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Soil N Dynamics Related to Soil C and Microbial Changes During Long-Term Incubation

Paul, Eldor A.1; Follett, Ronald F.2; Haddix, Michelle3; Pruessner, Elizabeth2

doi: 10.1097/SS.0b013e31822ce6e8
Technical Article

Knowledge of the pools and fluxes of C and N soil components is required to interpret ecosystem functioning and improve biogeochemical models. Two former grassland soils, where wheat or corn are currently growing, were studied by kinetic analysis of microbial biomass C and N changes, C and N mineralization rates, acid hydrolysis, and pyrolysis. Nearly twice as much C as N was mineralized during incubation. Modeling of changes during incubation demonstrated that two-pool first-order kinetics effectively described losses of microbial biomass C and N and concurrent N mineralization. Loss of microbial biomass N during incubation accounted for a significant portion of the N mineralized. Microbial biomass N content and soil N mineralization rates were strongly affected by soil type and soil management. Nitrification, but not N mineralization, was inhibited during the latter stages of incubation in one of the soils. We believe nitrifier populations had dropped below effective levels. Nonacid hydrolysable C was increased in both amount and mean residence time by cultivation and incubation. Hydrolysis removed a larger amount of N than incubation. Data after pyrolysis of soils, in argon at 550°C, closely reflected results for both C and N found after cultivation and incubation. This technique should be further investigated to identify the recalcitrant forms of C and N in soils. The dynamics of soil C and soil N, although related, are not identical; thus, management can be targeted to soil C or N cycling in ecosystem functioning or to soil organic matter dynamics in global change.

1Natural Resource Ecology Laboratory and Department of Soil and Crop Sciences, 200 W. Lake, Colorado State University, Fort Collins, CO 80523-1499. Dr. Eldor A. Paul is corresponding author. E-mail: eldor@nrel.colostate.edu

2USDA-ARS, Fort Collins, CO.

3Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO.

Received February 2, 2011.

Accepted for publication July 8, 2011.

Financial Disclosures/Conflicts of Interest: This study was supported in part through funded grants by the Office of Research (BER), US Department of Energy, and the NSF Division of Environmental Biology and is based on work supported by the Agricultural Research Service under the ARS, GRACEnet Project. The authors report no conflicts of interest.

© 2011 Lippincott Williams & Wilkins, Inc.