Biodiversity, greenhouse gas and economic trade-offs from biochar use: a 20 year model of biochar use in the UK

Abstract:

Biochar is promoted for its carbon storage and soil amendment properties, but there remains a research gap into wider sustainability implications of biochar use. Without these there is a risk that biochar use could deliver negative unforeseen consequences. Key to biochar sustainability is the feedstock sustainability, which in developed nations can be novel due to the ability to process biomass locally.

Using field trial data and primary biodiversity assessments we modelled different sustainability indicators (local GHG balance, global GHG balance, local biodiversity, global biodiversity and local economic return) associated with four different biochar feedstocks (woodlands, hedgerows, Short Rotation Coppice (SRC) and straw) over 20 years for UK arable agriculture. Global measures included Indirect Land Use Change (ILUC).

Our results showed that trade-offs are inherent. Local GHG emissions are reduced by use of straw and SRC, and increased through the use of woodlands. In contrast all feedstocks reduced the global GHG emissions. Local biodiversity was increased through use of hedgerows, woodlands, SRC and low fertiliser rates. Global biodiversity was maximised through high fertiliser rates and use of all feedstocks. Critically economic return was maximised through high use of woodland and straw, and substantially reduced when hedgerows or SRC is used as feedstock. The introduction of high (£52 t^-1 CO₂) and low (£11.44 t^-1 CO₂) carbon prices were never enough to shift a system between loss and profit.

This research demonstrates that the sustainability of biochar varies substantially depending on the scale (local or global) and the breadth of indicators included. Ultimately biochar is designed to have a role in solving global problems, but the decisions determining use will be made locally. Regulation to ensure biochar is used appropriately may be necessary.