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United States Department of Agriculture

Agricultural Research Service

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

Authors
item Entry, James - LOXAHATCHEE NAT'L WILDLIF
item Sojka, Robert

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 2007
Publication Date: March 19, 2008
Citation: Entry, J.A., Sojka, R.E. 2008. Carbon and nitrogen stable isotope ratios can estimate anionic polyacrylamide degradation in soil. Geoderma. 145:8-16.

Interpretive Summary: Water soluble anionic polyacrylamide (PAM) is a highly effective erosion-preventing and infiltration-enhancing polymer, when applied in furrow irrigation water. PAM degradation has not directly been measured in soil or water. Natural abundance of the carbon isotope ratios correlated with anionic PAM concentration in Xeric Haplocalcid and Typic Torripsamment soils but not Typic Kandiudult or Xeric Argialboll soils. Natural abundance of the nitrogen isotope ratios correlated with anionic PAM concentration in positive curvilinear relationships in Durinodic Xeric Haplocalcid and Typic Torripsamment soils and but not in Typic Kandiudult or Xeric Argialbolls soils. When 2691 kilograms PAM hectare was applied to the Xeric Haplocalcid soil, we measured 1317 kilograms PAM hectare in 2000 indicating 49% was degraded after 4 years and in 2006 we measured 691 kilograms PAM hectare indicating 74% of the PAM was degraded after 7 years. When 5382 kg ai PAM/ha-1 was applied to the Xeric Haplocalcid soil, we measured 4675 kilograms PAM hectare in 2000 indicating 13% was degraded after 6 years and in 2006 we measured 1466 kilograms PAM hectare indicating 73% of the PAM was degraded after 12 years We calculated PAM degradation rates based on carbon natural abundance ratios to be 9.8%/yr-1. Further testing using labeled anionic polyacrylamide is necessary to determine what portion of carbon released from decomposing PAM is incorporated into soil organic matter or living microbial biomass and being detected in the isotope ratio analysis and interpreted as PAM in remaining in soil.

Technical Abstract: Water soluble anionic polyacrylamide (PAM) is a highly effective erosion-preventing and infiltration-enhancing polymer, when applied at rates of 1 to 10 g/m-3 in furrow irrigation water. PAM degradation has not directly been measured in soil or water. Natural abundance of the carbon (13C/12C) isotope ratios correlated with anionic PAM concentration in positive curvilinear relationships in Xeric Haplocalcid and Typic Torripsamment soils r2 = 0.98 and 0.99 respectively) but not Typic Kandiudult or Xeric Argialboll soils r2 = 0.26 and 0.32 respectively). Natural abundance of the nitrogen (15N/14N) isotope ratios correlated with anionic PAM concentration in positive curvilinear relationships in Durinodic Xeric Haplocalcid and Typic Torripsamment soils and (r2 = 0.85 and 0.92 respectively) but not in Typic Kandiudult or Xeric Argialbolls soils (r2 = 0.55 and 0.45 respectively). When 2691 kg PAM/ha-1 was applied to the Xeric Haplocalcid soil, we measured 1317 kg ai PAM/ha-1 in 2000 indicating 49% was degraded after 4 years and in 2006 we measured 691 kg ai PAM/ha-1 indicating 74% of the PAM was degraded after 7 years. When 5382 kg ai PAM/ha-1 was applied to the Xeric Haplocalcid soil, we measured 4675 kg ai PAM/ha-1 in 2000 indicating 13% was degraded after 6 years and in 2006 we measured 1466 kg ai PAM/ha-1 indicating 73% of the PAM was degraded after 12 years. We calculated PAM degradation rates based on 13C decay to be 9.8%/yr-1. Further testing using 14C or 13C labeled anionic polyacrylamide is necessary to determine what portion of the 13C released from decomposing PAM is incorporated into soil organic matter or living microbial biomass and being detected in the isotope ratio analysis and interpreted as PAM in remaining in soil.

Last Modified: 7/23/2014
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