AbstractHigh molecular weight, anionic polyacrylamide (PAM) is currently being used as an irrigation water additive to significantly reduce soil erosion associated with furrow irrigation. PAM contains amide-N, and PAM application to soils has been correlated with increased activity of soil enzymes, such as urease and amidase, involved in N cycling. Therefore we investigated potential impacts of PAM treatment on the rate at which fertilizer N is transformed into NH4+ and NO3 in soil. PAM-treated and untreated soil microcosms were amended with a variety of fertilizers, ranging from common rapid-release forms, such as ammonium sulfate [(NH4)2SO4] and urea, to a variety of slow-release formulations, including polymerized urea and polymer-encapsulated urea. Ammonium sulfate was also tested together with the nitrification inhibitor dicyandiamide (DCD). The fertilizers were applied at a concentration of 1.0mg g1, which is comparable to 100lb acrel, or 112kg ha1. Potassium chloride-extractable NH4+-N and NO3-N were quantified periodically during 24 week incubations. PAM treatment had no significant effect on NH4+ release rates for any of the fertilizers tested and did not alter the efficacy of DCD as a nitrification inhibitor. However, the nitrification rate of urea and encapsulated urea-derived NH4+-N was slightly accelerated in the PAM-treated soil.