Switchgrass-Pine Agroforestry Systems: Soil Carbon and Biomass Production.

Global climate change is the most challenging environmental issue of this century. Soil carbon sequestration and replacement of fossil fuel dependence with bioenergy crops, have been  identified as two major strategies of climate change mitigation. This project involves the intercropping of switchgrass (Panicum virgatum) into a silviculture stand of longleaf pines (Pinus palustris). Switchgrass is an energy grass that has high yield in biomass under low nutritional and management requirements.  The switchgrass was established, harvested, and analyzed within one year. This C4 grass was grown based on the sub-treatments of three fertilizer applications amongst four treatments of long leaf pines (C3) at different ages per stand of trees. The three fertilizers applications were no fertilizer, organic, and inorganic. These applications were conducted in a random fashion four times within varying age classes (stands):  no pines, first-year seedlings, 3-5 year old pines, and 6-8 year old pines.  Soil samples were taken prior to and after the first year establishment of switchgrass in a proximity to the base of the plants, and was followed by harvesting the switchgrass.  The objectives were to compare the growth, survival and biomass production of switchgrass under different pine age-class treatments and fertilizer sub-treatments.  The switchgrass was collected from the field sites and dried upon removal for dried biomass analysis. Then the total organic carbon either sequestered or released by the practice had been analyzed through sample comparisons taken prior to and after the growing season.  Estimates have been made about the individual soil organic carbon contributions from switchgrass (C4 plant) and pine (C3 plants) through isotopic analysis of the soil samples. Soil carbon and biomass analyses were done at GSU’s Agroecology lab and the isotopic analysis was done at the Skidaway Island Institute.