POLYACRYLAMIDE AS AN ORGANIC NITROGEN-SOURCE FOR SOIL-MICROORGANISMS WITH POTENTIAL EFFECTS ON INORGANIC SOIL-NITROGEN IN AGRICULTURAL SOIL

Linear polyacrylamide(PAM) is gaining considerable acceptance as an ef fective anti-erosion additive in irrigation water. The potential effec ts of repeated PAM application on soil microbial ecology and the poten tial for biotransformation of this polymer in soils are not completely known. Untreated and PAM-treated soils (coarse-silty, mixed, mesic Du rixeroilic Calciorthids) were collected from agricultural fields near Kimberly, ID. Soils were analyzed to determine the effects of PAM trea tment on bacterial counts and inorganic N concentrations and the poten tial for PAM biotransformation. Culturable heterotrophic bacterial num bers were significantly elevated in PAM-treated soil for the plot plan ted to potatoes; this effect was not observed in the plot planted to d ry pink beans. Total bacterial numbers, determined by AODC, were not a ltered by PAM treatment in any of the soils sampled. Polyacrylamide-tr eated soil planted to potatoes contained significantly higher concentr ations of NO3- and NH3 (36.7 +/- 2.20 and 1.30 +/- 0.3 mg kg(-1), resp ectively) than did untreated soil (10.7 +/- 2.30 and 0.50 +/- 0.02 mg kg(-1), respectively). For bran held soil there was no difference betw een treated and untreated soil inorganic N concentrations. Enrichment cultures generated from PAM-treated and untreated soils utilized PAM a s sole N source, but not as sole C source. While the monomeric constit uents of PAM, acrylamide and acrylic acid, both supported bacterial gr owth as sole C source, the PAM polymer did not. Enrichment cultures th at used PAM for N exhibited amidase activity specific for PAM as well as smaller aliphatic amides. Utilization of PAM for N, but not for C, indicates that ultimately PAM may be converted into long chain poly ac rylate, which may be further degraded by physical and biological mecha nisms or be incorporated into organic matter. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.