Exploring the potential of soil amendments for climate change mitigation strategies and soil health in Californian rangelands

Abstract:

Soil amendment technologies hold substantial potential for capturing CO₂ and sequestering C into the soil, while benefiting agricultural productivity and land sustainability. Of particular promise is the application of pulverized ground rock from industrial waste that can sequester carbon through enhanced weathering. In this study, we explored the biogeochemical effects of ground rock amendments on Californian rangeland soils, including their effect on soil greenhouse gas emissions with cavity ring-down spectroscopy and automated static chambers, net primary productivity, and soil carbon and nitrogen dynamics. We compared replicated rock amended plots with sites receiving compost amendments, and with untreated controls. Treated plots were separately amended with 57.4 t/ha compost or 46.6 t/ha of basaltic ground rock. Preliminary analyses indicated that soil CO₂ fluxes over the 2019/2020 growing season were significantly reduced by compost (1.92 ± 0.12 umol/m²/s) and ground rock (1.95 ± 0.10 umol/m²/s) amendment when compared to control (2.16 ± 0.10 umol/m²/s; p <0.001). Furthermore, the global warming potential (CO₂-e; based on cumulative greenhouse emissions of CO₂, N₂O and CH₄ over the growing season) of soils with ground rock amendments were reduced by 30% compared to control (p <0.1). This was mostly due to reductions in N₂O emissions, which may relate to direct N₂O reduction or impacts of ground rock amendments on nitrification rates. Global warming potential of soil did not significantly change with compost amendment. Further analyses of carbon allocation into aboveground biomass and inorganic and organic soil carbon will reveal the entire climate-benefit of these amendment strategies.