Assessment of Soil Organic Carbon and Total Nitrogen Stocks Under Conservation Management Practices in a Claypan Agroecosystem Using An Adapted ANOVA.

Soil organic carbon (SOC) and total nitrogen (TN) play crucial roles in the global carbon cycle and agricultural practices can dramatically impact stocks of SOC and TN. Conservation management practices have the potential to enhance carbon sequestration and improve profitability and sustainability. This study used a modified two-factor analysis of variance (ANOVA) with subsamples to compare SOC and TN concentrations and volumetric stocks in a claypan agroecosystem under no-till management ten years after grass and agroforestry vegetative filter strips (VFS) were installed. The effects of three vegetative covers (no-till, grass VFS and agroforestry VFS) and four landscape positions (summit, shoulder, backslope and footslope) were evaluated at the 0-5 cm and 5-13 cm depth. In the surface layer, the mean SOC concentration was significantly greater in both VFS soils compared to no-till while the mean TN concentration was significantly greater only in the grass VFS relative to no-till. When SOC and TN stocks were calculated on a volumetric basis utilizing soil bulk density, no significant differences were found among treatments in this layer. A rapid slaking stability test used to separate physically occluded SOC and TN found significantly higher mean occluded SOC and TN concentrations and volumetric stocks in VFS soils than under no-till. In addition, the occluded SOC:TN ratio was significantly different from the total SOC:TN ratio, suggesting greater stabilization and reduced decomposition of SOC in the occluded fraction. The results of this study indicate that although mean SOC and TN concentrations may differ between no-till and VFS soils after ten years, there is insufficient evidence to conclude that mean SOC and TN stocks are significantly different among these vegetative covers. Treatment effects of vegetative cover in the occluded fraction, however, suggest a higher proportion of SOC and TN are physically stabilized in the VFS soils relative to no-till.