Monday, 10 July 2006

Carbon Sequestration in Soils of the Mississippi Valley Loess Plains.

Paula Gale, Richard Joost, Matt Goddard, and Kevin Smith. Univ of Tenneessee at Martin, 256 Brehm Hall, Martin, TN 38238

The deep loess soils of the Mississippi Valley Loess Plains provide a unique environment in which both climate and parent material are constants in soil development. Under these conditions land use and management, topography and time become the driving factors for carbon sequestration. Previous studies have shown that carbon stored in the soil as organic matter is of greater global significance than that stored as standing biomass. An understanding of the impact of land use on carbon sequestration can be used to develop management recommendations to enhance carbon storage. This information can also be used to develop predictive models that can form the foundation of valuation tools for application of a carbon credit program in the region. The objectives of the current study were to investigate the effect of land use on carbon storage, as Soil Organic Matter (SOM), and to develop a carbon budget for this ecosystem. Surface soil samples were collected from a variety of land uses throughout the region and analyzed for total soil organic matter and labile or reactive soil organic matter pools. Total soil organic matter was determined using both total combustion (CNS analyzer) and partial combustion (loss on ignition) techniques. Labile carbon pools were evaluated using both incubations and mild chemical oxidation techniques. Preliminary evaluation of the data indicated that upland landscape positions (46.7 16.4 g SOM kg-1 soil) had significantly higher soil organic matter levels than alluvial landscape positions (16.5 4.5 g SOM kg-1 soil). However, it was further noted that the alluvial locations sampled were also more intensely cultivated and it is suspected that further sampling and data analysis will allow us to qualify this difference. Our results have also indicated that time of year was not a significant factor in amassing soil organic matter. An expected flush of labile carbon through the landscape following crop senescence was not observed. This has left land-use and management as the most significant aspects contributing to soil organic matter levels, with native vegetation providing the highest levels of soil organic matter accumulation. Data collected from a plant succession study showed an increase in soil organic matter levels of 4.5 g kg-1 yr-1 (r2=0.95) during the first 5 years following elimination of pasture maintenance. The carbon budget being developed considers standing biomass, labile and recalcitrant soil organic matter pools. This carbon budget indicates that there is potential for annual storage of 5 Mg C ha-1 as organic matter in these soils. With cropland accounting for greater than fifty percent of farmland in this region, increasing carbon sequestration through land use modification can be significant.

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