Effects of High-Density, Short-Duration Planned Livestock Grazing On Soil Carbon Sequestration Potentials in a Coastal California Mixed Grassland.

Planned grazing management in rangelands may improve carbon sequestration potential of soils by increasing plant biomass and the rate of nutrient cycling, which might mitigate global warming. The effects of high-intensity, short-duration planned grazing on several soil quality indicators and ecosystem properties will be investigated on a mixed grassland in San Luis Obispo, CA. Short-duration grazing by sheep at high densities of up to 110,000 pounds per acre is applied at two sites with clay-loam soils: a rangeland site that has been rested for 40 years, and an adjacent site that has been grazed for six years. The objectives of this study are to determine if planned grazing will improve soil carbon sequestration, and quantify changes in identified variables in grazed and rested plots. Soil organic carbon, total nitrogen, labile and recalcitrant carbon, bulk density, soil structure and color, plant species composition and percent vegetative cover will be monitored over the course of two years. Baseline data analysis shows a significantly higher percentage of soil organic carbon at the grazed site, with an average of 0.60% more soil organic carbon at a depth of 0-3 cm when compared with the rested site. There is no difference in total nitrogen between the two sites. Soil pH is significantly lower at the grazed site by an average of 0.63 at a depth of 0 to 3 cm, and 0.81 at a depth of 3 to 6 cm. It is hypothesized that planned grazing will improve soil physical, chemical, and biological indicators and increase the amount of carbon sequestered in the soil. As rangelands cover 50% of the world’s terrestrial surface, a 1% increase in soil organic matter could result in sequestration of more than all of the world’s excess atmospheric carbon. If grazing can be used in California as a strategy for increasing soil carbon sequestration, the rates of desertification may be slowed and damage caused to the ecosystem by global warming may be reduced.