Williams, Robert  
Ahuja, Lajpat 
Submitted to: Agronomy Abstracts
Publication Type: Abstract Only Publication Acceptance Date: October 29, 1995 Publication Date: N/A Technical Abstract: The oneparameter model, 1n(psi=p+b(1ntheta+q), is based on the loglog form of the soil water retention curve, below the airentry value of psi, and requires one known psi (theta) value and a generalized slopeintercept 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 airentry 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.
