Agronomic co-benefits of enhanced rock weathering in smallholder farming systems of central India

Enhanced rock weathering (ERW) using silicate rock amendments represents a promising carbon dioxide removal (CDR) strategy, yet its viability in smallholder agriculture hinges on demonstrable agronomic co-benefits. Here we report findings from a farmer-participatory field trial conducted across smallholder cropping systems in central India, designed to quantify productivity responses and changes in input requirements following basalt application.

Basalt rock powder (particle size <2 mm) was applied at a mean application rate of 25 metric tons ha⁻¹. The study included 42 smallholder farmers  managing over 200 ha of agricultural land. All plots were monitored over a full annual cycle encompassing multiple cropping seasons (Kharif and Rabi). Yield, fertiliser application rates, crop health indicators, irrigation frequency, and farmer-reported observations were recorded. Treatment effects were assessed as within-plot changes relative to farmers' baseline practices from the previous year under identical crop rotations.

Basalt-amended farms showed significantly higher crop yield relative to baseline and compared to controls (mean difference: 9%, p < 0.05). Yield gains exceeding 5% were observed in 70% of the treatment plots, with 45% showing increases > 10%. Fertiliser application rates showed a decreasing trend in 82% of basalt-treated plots, with 60% reporting reductions of ≥10%; absolute fertiliser inputs were lower in treatment plots compared to control plots. Improved crop health was reported by 63% of participating farmers, while 29% noted reduced irrigation requirements. Farmer acceptance was high, with 60.5% indicating willingness to recommend ERW adoption within their communities.

These field-scale observations suggest that ERW deployment in smallholder systems can yield agronomic benefits, alongside carbon sequestration, potentially facilitating adoption through reduced input costs and enhanced productivity, rather than relying solely on carbon finance.

Keywords: Enhanced Rock Weathering, Carbon dioxide removal, Smallholder agriculture, agronomic co-benefits.