Prediction of a pore distribution factor from soil textural and mechanical parameters
2001
Giménez, D. | Rawls, W. J. | Pachepsky, Y. | Watt, J. P. C.
Soil-water retention properties (WRC) are required for modeling purposes, but data availability is restricted by the high cost of measurements. Prediction of WRC from particle size distribution (PSD) is a useful approach that could be improved by accounting for soil structure. Mechanical parameters can characterize soil structure in situ. Our objective was to use mechanical and PSD parameters to estimate a pore distribution factor, λ, from a power-law model of WRC. Samples for WRC and PSD determinations were taken in pre-wetted horizons after characterization of soil structure with multiple measurements of a single-vane shear test (SB) and penetration resistance (PR). Mechanical parameters were the mean, M, and standard deviation, σ, of SB and PR. Parameters characterizing a PSD were the power exponent of a cumulative exponential function, β; the geometric mean, μ(r) = eln(r) and standard deviation, σln(r), of a log-normal distribution; and clay content. Models of λ were built with the Group Method of Data Handling (GMDH) first using textural and mechanical parameters separately and then using each textural variable with all mechanical parameters. Both μ(r) and σln(r) were consistently selected as the best textural estimators of λ. The best mechanical estimators were log(MSB) and σSB. In models that included textural and mechanical parameters, σPR was selected consistently regardless of the textural parameter used. Textural parameters were better predictors than mechanical parameters, even though the latter alone provided a reasonable estimate of λ. Mechanical parameters improved textural estimates of λ only when clay content was used to characterize a PSD.
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