Influence of tillage practice on carbon sequestration is scale-dependent

While the influence of management practices on soil organic C (OC) concentr ation and mass has been evaluated for the surface layer of small plots of h omogeneous 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 till age (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 contr asting tillage practice were stratified by soil series and drainage class f or 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 lowe r 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. Rath er, assessments at larger scales that encompass heterogeneous soils are req uired.