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United States Department of Agriculture

Agricultural Research Service

Title: Estimating Soil Water Retention Curves Using Texture Class Mean Values of Air Entry Pressure and Porosity.

item Williams, Robert
item Ahuja, Lajpat

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 29, 1995
Publication Date: N/A

Technical Abstract: The one-parameter model, 1n(psi=p+b(1ntheta+q), is based on the log-log form of the soil water retention curve, below the air-entry value of psi, and requires one known psi (theta) value and a generalized slope-intercept relationship (p and q). Given p and q values for a soil or group of soils, the known psi (theta) is used to calculate the only unknown parameter in the model - b, and hence, the entire psi (theta) function. Earlier we developed p and q values for four broad textural ranges. Here we show that for a texture class p equals the log of the mean air-entry pressure [i.e., p=1n(psib], while q equals the absolute value of the log of the mean effective porosity [i.e., q=1n(thetae)]. This relationship provides p and q values for 11 texture classes. Soil water content was estimated for several soils varying in texture. When p and q values based on psib and thetae were used estimation errors were equal to, or less than, the errors using the previously derived p and q values. Using either set of p and q values provides better estimates of soil water content than regression models based on texture and bulk density.

Last Modified: 4/22/2015
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