Methane flux in cropland and adjacent riparian buffers with different vegetation covers

Received for publication September 12, 2008. While water quality functions of conservation buffers established adjacent to cropped fields have been widely documented, the relative contribution of these re-established perennial plant systems to greenhouse gases has not been completely documented. In the case of methane (CH4), these systems have the potential to serve as sinks of CH4 or may provide favorable conditions for CH4 production. This study quantifies CH4 flux from soils of riparian buffer systems comprised of three vegetation types and compares these fluxes with those of adjacent crop fields. We measured soil properties and diel and seasonal variations of CH4 flux in 7 to 17 yr-old re-established riparian forest buffers, warm-season and cool-season grass filters, and an adjacent crop field located in the Bear Creek watershed in central Iowa. Forest buffer and grass filter soils had significantly lower bulk density (P < 0.01); and higher pH (P < 0.01), total carbon (TC) (P < 0.01), and total nitrogen (TN) (P < 0.01) than crop field soils. There was no significant relationship between CH4 flux and soil moisture or soil temperature among sites within the range of conditions observed. Cumulative CH4 flux was –0.80 kg CH4–C ha–1 yr–1 in the cropped field, –0.46 kg CH4–C ha–1 yr–1 within the forest buffers, and 0.04 kg CH4–C ha–1 yr–1 within grass filters, but difference among vegetation covers was not significant. Results suggest that CH4 flux was not changed after establishment of perennial vegetation on cropped soils, despite significant changes in soil properties.

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