Long-term Polyacrylamide formulation effects on soil erosion, water infiltration, and yields of furrow-irrigated crops
Two formulations of water-soluble anionic polyacrylamide (WSPAM) are used in agriculture to reduce erosion and manage infiltration in furrow irrigations, although few if any reports have compared their effectiveness. A control and two WSPAMs, a granular form and the inverse emulsion, or oil-based liquid form, were applied to irrigation water supplied to furrows formed in a silt loam soil with 1.5% slope during each irrigation from 1993 to 1999. Stock solutions prepared from the two WSPAMs in tap water were injected into furrow inflows to attain a concentration of 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 7 yr. Relative to controls, both WSPAM treatments reduced runoff sediment loss equally well, decreasing soil losses by 84% per irrigation, and prevented the loss of 47.8 Mg soil ha–1 over the 7-yr period. The yearly soil loss reductions produced by WSPAMs ranged from 66 to 99%, and may reflect changes in the electrical conductivity (EC) of the irrigation water. Both WSPAM treatments increased the proportion of applied irrigation water that infiltrated into newly formed furrows, but the emulsion produced the greatest overall increase in water infiltration fraction. As a class, WSPAM treatments increased yields by 14.3% for bean (‘Viva Pink’ Phaseolus vulgaris L.) and 4.5% for silage corn (Zea mays L.), suggesting that the cost of WSPAM applications may be recoverable. While the two WSPAM formulations provide equivalent erosion protection, differences in infiltration effects, product costs, and potential environmental impacts should be considered when selecting the formulation.