Spatial dependence of soil organic carbon mass and its relationship to soil series and topography

Concern about the global increase in atmospheric CO2 has focussed attention on C sequestration in soil and the influence of management practices on soil organic C (OC) stocks. Evaluation of management practices is required at scales comparable to farm management units, which encompass heterogeneous soils and different landforms. The objectives of this study were to describe the spatial dependence of soil OC mass in two adjacent fields with contrasting tillage practices on Black Chernozemic soils using geostatistics and relate it to topographic features and soil series. Mass of OC was measured for a surface layer, the A horizon and solum. The spatial dependence of OC mass was at a scale commensurate with topographic variation. Spatial analysis generally corroborated description of the sampling site by soil series. which represented differences in drainage as influenced by slope-position acid redistribution of water across the landscape. Soil series alone or grouped by drainage class, therefore, provided a framework by which to stratify the site for evaluation of effects of tillage practice on OC mass and extrapolation of results to comparable sites within the same landscape.