The Impact of Annual Harvesting of Switchgrass Intercropped In Loblolly Pine Plantations On Soil Compaction and Long-Term Soil Productivity.

As efforts rise to mitigate CO₂ emissions associated with increasing global demand and consequently burning of fossil fuels, research into renewable fuels has increased. Utilizing forest biomass for biofuel production has emerged as a promising approach. However, very little research has focused on how to simultaneously grow biomass for biofuel production while still managing for high quality wood products.  Furthermore, the potential effect that this could have on long-term soil productivity is critical for the viability of such an intensive management system.  As a result of this gap in scientific knowledge, a long term study has been established on the lower coastal plain of North Carolina that investigates the effects of intercropping and biomass management on site productivity and sustainability. The study consists of the following treatments with and without logging residuals: 1) pure loblolly pine (Pinus taeda L.) plantation, 2) loblolly pine with switchgrass (Panicum virgatum L.) between beds, and 3) loblolly pine establishment with flat-planted pine trees between crop tree beds. Pure stands of switchgrass were also established.  All seven treatments were established on 0.81 hectare plots and were replicated four times.  The site preparation for each treatment varied in intensity and number of entries with heavy equipment. Furthermore, treatments with switchgrass also require annual entries to cut, rake, and bale this feedstock.  The impacts of these non-traditional land management approaches on soil sustainability and productivity were evaluated. Soil compaction measurements were obtained using a soil penetrometer to a depth of 30 cm at 2.5 cm intervals at four different time periods: 1) before and 2) after treatment installation, 3) following a cut only treatment at the end of year one, and 4) at end of year two which included cutting, raking and baling of material.  Intensively managing and removing switchgrass on an annual basis in intensively managed pine plantations has no significant effect soil compaction following two growing seasons.  This suggests that this non-traditional management for both biofuel and sawtimber production is a feasible and sustainable practice at this time.