Soil carbon-food synergy: sizable contributions of small-scale farmers

BackgroundBenefits to agricultural yield improvement, soil degradation prevention, and climatemitigation are central to the synergies of soil organic carbon (SOC) build-up. However,the contributions of small-scale farmers, the main target of recent agricultural and ruraldevelopment policies, to SOC enhancement are understudied. Here, we present aglobal analysis of small-scale farmers contributions to the potential of additional SOCstocks and the associated increase in crop production.MethodsWe applied a machine learning technique, random forest, to global gridded datasets oncrop yield (wheat, maize, rice, soybean, sorghum and millet), soil, climate andagronomic management practices from the 2000s. Using the established crop-specificSOC-yield relationships, the potentials of additional SOC build-up and crop productionincrease were simulated. The estimated SOC increase was converted into globaldecadal mean temperature change using the temperature sensitivity to cumulative totalanthropogenic CO2 emissions from preindustrial levels. The amount of inorganicnitrogen (N) input that would result in the same yield outcome as the SOC build-up wasderived from the crop-specific N-yield relationships.ResultsSOC contributes to yields in addition to management and climatic factors. AdditionalSOC sums up to 12.78 GtC (11.5514.05 GtC) of global SOC stock, which earns 38.24Mt (22.8857.48 Mt) of additional crop production and prevents warming by 0.030 C(0.0190.041 C). This production increase equates to what would be achieved by aninorganic N input of 5.82 Mt N (3.897.14 Mt N). Small-scale farmers account for 28%(2630%) of the additional SOC build-up and 17% (1520%) of the productionincrease. Key crops and regions in terms of small-scale farmers contributions includeSub-Saharan African maize and rice, Latin American and Caribbean soybean andmaize, and South Asian rice and wheat.ConclusionsThe contribution of small-scale farmers to the potential increase in SOC stock and cropproduction is sizable, which in theory further leads to saving inorganic N input. Thesefindings emphasize the importance of linking soil management to sustainable land andclimate mitigation with institutions and policy for small-scale farmers. Such a joint policywould assist multiple development goals.