationships could be developed through laboratory tests and calibration. Calibration curves for three different Coastal Plain Soils were developed which improve the accuracy of the predictions. The capacitance probes should prove to be a useful tool for estimating volumetric soil-water in many Coastal Plain soils. However, additional work is required to evaluate better equations for absolute prediction of soil-water.