Biochar and certification 1
Soil organic carbon (SOC) sequestration is considered by the Intergovernmental Panel on Climate Change as a negative emissions technology. Biochar offers increased SOC sequestration potential under some scenarios and is often praised for addressing multiple agronomic and environmental challenges simultaneously, although trade-offs between such benefits are inevitable. A workable sustainable biochar certification system, based on extended sustainability criteria, is essential to minimise trade-offs and avoid potential negative side-effects, both for the environment and the biochar production industry. Two nascent biochar certification programmes and standards exist today: (i) the International Biochar Initiative (IBI) Biochar Certification Program; and (ii) the European Biochar Certificate. Both certification schemes aim to optimise the biochar production and commercialisation sector, promoting quality and safety guidelines. It is a prerequisite that biochars have to fulfil a set of basic quality specifications (e.g. C content, porosity, pH, contents of metals and polycyclic hydrocarbons contents). Biochar can remain in soils for decades to millennia, and is practically irreversible once applied. Since some of the criteria and benchmarks are drawn from composting legislation, which may not be fully applicable to biochar, such standardisation and certification schemes need further development.
Between different biochar–soil–crop–climate combinations there are varying dose responses for each soil-based ecosystem service (ES). For example, evidence suggests that increased biochar doses (up to 50tha–1) generally leads to increased crop productivity in tropical regions, but with limited significant yield effects in temperate regions. The Optimum Biochar Dose (OBD) concept addresses the optimal ES’s trade-off, by determining the biochar application rate at which various ecosystem services respond in relation to their overall desired response. The relatively long residence time of biochar remains a challenge for ES modelling frameworks for land management and policy. A number of possible trade-offs are addressed in current certification schemes, namely associated with biodiversity outcomes, directly or indirectly. These include criteria such as resource management or threshold contents of trace elements and organic compounds in biochar. Further contextualisation of such criteria and their possible extension to include the OBD concept and effect-based approaches is provided. There is also another side to this coin. Biochar can also have positive biodiversity outcomes, and thus, potentially contribute to sustainable management, preservation and/or function recovery in vulnerable or degraded ecosystems. Exploring such targeted applications with regard to sustainable (agro)ecosystem management will require comprehensive consideration of biodiversity outcomes.