Management practice effects on spatial variability characteristics of surface mineralizable C

Information on spatial variability of different C pools and fractions is important for site-specific monitoring the changes in soil carbon (C) on a farm-scale basis. The objectives of this study were to compare the effects of 16 years of implementation of conventional chisel-plowed management practice (CT) and organic cover crop based practice (CT-cover) on spatial variability of C mineralized in a 210-day incubation; and to study the effects of topography, texture, plant biomass input, and total soil C on mineralizable C. For each management practice we collected more than 350 soil samples at 0–5 cm depth in well-drained Typic Hapludalfs in southwest Michigan. The spatial continuity of CO2 respired C was found to be relatively weak with the variability at distances < 1 m constituting more than 65% of the overall variability. In either treatment, only a small portion of variability in CO2 respired C (11–16%) was explained by multiple regression models with topography (WI), soil texture (clay + silt content), main crop biomass, and total C. There was a positive direct effect of total C and a negative direct effect of clay + silt on CO2 respired C. The practical implication of these findings for modeling soil C processes on a farm scale is that in soils similar to those of this study producing site specific maps of labile C inputs using either spatial auto-correlation or auxiliary variables will likely not be feasible.