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 water salinity was varied. Image analysis of soil surface photographs was used to quantify surface ped geometry. Volumetric surface soil samples were used to find temporal and spatial variation of water content and bulk density both on the surface and with depth. Qualitative observations of cracking behavior were made in the field. There was no spatial dependence for water content and bulk density at the scale of several centimeters or between peds. Larger, more polygonal peds were observed in higher salinity treatments, wheel traffic rows, and after repeated 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 treatment peds were less than perimeters for other treatments. Surface percent crack area followed percent change in bulk density.