SCALING OF SOIL-WATER RETENTION USING A FRACTAL MODEL

A quantitative description of the spatial variability of soil hydraulic properties is increasingly important, especially in simulations of soil water regimes. The objective of this study was to use a fractal concept to quantify and simulate the spatial variability of water retention of fine textured soils over a wide range of soil matric potentials. To scale water retention data, we assumed fractal self-similarity of pore volume and derived an equation of the water retention curve in the form of the probability integral. Experimental data on water retention were obtained on sand-kaoline plates and above saturated salt solutions in the ranges of the soil matric potential from -50 to -1 kJ m(-3) and from -140 to -20 MJ m(-3), respectively, for chernozem soil (Typic Haploboroll, clay loam) sampled over a 12,000 m(2) area and for dark chestnut soil (Ustolic Orthid, loam) sampled over a 1500 m(2) area. The resulting formulae gave a good fit of water retention data. The spatial variability of water retention could be described by the spatial variability of the single dimensionless parameter. Pore fractal dimension could be considered constant over the areas of sampling for both soils.