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Title: USING THE GREGSON ONE-PARAMETER MODEL TO ESTIMATE THE SOIL-WATER RETENTION.

Author
item Williams, Robert
item Ahuja, Lajpat

Submitted to: Soil Dynamics International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/26/2000
Publication Date: 6/15/2000
Citation: WILLIAMS, R.D., AHUJA, L.R. 2000. USING THE GREGSON ONE-PARAMETER MODEL TO ESTIMATE THE SOIL-WATER RETENTION. SOIL DYNAMICS INTERNATIONAL CONFERENCE PROCEEDINGS. Absract p. 9-B.

Interpretive Summary: Abstract Only.

Technical Abstract: The soil water retention, i.e., the relationship between the soil-water content and soil-matric potential, is one of the two basic soil hydraulic properties. However, the standard laboratory and field procedures used to determine the soil-water retention are tedious and time consuming. For this reason, several methods have been proposed to estimate the soil-water retention from simpler soil properties (e.g., texture and bulk density) and/or limited data. One approach is based on the log-log form of the soil water retention curve below the air-entry value of psi, requires one known value of psi(theta), and a general slope-intercept relationship (p and q), which provides the general form of the Gregson one-parameter model: ln (psi) = p + b(ln(theta) + q). Previously, values of p and q were developed for four broad textural ranges. Further work has shown that for a texture class p equals the natural log of the mean air-entry pressure, while q equals the absolute value of the natural log of the saturated water content. This relationship provides p and q values for 11 texture classes. When these p and q values were used, estimation errors were equal to, or less than, the errors using the previously derived p and q values. Both sets of p and q values provide better estimates of soil water content than the regression models based on texture and bulk density. Overall, the one- parameter function estimates the soil water retention curve fairly well, and provides a simple approach to estimate soil-water content.