Using a sequential density and particle-size fractionation to evaluate carbon and nitrogen storage in the profile of tilled and no-till soils in eastern Canada

Gregorich, E. G., Carter, M. R., Angers, D. A. and Drury, C. F. 2009. Using a sequential density and particle-size fractionation to evaluate carbon and nitrogen storage in the profile of tilled and no-till soils in eastern Canada. Can. J. Soil Sci. 89: 255-267. Tillage influences the retention and storage of organic matter (OM) in soil. We used a sequential density and particle-size fractionation to evaluate the total quantity and distribution of organic carbon (C) and nitrogen (N) in the profile of soils under mouldboard ploughing and no-till. Cores (0-60 cm) from four long-term tillage studies (in Prince Edward Island, Quebec, and two sites in Ontario) on soils of different textures, from sandy loam to clay were collected and divided into six depth increments. Four soil OM fractions were isolated on the basis of size and density from each sample. At two sites the standing stocks of C and N were larger in tilled than in no-till soil profiles at depths slightly greater than plough depth; tillage effects were also evident at a third site, where the mass of C in a layer close to the depth of ploughing was greater in tilled soils. Ploughing also had a substantial and consistent positive effect in all four soils on the quantity of C (and in some cases N) protected within aggregates, particularly at or near the bottom of the plough layer, and sometimes in surface soil layers. The differences in whole soil C and N between tilled and no-till systems can be attributed mostly to differences in mineral-associated OM, particularly in soils with heavier textures; but the other size and density fractions could together account for as much as 25% of the difference. Because the C capacity level was not reached in soils with heavy-texture, the potential for further accumulation Of C in these soil profiles is greater than that for soils with coarse-texture.