Soil greenhouse gas emissions and soil C dynamics in bioenergy crops

Second generation bioenergy crops short rotation coppice (SRC) willow and Miscanthus x giganteus are the two main bioenergy crops grown in the UK. The first aim of this research was to quantify the in situ soil greenhouse gas (GHG) budget and to establish the drivers of these GHG fluxes for SRC willow and Miscanthus. The second aim of this research was to provide a more in-depth understanding of C cycling under Miscanthus i.e. litter and roots through two field experiments. The main findings were: The results from this work confirmed minimal emissions of CH4 and N2O from soil in second generation crops (non-food crops), SRC willow and Miscanthus. CO2 flux was found to be the major efflux from soils in both crops and showed a positive correlation with temperature and showed a negative correlation with soil moisture content. The majority of total CO2 flux from the soil surface under Miscanthus was from underground processes, with little contribution from aboveground litter decomposition to total flux. Litter played an important part in providing nutrients to the soil, which is vital in these crops since they are not fertilised. The high C:N ratio of Miscanthus litter and the high lignin content of SRC willow, resulted in an accumulation of litter on the soil surface and so may promote long-term C sequestration. Overall, the results from this work, combined with other literature would suggest that these crops offer advantages to first generation crops but more field-based studies are required to be able to say if these crops can offer large-scale GHG savings needed from this renewable energy source