Abstract
Abstract One of society’s greatest challenges is sequestering vast amounts of carbon to avoid dangerous climate change without driving competition for land and resources. Here we assess the potential of an integrated approach based on enhancement of natural biogeochemical cycles in agro-ecosystems that stimulate carbon capture and storage while increasing resilience and long-term productivity. The method integrates plant photosynthesis in the form of (cover) crops and agroforestry, which drives carbon capture. Belowground plant-carbon is efficiently stored as stable soil organic carbon. Aboveground crop and tree residues are pyrolyzed into biochar, which is applied to the soil reducing carbon release through decomposition. Enhanced weathering of basalt powder worked into the soil further captures and stores carbon, while releasing nutrients and alkalinity. The integrated system is regenerative, through enhanced virtuous cycles that lead to improved plant capture, biomass storage and crop yield, the prerequisites for large-scale carbon sequestration along with food security.
Highlights
Human-induced climate change has significant adverse impacts on our environment, economy, and way of life
Examples include (1) boosting the growth and standing carbon stock in plants in cropping and pasture systems through cover- and inter-cropping; (2) reestablishing and/or enhancing soil organic carbon (SOC) stocks 10; (3) production of biochar, which is plant biomass transformed at elevated temperatures under oxygen-limited conditions into a recalcitrant form that withstands decomposition for many decades/centuries to possibly even millennia 11; and (4) increasing the inorganic carbon sink in soils via Mg and Ca silicate weathering by working finely ground rock into soils 12
The combined global carbon sequestration potential of such measures has been estimated at 0.3-6.8 Gt C yr-1 13
Summary
Plants are the central players in the assessed land-based carbon sequestration system (Figure 1). Microorganisms degrade plant carbon (respiring CO2), and foster conversion into stable forms of SOC 30,31 (Figure 2a) Both processes are affected by the activity, abundance, and community composition of microorganisms and are soil dependent 32. Besides biomass input and the availability of sink strength, stable SOC accumulation depends on the conversion efficiency of plant carbon into SOC, here defined as the carbon sequestration efficiency (CSE) (Figure 2), and the rate of SOC degradation [34,35]. The process results in an initial release of ~45% of the plant carbon stored in agricultural and forestry residues (mean over different temperatures) 38 and, in greater carbon emissions in the first few years of biochar production, relative to regular biomass decomposition (negative values in Sup Figure 1). We infer that limited on-site availability of biomass residues in agriculture and neighbouring forestry systems will initially enable biochar application rates of ~0.5-1 t ha-1 yr-1, which corresponds to ~0.37-0.73 t C ha-1 yr-1 (at a mean biochar carbon content of 73% 38)
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