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 (