Carbon and nitrogen stable isotope ratios can estimate anionic polyacrylamide degradation in soil

Water-soluble anionic polyacrylamide (PAM) is applied to millions of hectares worldwide as a highly effective erosion-preventing and infiltration-enhancing polymer, when applied at rates of 1 to 2 kg ha(-1) (i.e., 1 to 10 g m(-3)) in furrow water. PAM degradation has not directly been measured in soil. We tested the ability of stable isotopes of C and N at natural abundance to estimate PAM degradation rates. Values of delta C-13 were related to anionic PAM concentration in a positive curvilinear relationship in a low-C, low-N, Durinodic Xeric Haplocalcid (Portneuf series) soil. The other soils with higher organic C or N concentrations did not show significant relationships between PAM concentrations and delta C-13 values. The 615N values were not related to anionic PAM concentration in any of the soils tested. When 2691 active ingredient (ai) kg PAM ha(-1) was applied to the Durinodic Xeric Haplocalcid soil, 49% and 74% of the PAM was degraded after 6 and 12 yr respectively. When 5382 kg ai PAM ha(-1) was applied to the Durinodic Xeric Haplocalcid soil, 13% was degraded after 6 yr, and 73% of the PAM was degraded after 12 yr. We calculated PAM degradation rate based on delta C-13 for the Durinodic Xeric Haplocalcid soil to be 9.8% yr(-1). Further testing using labeled PAM is necessary to estimate degradation rates in higher C soils, and to determine what portion of the C is released from decomposing PAM is emitted to the atmosphere, incorporated into soil organic matter and living microbial biomass. (c) 2008 Published by Elsevier B.V.