Distributions of organic carbon and related parameters in a Louisiana sugarcane soil

• Spatial variability of soil organic matter (SOC) and nitrogen (N) were assessed.
• Semivariograms indicated extensive spatial structure for SOC and N.
• Cation Exchange (CDC) was well correlated with SOC for all sampled treatments.
• Influence of no-burn of sugarcane residue on soil carbon stock was inconclusive.

Soil organic carbon (SOC) is an important component of the global carbon budget. The aim of this study was to assess the spatial variability of SOC and nitrogen (N) in a long-term study of continuous sugarcane cropping in Louisiana. Soil core sampling along two transects of different residue management practices (1.8 m spacing and 1 m depth) was carried out; one where the residue was burned after harvest, and the other where the residue was left. The soil cores were sectioned in 10 cm increments and analyzed for SOC and N, pH, bulk density and cation exchange capacity (CEC). Significant correlations were observed between CEC and SOC. For individual soil depths, semivariogram analysis indicated that there was a lack of spatial variation for all properties measured. Semivariograms for the entire data set indicated extensive spatial structure for SOC, N and CEC. For the burned area, greatest spatial structure was observed for SOC and CEC. Vertical distribution results indicated that the no-burn area stored significantly more SOC and N than the burned. This finding was inconsistent with measurements made one year later (2013) where SOC and N results indicated no significant differences between the burn and no-burn areas. Results from a control area under bermudagrass indicated higher SOC and N near the soil surface compared to both the burn and no-burn. Based on two years of data, the influence of no-burn management of sugarcane residue on carbon stock in the soil profile is inconclusive.