An estimate of the technical potential for land-based carbon sequestration using the perennial biomass crop Miscanthus x giganteus – A case study in Wales, UK

Concern around anthropogenic climate change is increasingly focussing attention on the impacts of agricultural greenhouse gas emissions, and the potential for the sector to offset these with carbon farming for biomass. Where existing farming systems offer low returns and limited enterprise options, such as less favoured farming areas (LFA) across Europe, options to diversify enterprises and access alternative markets are scarce and sorely needed. Here we consider Wales, a nation within the United Kingdom with predominantly LFA grassland agriculture. The UK climate advisory body recommended 56 kha of Welsh agricultural land should be moved to biomass cropping by 2050 to contribute to emission targets. We investigated the technical potential for carbon sequestration using Miscanthus x giganteus, assuming the entire 56 kha to be planted in a single year (2025), and modelled biomass production, harvest offtake and soil carbon changes by 2050. We used GIS mapping to estimate the maximum suitable planting area, and spatially explicit crop-growth model predictions to compare yield-optimised planting locations with random distribution. Our soil carbon decomposition model, driven by predicted crop litter production, estimated changes in SOC over the cropping period. Finally, we considered potential impacts on existing land-use in terms of reduced grazing capacity. Results showed that optimising distribution of the crop naturally favoured sites with lower baseline soil carbon stocks and greater sequestration rates. SOC increased by 0.39 Mt. SOC by 2050 under optimised distribution, compared to 0.03 Mt. SOC distributed randomly. Cumulative harvest offtake by 2050 for the 56 kha was between 9.06 and 10.26 Mt. C dependant on distribution strategy. Finally, we showed that the reduction in grazing capacity represented by a 56 kha move to biomass production from 2025 to 2050 would be 10 to 40 times less than the increase in capacity that happened over the previous 25 years.