Application of basalt reduces nitrous oxide evolution from annual and perennial crops

Agricultural lands in the American Midwest are a major source of nitrogen, both to the atmosphere and to the water cycle, due to overuse of nitrogen fertilizers in intensive maize production. The application of metamorphose basalt to Illinois cropland to reduce atmospheric CO₂ through "enhanced weathering," the process of supplying cations to sequester CO₂ as bicarbonate, resulted in reduced N₂O production from soil in annual and perennial crops. Pulverized basalt (5 kg m^-2) was tilled into conventionally-managed maize fields and surface-applied to perennial Miscanthus x giganteus. Soil was sampled at monthly intervals for pH, which increased more rapidly in basalt-treated plots and remained higher than control plots at the end of the growing season. N₂O was sampled using respiration collars with PVC chambers in 30-minute incubations and analyzed by gas chromatograph. In heavily-fertilized annual maize, where basalt was tilled under, annual N₂O production was reduced from 7.1 to 5.7 kg ha^-1 y^-1 in basalt-treated blocks, a statistically significant difference of 19%. In M x giganteus, where overall N₂O production was 1/10^th of annual maize, basalt-treated plots produced 46% less N₂O over the course of the growing season, 0.59 kg ha^-1 y^-1 in controls and 0.32 kg ha^-1 y^-1 in basalt plots. While enhanced weathering with basalt was intended to mitigate greenhouse gases by sequestering CO₂, the effect on soil pH and N₂O release from cultivated soils, which can account for up to 40-60% of annual N₂O lost to the atmosphere globally, may be more critical in the short term, as N₂O is a more potent greenhouse gas than CO₂. Additionally, reduced N loss to the atmosphere may be a sign of improved nitrogen use efficiency, confirmation of which could change the application rate of N fertilizer and tighten the N cycle in agricultural ecosystems.