Table 2 Model parameters and output of scenarios for mineral-enriched biomass pyrolysis and subsequent biochar soil application.

Scenario	Biomass	Mineral addition		Reference scenario	Biomass costs	Mineral costs	Stable carbon yield	CO₂ removal costs
		Types	Amounts		(US$ t⁻¹)	(US$ t⁻¹)	References	US$ t⁻¹	% of reference
Baseline (a)	Miscanthus	–	–	–	87⁹⁶	–	¹⁶	202	–
Baseline (b)	Woody residues	–	–	–	50⁹⁶	–	²⁵	140	–
Baseline (c)	Rice straw	–	–	–	59⁹⁶	–	⁸⁷	149	–
a	Miscanthus	Potassium acetate	1%, 2%	Baseline (a)	87⁹⁶	1000⁹⁷	¹⁶	185, 168	−8, −17
b	Woody residues	Wood ash	5%, 10%, 20, 50%	Baseline (b)	50⁹⁶	0	²⁵	125, 121, 119, 150	−11, −14, −16, +6
c	Rice straw	Vermiculite	20%	Baseline (c)	59⁹⁶	140⁷⁴	⁸⁷	131	−12
Baselines (d)	Miscanthus	–	–	–	0–200	–	¹⁶	388	–
Baselines (e)	Woody residues	–	–	–	0–200	–	²⁵	403	–
Baselines (f)	Rice straw	–	–	–	0–200	–	⁸⁷	376	–
d	Miscanthus	Potassium acetate	1%, 2%	Baselines (d)	0–200	750–1250	¹⁶	342, 301	−12, −22
e	Woody residues	Wood ash	5%, 10%, 20, 50%	Baselines (e)	0–200	0	²⁵	349, 329, 310, 326	−13, −18, −23, −19
f	Rice straw	Vermiculite	20%	Baselines (f)	0–200	105–175	⁸⁷	269	−28

Simulation of biomass enrichment with (a, d) a refined, soluble mineral (potassium acetate) to bioenergy crop biomass (miscanthus), (b, e) mineral residues (wood ash) to forestry residues (woody residues) and (c, f) ground rocks (vermiculite) to agricultural residues (rice straw). For scenarios (d), (e) and (f), a range of biomass feedstock and mineral costs were modelled and the CO₂ removal costs are given for the highest biomass costs (US$ 200 t⁻¹) and medium mineral cost scenarios. Full results are displayed in Fig. 4. Details about modelling of CO₂ removal costs can be found in the Supplementary Methods.

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