Fig. 2: Annual net CO₂ emissions from maize-derived biomethane relative to a natural gas counterfactual, expressed per unit area of crop production, relative to the soil-derived CO₂ emissions from that land area.

The central black line is based on average biomethane yields per hectare of UK maize, while the upper and lower grey lines show the impact of an (arbitrary) 50% lower or higher biomethane yield, respectively. The dashed blue line shows the break-even point beyond which soil CO₂ emissions exceed the avoided emissions from substitution of natural gas. The solid yellow line shows the level of soil CO₂ emissions and net biogas emissions, resulting from bioenergy crop cultivation on drained thin peaty soils (UK Tier 2 EF); solid red and dashed black lines show the equivalent figures for thicker peat soils based on the UK Tier 2 EF and IPCC Tier 1 EF for temperate cropland on peat, respectively.