Operationalising net-zero with biochar: black gold or red herring?

<p>Nascent anecdotal evidence implies that livestock feed supplementation with biochar may reduce enteric methane, improve liveweight gains and improve soil carbon through enrichment of manure. Here we dissect this hypothesis using a transdisciplinary participatory approach. We show that steers fed biochar ad libitum increased liveweight gain relative to non-supplemented controls (5% improvement after 14 months). At carbon prices of $25-75 Mg-1 CO 2-e and biochar costs of $2,000 Mg-1 , liveweight gains would need to be at least 5% greater than non-supplemented controls to be profitable. Profit per animal was more sensitive to liveweight gains compared with enteric methane mitigation, suggesting greater economic value in pursuing types of biochar that elicit a productivity co-benefit, rather than biochar for mitigation of enteric methane. Our modelling of industry adoption showed that peak adoption of biochar was 10-69% over 5-7 years, depending on perceived environmental benefits and ease of trialing. Through participatory discussions with farmers, we revealed multiple strengths (e.g. animal health co-benefits and recalcitrant properties of biochar in the soil), weaknesses (cost, knowledge requirements), opportunities (carbon markets, use in feedlots) and threats (potential antagonism with other feed additives, regulation) associated with biochar feed supplementation. We contend that livestock feed supplementation with biochar comprises a prospective pillar towards reducing agri-food GHG emissions in a sustainable way, and we recommend further research in this endeavor.</p>