Bioenergy Production On Intensively Managed Loblolly Pine Plantations Alters Soil Chemical and Physical Properties.

Concern over rising atmospheric CO₂ due to fossil fuel combustion and its impact on climate has intensified research into carbon-neutral energy and fuel production.  Pine-switchgrass agroforestry ecosystems are a viable option to reduce atmospheric CO₂ by potentially offsetting fossil fuel consumption and increasing SOC.  Our objective is to study effects of loblolly pine-switchgrass intercropping systems on ecosystem resource use efficiency and biogeochemical cycling of C and nutrients.  In summer 2008, four blocks of seven plots (0.8 ha treatment plots with 0.4 ha measurement plots with a minimum 15 m outer buffer) were established on a recently harvested 25-year-old loblolly pine plantation near Dover, NC.  Treatments included: 1) traditional pine establishment with residuals left in place; 2) traditional pine establishment with residuals removed; 3) pine intercropped with switchgrass between bed rows with residuals left in place; 4) pine intercropped with switchgrass between bed rows with residuals removed; 5) pine establishment with “extra” row of trees flat‐planted in between crop tree beds with residuals left in place; 6) pine establishment with “extra” row of trees flat‐planted in between crop tree beds with residuals removed; and 7) switchgrass only.  Here we present one year of data on exchangeable anions and cations in the top 10 cm of mineral soil in established treatment plots.  Membranes were analyzed for N, P, Ca, Al, Fe, Mg, Mn, B, Cu, and Zn.  Temporal patterns of inorganic nutrients and other elements indicate that various treatments have altered the biogeochemical cycling of these elements.  Different rooting and canopy zones occupied by pine and switchgrass and variation between these species main physiological periods during the growing season may alter the biogeochemical cycling of nutrients.