|Ajwa, Husein - UC DAVIS|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 22, 2005
Publication Date: February 27, 2006
Citation: Ajwa, H.A., Trout, T.J. 2006. Polyacrylamide and water quality effects on infiltration in sandy loam soils. Soil Science Society of America Journal, Vol. 70:643-650. Interpretive Summary: Some soils are difficult to irrigate efficiently and effectively because of low water infiltration rates. Polyacrylamide has been shown to increase infiltration in erodible silt loam soils. Field tests in sandy loam soils in the California San Joaquin Valley that sometimes have inadequate infiltration showed that polyacrylamide does not increase infiltration in these soils. Laboratory tests showed that, unless polyacrylamide reduces soil aggregate breakdown and surface seal formation, it will cause a decrease in infiltration. Thus, polyacrylamide should not be used to increase infiltration under conditions when soil erosion does not occur.
Technical Abstract: 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. However, 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 into sandy loam soils. Two formulations of a high molecular weight PAM, a powder (Pristine®) and a liquid emulsion (Superfloc®), were evaluated on Hanford sandy loam soil (coarse-loamy, mixed, thermic Typic Durixeralf) in column experiments. In the packed soil column experiments, applying PAM continuously in the infiltration water always decreased infiltration for all PAM concentrations tested (5 to 20 mg PAM L-1). Infiltration rates of >5 mg PAM L-1 solutions relative to infiltration rate of DI water were 65% for Pristine® and 36% for Superfloc®. Reduction of infiltration rates when PAM was applied with water containing Ca (applied as gypsum) was less than with water containing Na or DI water. 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 the column experiments and field studies 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.