Belowground Competitive Interactions within Pine-Switchgrass Co-Culture.

Establishing co-production systems of bioenergy feedstocks and high-value sawtimber crops could provide landowners with management options to increase net productivity and diversify income earning potential. However, tradeoffs in productivity due to interspecific competition could affect resource availability within these systems. The objective of this study is to quantify belowground competition for soil water and available nitrogen in loblolly pine-switchgrass co-culture. Two co-culture production sites were established in 2011 on the upper Gulf Coastal Plain. Treatments included switchgrass only and pine only, as well as pine planted into switchgrass with 0-foot, 2-foot, and 4-foot competition free zones on either side of the row of pines. Soil moisture and nutrient cores were collected over the 2011 growing season at three distances in proximity to tree rows: 0 ft (within tree row), 2 ft on either side of the pines, and 4 ft on either side of the pines. Additional measurements will be collected throughout the 2012 growing season. We will present preliminary indications of soil resource availability in co-culture across varying levels of competitive intensity.