Claims checked › Claim
Biochar boosts yields
“Adding biochar to the soil raises crop yields by 10 to 15%, or more.”
The 13% global average is real and it is a tropical number. Split by latitude, biochar raised yields 25% on acid, poor tropical soils and lowered them 3% in temperate regions. European field trials on fertile and calcareous soils find nothing.
Where it comes from
Meta-analyses that report a grand mean of roughly 10 to 15%, quoted without their split, and producers, certifiers and consultancies who quote the grand mean.
Who benefits
Biochar producers, the private certificate body, carbon-credit registries and the consultancies around them. The market grew from $14.6 million in 2022 to $181.5 million in 2024 (CDR.fyi); a yield story helps sell the product to the farmer who spreads it.
What the evidence says
The average hides two opposite results. Jeffery and colleagues pooled 1,125 paired comparisons from 106 papers (2017, Environmental Research Letters). Grand mean +13%. Tropics +25% (527 comparisons). Temperate regions −3%, a small but significant decrease across 598 comparisons from 44 papers. The gain "was highest for soils with lowest pH prior to biochar application and the effect systematically declined as initial soil pH increased"; biochar's benefit is a nutrient and liming effect on poor acid soils, and on fertile, fertilised temperate soils "adding more nutrients is unlikely to have any impact" (open access).
European trials agree. Seven biochars applied for three years to processing tomato on two fertile Mediterranean-climate soils produced "no impact on crop yield" (Field Crops Research, 2025, as reported). Low-rate biochar in a highly alkaline dryland Calcisol had no significant effect on wheat (as reported). The UK's 2010s field programme found small, site-specific outcomes (Carbon Management, 2013).
The exceptions are irrigated perennials or extreme rates. An irrigated super-intensive olive grove gave 18% more olives per tree; durum wheat gained up to 30% at 30 and 60 t/ha, which at €400 to €600 a tonne is €12,000 to €36,000 a hectare.
What to say instead
"Biochar raises yields on acid, poor soils, mostly in the tropics. In temperate and calcareous Europe it does not, and it costs €4,000 to €18,000 a hectare at the rates the trials use." The biochar page grades yield, water and carbon separately.