Exchangeable ammonium and nitrate from different nitrogen fertilizer preparations in polyacrylamide-treated and untreated agricultural soils

High molecular weight, anionic polyacrylamide (PAM) is currently being used as an irrigation water additive to significantly reduce soil erosion assoc iated 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 potent ial impacts of PAM treatment on the rate at which fertilizer N is transform ed into NH4+ and NO3- in soil. PAM-treated and untreated soil microcosms we re amended with a variety of fertilizers, ranging from common rapid-release forms, such as ammonium sulfate [(NH4)(2)SO4] and urea, to a variety of sl ow-release formulations, including polymerized urea and polymer-encapsulate d urea. Ammonium sulfate was also tested together with the nitrification in hibitor dicyandiamide (DCD). The fertilizers were applied at a concentratio n of 1.0 mg g(-1), which is comparable to 100 Ib acre(-1), or 112 kg ha(-1) . Potassium chloride-extractable NH4+-N and NO3--N were quantified periodic ally during 2-4 week incubations. PAM treatment had no significant effect o n NH4+ release rates for any of the fertilizers tested and did not alter th e 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.