SALT DISTRIBUTIONS IN CRACKING SOILS AND SALT PICKUP BY RUNOFF WATERS

Detailed measurements were made of I:he levels and distributions of sa lts present in representative soil profiles and fields and associated tailwaters in the Imperial Valley of California. The findings showed t hat the potential salinity-pickup hazard may be greater in this valley that is dominated by cracking soils than classical theory would predi ct. Salts that would otherwise be ''isolated'' in seedbeds or leached downward during irrigations are more ''exposed to'' and ''picked up by '' the runoff water than previously recognized as a result of the flow of the irrigation water throughout the beds and horizontally in the t opsoil via the extensive network of cracks and fractures that form in the cracking soils. As a result, the pattern of salinity within the be ds of such soils is one-dimensional, rather than the expected, classic al two-dimensional pattern. Salt content in the tailwater associated w ith cracking soils was higher and sustained over longer periods of tim e than in the case of non-cracking soils.