CHANGES IN CRACKING, WATER-CONTENT, AND BULK-DENSITY OF SALINIZED SWELLING CLAY FIELD SOILS

Shrinkage and cracking characteristics of swelling clays at two sites under border strip irrigation were examined. At one site, irrigation w ater salinity was varied. Image analysis of soil surface photographs w as used to quantify surface ped geometry. Volumetric surface soil samp les were used to find temporal and spatial variation of water content and bulk density both on the surface and with depth. Qualitative obser vations of cracking behavior were made in the field. There was no spat ial dependence for water content and bulk density at the scale of seve ral centimeters or between peds. Larger, more polygonal peds were obse rved in higher salinity treatments, wheel traffic rows, and after repe ated irrigations. Surface shrinkage increased with salinity. Dry bulk density was higher on the high salinity treatment both on the surface and with depth. Despite larger area, perimeters of the 9000 ppm treatm ent peds were less than perimeters for other treatments. Surface perce nt crack area followed percent change in bulk density.