Role of clay minerals on soil organic matter stabilization and humification

An understanding of organic C dynamics in soils is necessary to develop management options to enhance soil organic C sequestration. The objective of this research was to study the distribution of newly formed humic materials into mineralogical distinct clay-size fractions of a silt loam soil. Oats (Avena sativa L), grown under simulated no-tillage conditions, were pulse labeled with CO2. After senescence, the surface residue was removed and the labeled roots were allowed to decompose in the soil for 360 days. The soil clay fraction (<2 ym) was separated into coarse, medium, and fine clay size-fractions (0.2-2.0, 0.02-0.2 and <0.02 iim, respectively) by centrifugation. X-ray diffraction indicated that quartz, illite, and kaolinite were the dominant mineral phases in the coarse clay fraction while smectite was the dominant mineral phase in the fine clay fraction. The organic C content in the coarse and fine clay fractions (3.70 and 3.93%, respectively) were similar. Scintillation analysis indicated an increase in 14C specific activity in all