| High molecular weight, linear, anionic polyacrylamide (PAM) is gaining considerable acceptance as an effective anti-erosion additive in irrigation water. Little is known regarding the potential impacts of repeated PAM application on soil microbiology.;I investigated the impact of PAM treatment on soil inorganic N pools, population levels of cultural heterotrophs, total numbers of bacteria, and the ability of soil-derived enrichment cultures to utilize PAM as sole C or N source. I investigated the enzymatic mechanism by which bacterial enrichments were able to utilize PAM as a N source, and assayed for PAM-specific amidase activity in enrichment cultures and in field soils. In addition, I investigated whether PAM treatment of soil could potentially alter the fate of other coapplied agrochemicals, such as pesticides with similar amide bonds, N containing fertilizers, and non-amide pesticides.;Polyacrylamide application to soils was correlated with elevations in inorganic N pools, higher population levels of culturable heterotrophic bacteria, and more rapid desorption of the pesticide, 2,4-D. Polyacrylamide treatment of soil correlated with lower levels of decarboxylation of 2,4-D and lower mineralization of the pesticide, atrazine. The most obvious biological soil impact corresponding with PAM treatment is the apparent induction of a soil amidase that hydrolyzes the large PAM polymer. While the substrate specificity of this amidase is unclear, we determined that soils with increased PAM specific amidase activity did not hydrolyze three amide containing pesticides.;Enrichment cultures derived from PAM-treated and untreated field soils, were able to utilize PAM as a sole N source, but were unable to use PAM as a sole source of C. Bacterial enrichments, able to use PAM for N, exhibited intracellular and extracellular amidase activity, which hydrolyzed a variety of amides of differing MW. Amidase production by the enrichment cultures correlated with actual removal of N atoms from PAM and an increase in culture cell density. Similar PAM-specific amidase activity was elevated in PAM-treated field soil, relative to untreated soils. These data strongly support the notion that the mechanism of N removal from PAM is catalyzed by an amidase enzyme, both in enrichment cultures and in the field. |
