The Role of Organic Matter in Rangeland Sustainability

ABSTRACT THE ROLE OF ORGANIC MATTER IN RANGELAND SUSTAINABILITY by Cori Hutchens Master of Science in Environmental Science: Professional Science Master Option California State University, Chico Spring 2011 Gaining a mechanistic understanding of soil organic carbon (SOC) controls may help land managers retain soil health and possibly sequester CO2. The present study examined the level of SOC and soil moisture (SM) on five pastures of varying grazing intensities (0.52, 0.61, 0.66 AU/Ha) in a northern California rangeland. Three one year old cattle exclosures in each pasture were also sampled. Samples were taken at depths of 2-20 cm and 20-30 cm. Vegetation present at each site was identified and categorized as predominantly native, non-native, or an even mix of both. The overall loss of SOC over the dry season as well as the strong positive correlation between SM and TOC (P.0001) indicated that environmental variables, especially precipitation and temperature, play a significant role in SOC concentrations. Sites that were categorized as native tended to have more SM and SOC than non-native sites. The interaction between plant type and SM and SOC increased with depth and decreased during the dry season. With the large extent of rangelands in the U.S. and around the world, small changes in SOC concentrations on rangelands may have large impacts on the global carbon budget. Moreover, compared with geologic or geo-engineered sequestration methods, that may be unproven or not currently cost effective, increasing SOC provides ecosystem benefits such as improved water holding capacity, soil structure, nutrient cycling, and a decreased risk of erosion.