Influence of tillage practice on carbon sequestration is scale-dependent

While the influence of management practices on soil organic C (OC) concentration and mass has been evaluated for the surface layer of small plots of homogeneous soils, there are few studies at a scale inclusive of the entire solum and heterogeneous soils. The objective of this study was to test for an interaction between tillage practice [no-till (NT) vs, conventional tillage (CT) by chisel-plow] and topography as determinants of OC stocks in the entire solum and layers thereof at a field-scale. Adjacent fields of contrasting tillage practice were stratified by soil series and drainage class for comparison. The effect of tillage practice on OC mass was contingent on slope position and sampling depth, i.e., scale-dependent. There was more OC in the surface layer (0-8 cm) of the A horizon of the NT than the CT field at well-drained upper slope positions, but not at imperfectly drained lower slope positions. At lower slope positions there was more OC in the entire A horizon of the CT than the NT field. Results of small-plot studies with homogeneous soils cannot be extrapolated arbitrarily to larger scales. Rather, assessments at larger scales that encompass heterogeneous soils are required.