This open-access article in Nature makes a surprising claim – that much better management of agricultural soil could offset a significant portion of annual carbon emissions from all sources (not just agriculture), while also being good for ecosystems and food security.

How important, in total, is this large, varied set of land-use and management practices as a GHG mitigation strategy? One of the challenges in answering this question is to distinguish between what is technically feasible and what might be achieved given economic, social and policy constraints. A comprehensive global analysis of agricultural practices combined climate-stratified modelling of emission reductions and soil C sequestration with economic and land-use change models to estimate mitigation potential as a function of varying ‘C prices’ (reflecting a social incentive to pay for mitigation). They estimated total soil GHG mitigation potential ranging from 5.3 Pg CO2(eq) yr−1 (without economic constraints) to 1.5 Pg CO2(eq) yr−1 at the lowest specified C price (US$20 per Mg of CO2(eq)). Average rates for the majority of management interventions are modest, <1 Mg CO2(eq) ha−1 yr−1. Thus, achieving large global GHG reductions requires a substantial proportion of the agricultural land base (Fig. 2). Although the economic and management constraints on biochar additions (not assessed by ref. 19) are less well known, ref. 67 estimated a global technical potential of 1–1.8 Pg CO2(eq) yr−1 (Fig. 2).

A more unconventional intervention that has been proposed is the development of crops with larger, deeper root systems, hence increasing plant C inputs and soil C sinks. Increasing root biomass and selecting for root architectures that store more C in soils has not previously been an objective for crop breeders, although most crops have sufficient genetic plasticity to alter root characteristics substantially and selection aimed at improved root adaptation to soil acidity, hypoxia and nutrient limitations could yield greater root C inputs as well as increased crop yields. Greater root C input is well recognized as a main reason for the higher soil C stocks maintained under perennial grasses compared to annual crops. Although there are no published estimates of the global C sink potential for ‘root enhancement’ of annual crop species, as a first-order estimate, a sustained increase in root C inputs might add ~1 Pg CO2(eq) yr−1 or more if applied over a large portion of global cropland area (Fig. 2).

Thus, the overall mitigation potential of existing (and potential future) soil management practices could be as high as ~8 Pg CO2(eq) yr−1. How much is achievable will depend heavily on the effectiveness of implementation strategies and socioeconomic and policy constraints.

I tried to get a quick answer on global annual emissions in Pg CO2(eq), and failed. Now I’m out of time. I’ll figure it out some other time.