POLYMER MOLECULAR-WEIGHT AND DEGREE OF DRYING EFFECTS ON INFILTRATIONAND EROSION OF 3 DIFFERENT SOILS

Low infiltration rate and high levels of soil erosion are critical pro blems in many soils worldwide. Amendment of soils with organic polymer s could alleviate these problems. The objective of the present study i s to investigate the effects of polymer molecular weight and the degre e of drying on the infiltration rate of, and erosion from, three diffe rent soil types from Israel. A solution of high-molecular-weight (2x10 (7) Da) or low-molecular-weight (2x10(5) Da) negatively charged polyac rylamide (PAM(H) and PAM(L), respectively) was added to the surface of soil samples packed in trays, at a rate of 20 kg ha(-1). The soil sam ples were allowed to dry to varying degrees and were then exposed to 6 0 mm of simulated rain during which infiltration rate and soil loss we re determined. The ability of the polymer to maintain high final infil tration rates (FIR) depended on its molecular weight and the clay cont ent of the soils. In the coarse- and medium-textured soils, the PAM(H) was more effective than the PAM(L) in maintaining high FIR. In the fi ne-textured soil, the effects of both polymers on Fm. were comparable; the use of the PAM(L) is therefore preferable since it is easier to h andle. Both polymers had reduced soil loss comparably. The effects of drying were similar for both polymers: the FIR and soil loss values wi th the intermediate degrees of drying were higher and lower, respectiv ely, than they were with the no-drying or complete-drying treatments.