SOIL AGGREGATES AS MASS FRACTALS

Soil aggregates have a fractal mass. That is, they are porous and, as they are studied in greater detail, more pores may be observed. Mass f ractals have scale-dependent bulk density. Larger objects, or soil agg regates, have a smaller bulk density. Bulk density in soil studies is sometimes assumed to be constant. If this was the case, soil aggregate s would not be mass fractals, and their porosity would not change with scale. The fact that soil aggregates are mass fractals places restric tions on the estimation of the fragmentation fractal dimension (D-f) o f soil. The mass fractal dimension of soil (D-m) may be calculated fro m bulk density-aggregate size data. Linear and nonlinear methods of es timating D-m were compared and were shown to give similar results. The D-m is shown to influence porosity and the saturated water content. F ractal theory, in particular D-m, has implications for the calculation of the pore-size distribution and the moisture characteristic. By equ ating Campbell's (1985) Version of the Brooks-Corey water retention fu nction, theta proportional to Psi((-1/b)), and an equivalent form to t he Brooks-Corey relation given by Crawford (1994), theta proportional to Psi((Dm-d)). it is suggested that D-m = d - 1/b, where d is the emb edding dimension.