Fractal geometry and geostatistics for describing the field variability of soil aggregation

Fractal geometry has become a widely accepted descriptive tool for specific physical properties of natural soils and fractal scaling has recently been proposed as a model for soil particle size distribution. In this work, the cumulative mass distribution of dry soil aggregates, M(r < R), was estimated and shown to be proportional to R3-D, where r is the aggregate size, R is a specific measuring scale and D is the fractal dimension, which is a measure of soil fragmentation: the larger its value, the greater the fragmentation. Aggregates were collected from a depth of up to 40 cm of a clay soil located at Metaponto (South Italy). The field of 23 x 25 m was sampled in 81 sites at the nodes of a semi-regular grid and aggregate size distribution was obtained by dry sieving the soil through a nest of sieves (sized 10, 5, 2, 1 and 0.5 mm). The estimated D values were found to vary from 2 to 3 and were then interpolated by using the geostatistical procedure called ordinary kriging. The results were shown in the form of grey-coloured maps, which could be used as a useful tool for describing field variability in soil aggregation. (C) 1999 Silsoe Research Institute.