Efficacy of dry granular anionic polyacrylamide (PAM) on infiltration, runoff and erosion

Seal formation at the soil surface during rainstorms reduces rain infiltration and leads to runoff and erosion. Surface application of dissolved polyacrylamide (PAM) mixed with gypsum was found to be effective in decreasing seal formation, runoff and erosion. Surface application of dry granular PAM mixed with gypsum was effective in decreasing runoff and erosion. However, surface application of dry granular PAM without a source of electrolytes was not effective in maintaining a good infiltration rate (IR), but was effective in preventing erosion. The objectives of this study were (i) to investigate the mechanisms by which granular PAM was effective in controlling erosion but was not effective in maintaining IR, (ii) optimize dry granular PAM dosage according to purpose of application and (iii) devise a practically viable method of applying dry PAM for improving IR and erosion control. Granular PAM-A110 (0, 5, 10 and 20kgha(-1)) spread on the surface of a silt loam soil (Calcic Haploxeralf) was exposed to three treatments (control; gypsum at the rate of 4Mg ha(-1); 40mm 0.02m CaCl2 mist and drying) and all received simulated rain of deionized water (DW). The initial IR of the control treatment was good but decreased to very small values after seal formation. The initial IR of the 20kgha(-1) dry PAM treatment was very small and remained small throughout the rain event. The IRs of the 5 and 10kgha(-1) dry PAM treatments were more than those of the 20kgha(-1) treatment. Whereas the small IR of the control was through seal formation, that of the dry PAM treatments resulted from PAM dissolution and the very large viscosity of the infiltrating PAM solutions. Mixing the PAM granules with gypsum or spraying the electrolyte solution and drying were effective in maintaining a large IR and a small erosion rate. The electrolytes in the infiltrating rain and drying of the wetted soil reduced the large viscosity of the PAM solution in the soil and increased the IR. Dissolved PAM in runoff increased the binding of surface soil particles by the PAM polymers, decreased soil particle detachment from the soil surface and increased the flocculation of the eroded soil particles. These processes were studied in connection with the extensive use of PAM in preventing furrow erosion.