In silico assessment of the potential of basalt amendments to reduce N₂O emissions from bioenergy crops

The potential of large-scale deployment of basalt to reduce N₂O emissions from cultivated soils may contribute to climate stabilization beyond the CO₂-removal effect from enhanced weathering. We used 3 years of field observations from maize (Zea mays) and miscanthus (Miscanthus × giganteus) to improve the nitrogen (N) module of the DayCent model and evaluate the potential of basalt amendments to reduce N losses and increase yields from two bioenergy crops. We found 20%–60% improvement in our N₂O flux estimates over previous model descriptions. Model results predict that the application of basalt would reduce N₂O emissions by 16% in maize and 9% in miscanthus. Lower N₂O emissions responded to increases in the N₂:N₂O ratio of denitrification with basalt-induced increases in soil pH, with minor contributions from the impact of P additions (a minor component of some basalts) on N immobilization. The larger reduction of N₂O emissions in maize than in miscanthus was likely explained by a synergistic effect between soil pH and N content, leading to a higher sensitivity of the N₂:N₂O ratio to changes in pH in heavily fertilized maize. Basalt amendments led to modest increases in modeled yields and the nitrogen use efficiency (i.e., fertilizer-N recover in crop production) of maize but did not affect the productivity of miscanthus. However, enhanced soil P availability maintained the long-term productivity of crops with high nutrient requirements. The alleviation of plant P limitation led to enhanced plant N uptake, thereby contributing to lower microbial N availability and N₂O emissions from crops with high nutrient requirements. Our results from the improved model suggest that the large-scale deployment of basalt, by reducing N₂O fluxes of cropping systems, could contribute to the sustainable intensification of agriculture and enhance the climate mitigation potential of bioenergy with carbon capture and storage strategies.