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item Tsegaye, T
item Tadesse, W
item Coleman, T
item Jackson, Thomas
item Tewolde, Haile

Submitted to: Canadian Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2004
Publication Date: 6/1/2004
Citation: Tsegaye, T.D., Tadesse, W., Coleman, T.L., Jackson,T.J., Tewolde, H. 2004. Calibration and modification of impedance probe for near surface soil moisture measurements. Canadian Journal of Soil Science. 84(2):237-243.

Interpretive Summary: A simple, fast and effective method to measure near-surface soil moisture content was developed and validated. The performance of the modified version of a commercially available impedance probe device in both the field and greenhouse experiments was very good and can meet the specified requirement. If the user develops and applies depth- and site- specific calibration curves, the instrument has great potential for detecting changes in the soil moisture content at 2, 3, and 5-cm soil depths. Furthermore, the instrument can also provide an estimation of near-surface soil moisture content within a 3% accuracy range to the values determined by the gravimetric technique. Soil moisture measurement at or near the soil surface with minimum sampling and measurement errors is important to relate ground-based measurements to remotely- sensed data. Soil moisture is a key element in agricultural, hydrological, and climatic systems. The spatial and temporal variability of soil moisture directly affects plant growth and crop yields. They also impact the water and energy cycles of the earth. Thus, increasing the understanding and estimation of the space-time structure of soil moisture is essential to improve the predictability of soil moisture, which will lead to improved forecasts for agriculture and hydrology.

Technical Abstract: A reliable and low cost sensor that can measure soil moisture at or near the soil surface is currently not available. The objectives of this study were: (i) to evaluate the possibility of modifying an Impedance Probe (IP) to measure soil moisture content at a very shallow depth (2-5 cm); and (ii) to compare the soil moisture values obtained using the IP to the values obtained using the traditional gravimetric method. The research was conducted at the Winfred A. Thomas Agricultural Research Station (WTARS) Hazel Green, Alabama. The standard IP that is capable of measuring soil moisture content at 6-cm soil depth was modified to measure soil moisture at 2, 3, and 5 cm depths. Using a site and depth-specific calibration technique it provided results that were comparable to the values that were obtained following the traditional gravimetric water content determination protocol. We found that the instrument was very sensitive to changes in soil moisture content and has great potential as replacement for the gravimetric technique. It allows repetitive measurements of soil moisture content at a very shallow depth with minimal soil disturbance. Furthermore, the instrument is particularly valuable for providing ground- truth soil moisture contents to validate remotely-sensed data.