Basalt Application Alters the Nitrogen Budget of Midwestern U.S. Agricultural Soils through Reduced Nitrous Oxide Fluxes and Increased Nitrogen Leaching

Land-based enhanced rock weathering (ERW)─applying ground silicate rock to soils─is being explored for sequestration of CO2 from the atmosphere, with impacts beyond carbon storage. Weathering of basalt releases base cations increasing alkalinity and soil pH, which we hypothesized would reduce N2O emissions. Repeated applications of basalt to a heavily fertilized annual Zea mays and Glycine max rotation (maize and soybean) and the low-fertilized perennial bioenergy grass Miscanthus x giganteus (miscanthus) in Illinois raised soil pH from 6.6 to 7.1 in maize/soybean and from 5.4 to 6.3 in miscanthus and consistently reduced annual N2O emissions by 16–40% over 7 growing seasons. Although not statistically significant for any given crop, our results indicate an emerging trend of increased N leaching (23% pooled across crops and years), suggesting a potential shift in N loss from the atmosphere to groundwater. Crop yields increased or remained unchanged, indicating enhanced weathering is compatible with conventional farming practices. Regional land model simulations show that ERW deployment across the US Corn Belt could reduce soil N2O emissions by 11% under a moderate deployment pathway and by 24% under a more intensive deployment pathway. The effects of enhanced weathering extend beyond CO2 sequestration and may benefit both greenhouse gas mitigation and bioenergy crop production, with a potential trade-off of increased N mobility in fertile, organic matter-rich US Midwestern soils.