Enhanced rock weathering in grassland: Impacts of basalt dust on hay meadow soil, forage, and floristic diversity.

Enhanced rock weathering (ERW) is a promising carbon dioxide removal (CDR) technique with agricultural co-benefits, though its efficacy in grasslands remains largely unexplored. Permanent grasslands, such as hay meadows, can support high floristic diversity, but their agronomic and biodiversity responses to surface-applied silicate rock dusts are unknown. To address this, 50 t ha-1 basalt rock dust was spread on a floristically rich (>28 vascular plant species, ∼ 25 m-2), mildly acidic (pH = 6.35) upland hay meadow in the UK, and its effects on soil chemistry and plant diversity were studied. In the first season, basalt-treated plots showed significantly higher concentrations of Ca, Mg, Na, and Si than controls, although no clear temporal accumulation trend was observed. After 1 year, basalt increased soil pH at 0-10 cm by 0.25 units and raised concentrations of exchangeable calcium (+13%), magnesium (+14%), sodium (+22%), and silicon (+35%). This suggests a potential maximum CDR of approximately 542 kg CO2 ha-1 yr-1 in the upper 10 cm of soil, before considering cation sorption and strong acid effects. The trace elements barium, cadmium, caesium, cobalt, nickel, chromium, strontium, and vanadium increased in the soil, but only strontium significantly increased in plant shoots, and no elements reached ecotoxic levels. Magnesium, sodium, and phosphorus concentrations also increased in plant shoots and hay, while no changes occurred in forage yield, sugar, protein, or digestibility. Importantly, basalt amendment did not significantly impact Simpson or Shannon-Wiener plant diversity indexes. These findings suggest that even the short-term application of basalt to floristically diverse UK grasslands may provide CDR while benefiting plant and soil nutrition, without compromising floristic diversity or forage quality.