IMPACT OF SWITCHGRASS BIOENERGY FEEDSTOCK PRODUCTION ON SOIL CARBON DIOXIDE FLUX AND BELOW GROUND SOIL ORGANIC CARBON STORAGE IN EAST TENNESSEE

Bioenergy production from switchgrass has shown promise in restoring degraded soils and helping to mitigate greenhouse gas (GHG) emissions. CO2 loss and C-sequestration in soils are important topics for research to better understand the environmental impacts of bioenergy crops. The need for more thorough research of the carbon cycle in soils used for bioenergy production precipitated the primary interest of this study. The specific objectives of this study were 1) to measure SOC under switchgrass production in order to predict storage of carbon in soils based on previous cropping history, land management, soil physical characteristics, and time; and to 2) measure soil CO2 flux through the entire year to establish a) the annual, seasonal, and daily respiration rates, and b) use this data with soil carbon data to better understand the carbon life cycle in soils under switchgrass production in East Tennessee. Chapter 1 of the study was conducted on twelve farms across East Tennessee. Seven previous different cropping systems, four soil textural classes, and four soil taxonomy classes are represented in this study. There was an increase in SOC of roughly 1 Mg ha-1 from 2008 to 2011. No-till planting resulted in a significant increase in SOC compared to conventional tillage planting resulting in no significant changes in SOC. Chapter 2 results as hypothesized, soil temperature and moisture had a significant influence on CO2 flux variance. Soil temperature and soil moisture were able to explain 83% and 81.5% of variance in flux from clumps (cover) and between clumps (bare) respectively. The summer months exhibited the highest flux rate followed by spring, fall, and finally winter. Although largely overlooked in previous research, the winter months did contribute 5.4 MgCO2 ha-1 season-1 (±2.5 MgCO2 ha-1 season-1) from clumps (cover) and 4.0 MgCO2 ha-1 season-1 (±3.2 MgCO2 ha-1 season-1) from between clumps (bare). Annual switchgrass flux rate was 7.39 MgCO2 ha-1 (±4.08 MgCO2 ha-1)