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Force Abstract

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Effect of Afforestation on Aggregation and Particulate Organic Matter Carbon. J. Six, S.J. Morris, K. Paustian, E.A. Paul. ASA meeting, Salt Lake City (1999).

It is generally assumed that afforestation will lead to a sequestration of carbon. However, the processes resulting in a sequestration of carbon in afforested soils are still elusive. We hypothesized that the increase in aggregation with afforestation would lead to a higher physical protection and consequently an accumulation of carbon. At three sites in Ohio, forest, afforested and cultivated soils were sampled by horizon. Light, heavy and total particulate organic matter C (LPOM, HPOM, TPOM) were determined by dispersion and density floatation. Four aggregate size classes were separated by wet sieving and analyzed for organic C. At all sites, organic C concentration increased with increased aggregate size. At two of the three sites, LPOM of the A-horizon increased in the order: cultivated < afforested < forested. However, HPOM counterbalanced the increase in LPOM at one of these two site. Consequently, we observed at only one site a higher total POM C concentration in the afforested soil than the agricultural soil. In contrast, in the A-horizon of all sites, we observed higher proportions of large macroaggregates in afforested soils compared to cultivated soils. These data indicate that afforestation leads to an increase in structural stability, but that this structural stability does not always result in a sequestration of particulate organic matter C.