In silico assessment of the potential of basalt amendments to enhance the climate mitigation potential of Bioenergy with Carbon Capture and Storage strategies

Abstract:

Bioenergy with carbon capture and storage (BECCS) is a key strategy for climate mitigation. However, non-CO₂ climate forcing from fertilizer derived N₂O emissions calls into question its efficacy. 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 control and basalt amended maize (Zea mays) and miscanthus (Miscanthus x giganteus) to improve the nitrogen (N) module of the DayCent biogeochemical model and evaluate the potential of basalt amendments to reduce N losses, increase yields, and reduce the non-CO₂ climate forcing from two important 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, and lowered the N₂O emission factor (i.e. fertilizer induced N₂O release to the atmosphere) by 17% and 11%, respectively. 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 the 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 the N₂O EF of cropping systems, could contribute to the sustainable intensification of agriculture and significantly enhance the climate mitigation potential of BECCS strategies.