Mamedov, A.I., USDA-ARS-NPA-GMPRC-EWERU, Manhattan, KS 66502, United States
Shainberg, I., Agricultural Research Organisation, Volcani Center, Institute of Soils and Water, PO Box 6, Bet-Dagan, Israel
Wagner, L.E., USDA-ARS-NPA-GMPRC-EWERU, Manhattan, KS 66502, United States
Warrington, D.N., State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, CAS and MWR, Institute of Soil and Water Conservation, Yangling, Shaanxi Province 712100, China
Levy, G.J., Agricultural Research Organisation, Volcani Center, Institute of Soils and Water, PO Box 6, Bet-Dagan, Israel

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 dryland 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 (20kg/ha), with moderate (2 × 10 5 Da) or high (1.2 × 107Da) MW, mixed with phosphogypsum (PG) (4Mg/ha) affects infiltration rate, runoff, and erosion. Five smectitic soils, treated with PAM and PG, were exposed to simulated rainfall of deionised water in the laboratory. Both dry PAMs, mixed with PG, increased final infiltration rate (35 times) and reduced erosion (2-4 times) relative to the control (no amendments). Whereas the polymers' effects on the infiltration rate 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 840g/m 2, in the control, to 570 and 370g/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. © 2009 CSIRO.