Polyacrylamide and water quality effects on infiltration in sandy loam soils

Slow infiltration rates constrain effective and economical irrigation in some sandy loam soils in California. Polyacrylamide (PAM) has increased soil infiltration in some areas, especially in soils high in clay or silt. Field trials near Fresno, CA, with PAM failed to show improved infiltration. Laboratory experiments were conducted to investigate PAM effect on infiltration of various quality waters in sandy loam soils. Two formulations of a high molecular weight PAM, a liquid emulsion and a granular, were evaluated on a Hanford sandy loam soil (coarse-loamy, mixed, superactive, nonacid, thermic Typic Xerorthents) in packed soil column experiments. Applying PAM continuously in the infiltration water always decreased infiltration for all PAM concentrations tested (5-20 mg PAM L-1). Final infiltration rates of 5 mg PAM L-1 relative to infiltration rate of deionized water were 65% for emulsion PAM and 36% for granular PAM and these ratios decreased with increasing PAM concentration. Reduction of infiltration rates when PAM was applied with water containing Ca (applied as gypsum) was less than with PAM solution containing Na. Permeability tests of PAM solutions through uniform sands showed a decrease of permeability with increased concentrations, due to an apparent increase in effective viscosity of the solution. The decrease in infiltration rates in this study was likely due to this increase in viscosity when PAM is added to water. This research concluded that PAM applied in irrigation water will reduce infiltration unless the material improves surface soil aggregate structure and sustains pores sufficient to mask the effect of solution viscosity.