The effect of dry granular PAM mixed with soil or gypsum on IR and erosion of soils exposed to distilled water rain was studied. The amendments had similar effects on a silty loam (loess soil) and sandy clay (vertisol). Spreading gypsum at the soil surface increased the IR and reduced runoff and erosion. Spreading dry PAM mixed with gypsum was very effective in increasing the IRs of the two soils and in reducing runoff and soil losses. Mixing dry PAM with soil was not effective in increasing IR and reducing runoff. However, this treatment was very effective in reducing soil losses. In dilute solutions, PAM chains adsorbed on the external surfaces of a soil particle are 0.1 to 0.2 mm in length, and therefore block the water-conducting pores while binding the particles together into a cohesive surface. The observed low IR is therefore due to a reduction in soil hydraulic conductivity rather than seal formation.

Mixing dry PAM with soil was most effective in preventing erosion, because it increased interparticle bonding due to the long polymer chains. Polyacrylamide mixed with gypsum also reduced erosion, but the mechanism was different. The high electrolyte concentration due to the presence of gypsum flocculated the clay particles, coiled the PAM chains, enhanced aggregation, and decreased seal formation. The combination of seals with high IR and stable aggregates reduced erosion. These results suggest that soil and water conservation in dryland farming in soils susceptible to sealing and erosion can be improved by spreading dry PAM mixed with gypsum on the soil surface

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