Infiltration and Erosion in Soils Treated with Dry PAM of Two Molecular Weights and Phosphogypsum

Authors: Iliasson, Amrax; SHAINBERG, ISAAC - Volcani Center (ARO); Wagner, Larry; WARRINGTON, DAVID - Chinese Academy Of Sciences; LEVY, GUY - Volcani Center (ARO)

Submitted to: Australian Journal of Soil Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2009
Publication Date: 12/11/2009
Citation: Mamedov, A.I., Shainberg, I., Wagner, L.E., Warrington, D.N., Levy, G. 2009. Infiltration and Erosion in Soils Treated with Dry PAM of Two Molecular Weights and Phosphogypsum. Australian Journal of Soil Research. 47(8):788-795.

Interpretive Summary: Soil amendments such as gypsum and anionic polyacrylamide (PAM), both environmentally safe soil amendments, have been used to reduce soil erosion by wind and water. Water soluble PAMs are effective because they stabilize soil structure, prevent clay dispersion and improve soil clay flocculation. Gypsum is effective because, upon dissolution, it releases salts into the rainwater that prevent clay dispersion and thus reduce soil aggregate breakdown. The effectiveness of PAMs also depends on its molecular weight (MW) and soil properties. We investigated the effects of surface applied granular PAM (20 kg ha-1) of two molecular weights (medium and high) together with gypsum (4 Mg ha-1) on the infiltration rate, runoff and erosion from 5 soils ranging in texture from loamy sand to clay, during simulated rainstorms. Surface application of PAM (for both molecular weights) supplemented with gypsum resulted in up to four times the steady state infiltration rate when compared to the control treatment (no amendments applied). In addition, the combined treatments of PAM and gypsum also produced up to five times less runoff and erosion than the control treatment. The combined treatments also showed significant beneficial differences compared to the PAM and gypsum only treatments as well. PAM with moderate molecular weight was considerable more effective in reducing soil loss than PAM with high molecular weight. More studies, in which PAM with different molecular weight is applied in the form of dry granules, are needed in order to maximize the efficiency of PAM application in a soil-specific management approach to controlling soil and water losses.

Technical Abstract: Soil surface application of dissolved linear polyacrylamide (PAM) of high molecular weight (MW) can mitigate seal formation, runoff and erosion, especially when added with a source of electrolytes (e.g., gypsum). Practical difficulties associated with PAM solution application prohibited commercial use of PAM in dry land farming. An alternative practice of spreading dry granular PAM with high MW on the soil surface has been ineffective in reducing runoff while effectively reducing erosion. The objective of this study was to investigate the mechanism by which granular PAM (20 kg/ha), with moderate (2x105 Da) or high MW (1.2x107 Da), mixed with phosphogypsum (PG) (4 Mg/ha) affects infiltration rate (IR), runoff and erosion. Five smectitic soils, treated with PAM and PG, were exposed to simulated rainfall of deionized water in the laboratory. Both dry PAMs, mixed with PG, increased final IR (3 to 5 times) and reduced erosion (2 to 4 times) relative to the control (no amendments). Whereas the polymers' effects on the IR and runoff relative to each other were inconsistent, PAM with moderate MW was consistently more effective in reducing soil loss than PAM with high MW. For example, in the sandy clay soil, soil losses were reduced from 840 g/m2, in the control, to 570 and 370 g/m2 for the high- and moderate-MW PAM treatment, respectively. This greater capacity to control soil erosion was ascribed to the lower viscosity of the soil surface solution following dissolution of dry PAM granules in the case of moderate-MW PAM, leading to more uniform, effective treatment of soil aggregates at the soil surface by the polymer.