Gal, M., ARO. Volcani Center, Bet Dagan 50250, Israel.
Arcan, L., ARO. Volcani Center, Bet Dagan 50250, Israel.
Shainberg, I., ARO. Volcani Center, Bet Dagan 50250, Israel.
Keren, R., ARO. Volcani Center, Bet Dagan 50250, Israel.

The effect of soil sodicity and phosphogypsum treatment on the structure of the crust of two soils (sandy loam and clay soil) was studied using a SEM. In soils with no exchangeable sodium, aggregate breakdown and surface compaction by raindrops are the dominant mechanisms for crust formation. In soils with ESP values above 1.5, chemical dispersion of the soil clays (enhanced by the sodicity of the soil, the low electrolyte concentration in the rain, and the stirring effect of the raindrops) and the downward movement of the clays into the 'washed in' layer clogging the pores in this layer were the dominant mechanisms in crust formation. Soils with a 'washed in' layer had a very low infiltration rate. -from Authors