Soil C erosion and burial in cropland

Authors


  • Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Correspondence: A. J. VandenBygaart, tel. + 1 613 759 1836, fax + 1 613 759 1929, e-mail: bert.vandenbygaart@agr.gc.ca

Abstract

Erosion influences the lateral and vertical distribution of soil in agricultural landscapes. A better understanding of the effects of erosion and redistribution on soil organic carbon (C) within croplands would improve our knowledge of how management practices may affect global C dynamics. In this study, the vertical and lateral distribution of soil organic C was characterized to evaluate the amounts and timescales of soil organic C movement, deposition and burial over the last 50 years in different agroecosystems across Canada. There was strong evidence that a substantial portion of eroded sediment and soil organic C was deposited as colluvium close to its source area, thereby burying the original topsoil. The deepest aggraded profile was in a potato field and contained over 70 cm of deposited soil indicating an accumulation rate of 152 Mg ha yr−1; aggraded profiles in other sites had soil deposition rates of 40–90 Mg ha−1 yr−1. The largest stock of soil organic C was 463 Mg ha−1 (to 60 cm depth) and soil C deposition ranged from about 2 to 4 Mg ha−1 yr−1 across all sites. A distinct feature observed in the aggraded profiles at every site was the presence of a large increase in soil organic C concentration near the bottom of the A horizon; the concentration of this C was greater than that at the soil surface. Compared to aggraded profiles, the SOC concentration in eroded profiles did not differ with depth, suggesting that dynamic replacement of soil organic C had occurred in eroded soils. A large amount of soil organic C is buried in depositional areas of Canadian croplands; mineralization of this stock of C appears to have been constrained since burial, but it may be vulnerable to future loss by management practices, land use change and a warming climate.

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