CHANGES IN SOIL POROSITY AND SURFACE SHRINKAGE IN A REMOLDED, SALINE CLAY SOIL TREATED WITH COMPOST

We studied modifications induced in soil porosity and in surface shrinkage in a saline clay soil treated with compost in laboratory trials, and we tested the effect of wetting and drying cycles. Porosity and pore size distribution were measured on thin sections prepared from soil samples by using electrooptical image-analysis (Quantimet 720). Shrinkage was measured on the surface of dried samples using the same apparatus. The application of wetting and drying cycles to the control samples first increased the proportion of pores ranging from 30 ±m to 1 mm in equivalent pore diameter to a maximum, and then these pores decreased steadily with further wetting and drying cycles. In treated samples the intra-aggregate porosity was higher than in control samples only after the first wetting and drying cycles; then it was always lower and at the end of the experiment decreased with respect to the beginning. Modifications of pore size distribution were also observed. The total surface shrinkage increased after wetting and drying cycles and in control samples was always higher than in treated samples but, at the end of the experiment, cracks were larger in treated samples. This unusual behavior of soil-compost interactions could be ascribed to the salinity of both soil and compost.