The Effects of Long-term Application of Organic Amendments on Soil Organic Carbon Accumulation

Application of organic amendments (e. g., biosolids[BS], composts) to soil may provide an effective method for accumulating considerable amounts of C, but the long term stability of such C is not well known. We investigated study sites in Virginia to determine the amounts of C remaining in soils 7 to 27 yr following amending with biosolids and composts. The first study employed a Fauquier silty clay loam (fine, mixed, active, mesic Ultic Hapludalf) to which four treatments (control, poultry litter-yard waste compost, biosolids compost, and poultry litter) were continuously applied during 2000-2004. The second study was conducted on a Davidson clay loam (fine, kaolinitic, thermic, Rhodic Kandiudult) to which six rates of aerobically digested biosolids (0, 42, 84, 126, 168, and 210 Mg ha(-1)) were applied in 1984. The third study was on a Pamunkey sandy loam (fine-loamy, mixed, semiactive, thermic Ultic Hapludalfs) to which five rates of anaerobically digested biosolids (0, 14, 42, 70, and 98 Mg ha(-1)), with and without sawdust, were applied in 1996. Total soil organic C concentration and bulk density were measured to calculate C accumulation. The organic amendment-treated soils increased C in the surface soil depth (<15 cm), ranging from 2 to 12% of C across all three sites. Soil C movement was limited to a depth of 15 cm. Evidence of C saturation was revealed in the third study site. These results demonstrate that organic amendments applied over a long time remain in soil and may contribute to C sequestration in the Mid-Atlantic region.