In ̄uence of polyacrylamide application to soil on movement of microorganisms in runo water$

Polyacrylamide (PAM) use in irrigation for erosion control has increased water in®ltration and reduced soil erosion. This has improved runo€ water quality via lower concentrations of nitrogen, phosphorous, and pesticides, and decreased biological oxygen demand. Since non-toxic high molecular weight anionic PAMs removed clay size sediment particles in ̄owing water, we hypothesized that PAM would e€ectively remove or immobilize microorganisms in ̄owing water. In an agricultural ®eld, we determined the ecacy of PAM-treatment of furrow irrigation water to remove several categories of microorganisms in the in ̄ow and runo€. Treatments were: (1) PAM application and a control; (2) three ̄ow rates; (3) two distances from the in ̄ow point; and (4) three times during each irrigation. After water traveled 1 m at 7.5 and 15.5 l minÿ1 , PAM-treatment reduced total bacterial and microbial biomass and total fungal biomass relative to the control treatment. After water traveled 40 m at 7.5, 15.5, and 22.5 l minÿ1 , PAM-treatment reduced algae, the numbers active and total bacteria, active and total fungal length, and total bacterial biomass, total fungal and microbial biomass relative to the control treatment. Although speci®c organisms were not identi®ed or monitored in this study, the results clearly have implications for controlling the spread of soil-borne plant pathogens and other classes of harmful organisms within and among ®elds via irrigation water and in re-utilized return ̄ows. Beyond furrow-irrigated agriculture, new methods to manage overland transmission of harmful microorganisms could potentially help control transport of pathogens from animal waste in runo€ and groundwater. Published by Elsevier Science Ltd.