Short-Term Stability of Soil Organic Carbon in Biofuel Cropping Systems Established on Contrasting Soil Textures.

Conversion of conventional row crop agriculture to biofuel cropping systems such as no-till corn, perennial grasses, or short-rotation woody crops may sequester atmospheric CO₂ in soil organic carbon (SOC) through increased plant inputs to soil and decreased soil disturbance. SOC is not a homogenous substrate, but rather is composed of a heterogeneous continuum of organic materials ranging from very labile, easily decomposable plant litter inputs to more stable, persistent forms. The process of stabilization occurs when plant inputs are physically incorporated into soil aggregate structures or chemically protected from decomposition through adsorption onto mineral particles. Our objective was to examine the effect of biofuel cropping systems (plants and management) and soil texture on SOC stability in order to evaluate the potential for such systems to act as long-term SOC sinks. We collected soils following 5 years of biofuel cropping system establishment on contrasting soil types from Arlington, WI (ARL) and Kellogg Biological Station, MI (KBS). We used a density fractionation method to isolate a free light fraction (FLF), occluded light fraction (OLF), and heavy fraction (HF), which represent physically unprotected, aggregate protected, and mineral protected SOC pools, respectively. We found a greater proportion of the total soil mass within the unprotected FLF in the coarse-textured soils at KBS compared to the fine-textured soils at ARL. In contrast, a greater percentage of the total soil mass was located in the aggregate-protected OLF at ARL than at KBS. Twice as much SOC was associated with the HF at ARL compared to KBS, highlighting the importance of soil texture in controlling mineral protection of SOC. Overall, a larger proportion of total C was protected from decomposition in the fine-textured soil suggesting that soil texture plays a key role in SOC stability in biofuel cropping systems.