Can deep tillage enhance carbon sequestration in soils? A meta-analysis towards GHG mitigation and sustainable agricultural management

Sequestration of soil organic carbon (SOC) is regarded as a promising approach to offset global CO2 emissions. Deep tillage (DT) can alleviate high soil strength, influencing both the surface and subsoil carbon pools either directly or indirectly. However, field studies on the benefits of DT to SOC remain inconclusive, and comprehensive quantitative assessment has been lacking. This study used meta-analysis to assess the response of SOC storage to DT based on global data of 430 comparisons from 43 studies. In general, DT was found to significantly enhanced SOC by 7.79%. Specifically, subsoiling significantly increased SOC, augmenting it by 8.87%. Deep ploughing did not facilitate SOC sequestration to a significant extent for the whole soil profile, although it did significantly increase SOC in 20-50 cm layer. The individual response of SOC to DT was found to be highly site-specific. DT was found to bring greater benefits in soil under arid zones, which typically featured fine or medium textured soil, and relatively high background SOC (> 6 g kg(-1)) and BD content (> 1.3 g cm(-3)). Furthermore, agronomic practices played an essential role in constraining SOC responses to DT, where better SOC responses were observed under rotational cropping, DT/NT (no-tillage) rotational tillage, advisable DT depth difference, and moderate nitrogen application rate (200-300 kg ha(-1) y(-1)) with prolonged experiment duration. In this regard, it is important to include site-specific environmental and agronomic conditions when identifying appropriate DT practices for enhancing SOC sequestration. The investigation into SOC storage capacity and DT technologies can provide scientific policy guidance for long-term global carbon management.