Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2002
Publication Date: 9/1/2002
Citation: BOSCH, D.D. VALIDATION OF CAPACITANCE BASED SOIL-WATER PROBES FOR COASTAL PLAIN SOILS. ASAE ANNUAL INTERNATIONAL MEETING. #022149. 2002. 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 soil-water levels in field soils. 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%. Additional work is required to evaluate better equations for absolute prediction of soil-water with these instruments.
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 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. Laboratory and field tests indicate that the probes track changes in soil-water and yield adequate relative estimates of soil-water. In most cases, the factory calibration was within +/- 50% of the observed soil-water. Results indicate improved relationships could be developed through laboratory tests. These probes should prove to be a useful tool for estimating soil-water in many Coastal Plain soils. However, additional work is required to evaluate better equations for absolute prediction of soil-water.