Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 17, 2000
Publication Date: N/A
Interpretive Summary: With increasing concerns about global climate change, it is important to understand how human activities influence the increase of greenhouse gases in the atmosphere. Methane is an important greenhouse gas that is rapidly increasing in the atmosphere, but a group of soil bacteria have the ability to consume methane. This study was undertaken to examine how agricultural activities influence methane cycling in the soils of central Iowa. Agricultural lands under many different management practices were examined including: chisel plowed, no-till, with and without swine manure, and with and without chemical nitrogen fertilization. For comparative purposes we also examined natural lands (including native and restored prairie, and a forest site) and a municipal landfill site. Our results support a major generalization arising from past work, namely that natural forest and grassland systems are net consumers of atmospheric methane. No simple characterizations of methane flux from agricultural systems can be made. Many of the agricultural systems we studied exhibited low rates of both methane consumption and production; and thus, can be considered as neutral with regard to their impact on atmospheric methane concentrations. However, rainfall can substantially impact methane consumption and production from the soil. In 1994, a year of more normal rainfall, only the agriculture lands with manure fertility were net producers of methane. The landfill site was a strong source of atmospheric methane, despite the small amount of land area represented by this land use. Land managers, policy makers and action agencies will find this information useful in the application of practices, development of legislation, and implementation of regulations to mitigate global climate change.
Technical Abstract: The role of natural and agricultural ecosystems in terms of their methane contributions to the atmosphere is uncertain. This study was conducted to quantify and compare methane fluxes from a variety of ecosystems in central Iowa. We investigated agricultural systems under different agricultural management practices, a hardwood forest site, native and restored prairies, and a municipal landfill. Flux measurements were obtained using a closed-chamber method, and measurements were compiled by sampling over the 1993 and 1994 growing seasons. In 1993 most of the agriculture sites were net methane producers with mean CH4 fluxes ranging from -0.02 g m**-2 to 3.19 g m **-2 over the 258 day sampling season, while the natural ecosystems were net methane consumers with mean seasonal flux rates ranging from -0.27 to -0.07 g m**-2 258 d**-1. In 1994 only the landfill and the agricultural site treated with broadcast swine manure were net methane producers while the remainder of the natural and agricultural ecosystems were net methane consumers with mean seasonal flux rates ranging from -0.43 to -0.008 g m**-2 271 d**-1. We hypothesize that the differences in methane or CH4 fluxes between the two years are due to differences in rainfall. Also, at the agricultural sites we observed no reduction of CH4 consumption activity as a result of NH4 application. Rather, there appeared to be a stimulation of CH4 consumption in response to fertilization. It is suspected that out-gassing of CH4 dissolved in the manure slurry was the underlaying mechanism for the net positive fluxes observed at the manure treated sites.