The Impact of Site Preparation for Biofuel and Sawtimber Production 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 large 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. The impacts of these non-traditional land management approaches on soil sustainability and productivity were evaluated. A first step in evaluating the conversion of monoculture plantations to a dual-crop system was to evaluate the potential impacts associated with land clearing for establishing switchgrass and the removal of coarse woody debris on the ‘without logging residuals’ treatments. Soil compaction measurements were obtained using a soil penetrometer to a depth of 30 cm at 2.5 cm intervals before and after treatment installation.  There were no significant differences in soil compaction before and after treatment installation. The average soil resistance across all treatments at the soil surface was 201 kPa and increased to 1539 kPa and 1923 kPa at 15cm and 30cm depths, respectively.  Clearing and site preparation treatments did not adversely affect soil tilth. The conversion of monoculture plantations into a dual-crop system consisting of switchgrass and loblolly pine is a feasible and sustainable practice at this time.