Stability of Soil Organic Carbon Pools Across a Rangeland Agricultural Management Gradient.

Soil organic carbon (SOC) is a reservoir for plant nutrients as well as a key component in soil aggregation, water holding capacity, and biogeochemical processes. Concerns about atmospheric CO₂ levels and global climate change have focused attention toward understanding SOC dynamics. Range management practices such as livestock grazing and vegetation manipulation likely influence the affinity of soils to sequester organic carbon. Our study investigated the stability of SOC pools (unprotected versus protected) across a gradient of rangeland agricultural management strategies. The gradient extends from non-grazed, non-thinned oak woodland through grazed and thinned annual grassland to irrigated and grazed perennial pasture. We also examined SOC stability across the various plant communities, which result from interactions between management, topographic, edaphic, and ecological factors. Such plant communities include: native perennial grass stands, annual grass and forb patches, annual weed patches, shrub patches, and blue oak/live oak/foothill pine complexes. Carbon stability was assessed by physically separating soils into coarse particulate organic matter plus sand (cPOM >250um), microaggregates (250-53 um), and silt plus clay (<53um) fractions. We then measured the hot water extractable and biochemically resistant sodium hypochlorite (NaOCl) extractable SOC on each of the physically separated soil fractions. We hypothesize that different management strategies will result in significantly different pools of protected and available organic carbon, which will be expressed in separate morphological soil horizons. Results of this study will be shared in this poster presentation.