Comparing Effects of Granular and Oil-Emulsion PAM On Soil Erosion, Water Infiltration, and Yields of Furrow Irrigated Crops.

Water soluble anionic polyacrylamide (WSPAM) is an important tool employed by producers to reduce erosion associated with furrow irrigation.  Two formulations of WSPAM are used in agriculture, although few if any reports comparing their effectiveness are published.  A long-term field study was conducted to compare the efficacy of two WSPAM formulations, a granular or solid form (A110) and the inverse emulsion or oil-based liquid form (A1883), for controlling erosion, maintaining infiltration, and improving silage corn and edible bean yields on furrow irrigated, silt loam soil with 1.5% slope.  Control, granular, and emulsion WSPAM treatments were applied to irrigation water supplied to plot furrows during each irrigation from 1993 to 1999.  Stock solutions prepared from granular and emulsion WSPAMs and tap water were injected into furrow inflows at 10 mg L^-1 only during furrow advance.  During irrigations, furrow inflow and runoff rates, and runoff sediment concentrations were measured.  Crop yields were measured in five of the seven years.  Relative to control furrows, the granular and emulsion WSPAM treatments reduced runoff sediment loss equally well, decreasing soil losses by 84% per irrigation, and preventing the loss of 47.8 Mg soil ha^-1 over the 7-year period.  The yearly soil loss reductions produced by granular and emulsion WSPAM ranged from 66 to 99% and may reflect changes in the electrical conductivity of the irrigation water.  Although both treatments increased infiltration fraction during irrigation of newly formed furrows, the emulsion produced the greatest overall increase in water infiltration fraction - the proportion of applied irrigation water that infiltrated.  Crop yields from granular WSPAM plots were 11.2% greater than that of controls, suggesting that the cost of WSPAM applications may be recoverable.  While the two WSPAM formulations provide equivalent erosion protection, differences in infiltration effects, yield gains, product costs, and potential environmental impacts should be considered when selecting the formulation.