Land‐based enhanced rock weathering (ERW) is a biogeochemical carbon dioxide removal (CDR) strategy aiming to accelerate natural geological processes of carbon sequestration through application of crushed silicate rocks, such as basalt, to croplands and forested landscapes. However, the efficacy of the approach when undertaken with basalt, and its potential co‐benefits for agriculture, require experimental and field evaluation. Here we report that amending a UK clay‐loam agricultural soil with a high loading (10 kg/m²) of relatively coarse‐grained crushed basalt significantly increased the yield (21 ± 9.4%, SE) of the important C₄ cereal Sorghum bicolor under controlled environmental conditions, without accumulation of potentially toxic trace elements in the seeds. Yield increases resulted from the basalt treatment after 120 days without P‐ and K‐fertilizer addition. Shoot silicon concentrations also increased significantly (26 ± 5.4%, SE), with potential benefits for crop resistance to biotic and abiotic stress. Elemental budgets indicate substantial release of base cations important for inorganic carbon removal and their accumulation mainly in the soil exchangeable pools. Geochemical reactive transport modelling, constrained by elemental budgets, indicated CO₂ sequestration rates of 2–4 t CO₂/ha, 1–5 years after a single application of basaltic rock dust, including via newly formed soil carbonate minerals whose long‐term fate requires assessment through field trials. This represents an approximately fourfold increase in carbon capture compared to control plant–soil systems without basalt. Our results build support for ERW deployment as a CDR technique compatible with spreading basalt powder on acidic loamy soils common across millions of hectares of western European and North American agriculture.

• Large proportions of the Earth’s land surface are covered by biomes dominated by C₄ grasses. These C₄-dominated biomes originated during the late Miocene, 3–8 million years ago (Ma), but there is evidence that C₄ grasses evolved some 20 Ma earlier during the early Miocene/Oligocene. Explanations for this lag between evolution and expansion invoke changes in atmospheric CO₂, seasonality of climate and fire. However, there is still no consensus about which of these factors triggered C₄ grassland expansion. • We use a vegetation model, the adaptive dynamic global vegetation model (aDGVM), to test how CO₂, temperature, precipitation, fire and the tolerance of vegetation to fire influence C₄ grassland expansion. Simulations are forced with late Miocene climates generated with the Hadley Centre coupled ocean–atmosphere–vegetation general circulation model. • We show that physiological differences between the C₃ and C₄ photosynthetic pathways cannot explain C₄ grass invasion into forests, but that fire is a crucial driver. Fire-promoting plant traits serve to expand the climate space in which C₄-dominated biomes can persist. • We propose that three mechanisms were involved in C₄ expansion: the physiological advantage of C₄ grasses under low atmospheric CO₂ allowed them to invade C₃ grasslands; fire allowed grasses to invade forests; and the evolution of fire-resistant savanna trees expanded the climate space that savannas can invade.

Meeting internationally agreed-upon climate targets requires carbon dioxide removal (CDR) strategies coupled with an urgent phase-down of fossil fuel emissions. However, the efficacy and wider impacts of CDR are poorly understood. Enhanced rock weathering (ERW) is a land-based CDR strategy requiring large-scale field trials. Here we show that a low 3.44 t ha⁻¹ wollastonite treatment in an 11.8 ha acid-rain-impacted forested watershed in New Hampshire, USA, led to cumulative carbon capture by carbonic acid weathering of 0.025–0.13 t CO₂ ha⁻¹ over 15 years. Despite a 0.8–2.4 t CO₂ ha⁻¹ logistical carbon penalty from mining, grinding, transportation, and spreading, by 2015 weathering together with increased forest productivity led to net CDR of 8.5–11.5 t CO₂ ha⁻¹. Our results demonstrate that ERW may be an effective, scalable CDR strategy for acid-impacted forests but at large scales requires sustainable sources of silicate rock dust.