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No-till is often referred to as a climate change mitigation option, possibly with a stronger conviction, than as a practice to manage soil organic C (SOC) content. We conducted a global meta-analysis to evaluate the effect of no-till (NT) on SOC concentration (SOC c , g C kg−1 soil) and stock (SOC s , Mg C ha−1 land) across climate, soil texture, cropping systems, and no-till duration to appraise the priority-setting. Compared to conventional tillage, NT favoured a significant rise (ΔSOC c) of 38% in the 0–5 cm soil layer and a much lesser 6% increase in the 5–10 cm layer and no change beyond 10 cm. The temperate climate had nearly twice ΔSOC c in the 0–5 cm layer compared to other climates, while the tropical climate favoured sub-surface accumulation. Coarse- and medium-textured soils and the inclusion of legumes in crop rotation facilitated larger positive ΔSOC s under NT. The microbial biomass C was the most abundant C pool, with 61% and 23% increases under NT in 0–5 and 5–10 cm layers. A large ΔSOC c in aggregates also characterized the top 0–5 cm layer. The difference in SOC s was realized to a maximum 30 cm depth (5.4 Mg ha−1 or 14%) in favour of NT, although varying with the duration of its adoption. The contribution of NT in mitigating global anthropogenic greenhouse gas emissions is meagre, although it can substantially offset emissions from agriculture (17–58%). The benefit of NT in improving SOC is primarily restricted to the surface layer, which is potentially exposed, and therefore an increase could be short-lived. Nevertheless, a short-term gain in SOC is likely to enhance soil quality and crop productivity. Thus, NT may be promoted as a sustainable agricultural management practice rather than emphasizing its role as a potential climate change mitigation option. • No-till increased ∼38% SOC concentration in 0–5 cm layer. • SOC stock increased by 14% or 5.4 Mg C ha−1 over 0–30 cm soil profile. • Tropical climate had net SOC gain at > 20 cm depth. • Microbial biomass C and soil aggregate-associated C had greater increases under no-till in 0–5 cm. • Contribution of no-till to global climate change mitigation is trivial, although it can offset GHG emissions from agriculture. [ABSTRACT FROM AUTHOR]

No-till (NT) has been widely regarded as a potential option to enhance soil organic carbon (SOC) sequestration and thus mitigate climate change. However, recent studies have shown that previous estimates of SOC storage under NT seem to be overestimated due to shallow sampling and improper SOC accounting. In China, the overall trend and magnitude of changes in SOC storage in response to NT adoption remain inconclusive. Here we use a meta-analysis to assess the relative change in SOC storage (profiles ≥20 cm) based on 95 comparisons between NT and conventional tillage (CT) from 57 experimental sites (≥3 years) covering various cropping systems, soil types, and climatic regions of China. The results revealed that compared to CT, adopting NT led to SOC accumulation in the upper 20 cm layer and SOC depletion in the 30–40 cm layer. On average, NT improved SOC stocks over CT by 3.8% [95% confidence interval (CI): 1.4%–6.3%; P = 0.005] and 5.1% (95%CI: 2.5%–7.7%; P < 0.001) as represented by the equivalent soil mass (ESM) and fixed-depth (FD) approaches, respectively. The relative change in SOC storage rate under NT over tilled soil for the top 30 cm layer was therefore significantly higher ( Mean : 0.300 Mg ha −1 yr −1 , 95%CI: 0.054–0.547; P < 0.001) calculated by FD approach than that by ESM ( Mean : 0.141 Mg ha −1 yr −1 , 95%CI: −0.102–0.384; P = 0.100). Further analysis suggested that the effect of NT on SOC storage was significant with residue retained‎, double cropping systems, and in the coarse textured soils. We conclude that although NT was an effective agronomy option for soil conservation in China, the potential for mitigation climate change through increased SOC sequestration by NT should not be amplified. [ABSTRACT FROM AUTHOR]

There has been a careless use of terminology like “climate change mitigation” and “mitigate global warming” in scientific papers on no-tillage management in agriculture. This is because it has yet to be shown unequivocally that no-tillage can lead to carbon (C) sequestration let alone climate change mitigation. I briefly summarize evidence that shows that the claims of climate change mitigation through no-tillage agriculture are highly overstated. [ABSTRACT FROM AUTHOR]