No-tillage effects on soil CH4 fluxes: A meta-analysis

No-tillage (NT) has widely been promoted as a conservation practice that also offsets agriculture-driven greenhouse gases and boosts agroecosystem performance. While most studies have focused on the effects of no-till on nitrous oxide and carbon dioxide fluxes, much less attention has been paid to the impacts on methane (CH4) emissions. We conducted a meta-analysis to determine whether tillage management (conventional till, CT vs. NT) affects soil CH4 fluxes, and what management and environmental conditions regulate the effect. The regulating factors we identified include crop, climatic zone, soil class and experiment age (i.e. years since beginning NT). Our study included 41 papers, with a total number of 90 case studies, that covered arable lands of all five continents. On average, NT significantly decreased CH4 emissions from paddy fields, from 12.39 to 9.55 mg m-2 h-1 (p < 0.05). Conversely, NT showed a slight but non-significant tendency to increase CH4 emissions in maize-cultivated fields, from an average of -0.15 mg m- 2 h-1 of CT to 0.05 mg m- 2 h-1 of NT. Other factors moderating the NT effect - like climate, soil, or years since the conversion to NT management - had weak regulation on soil CH4 emissions, with the exception for a slight tendency (not significant) of NT to reduce emissions in humid subtropical climate, with average CH4 fluxes of 3.90 mg m- 2 h-1 vs. 5.01 mg m-2 h-1 of CT. However, we found that the effect of climate is often confounded by choice of crop, and thus should be interpreted with caution. While NT is used for many other soil benefits, our results indicate that the effect on CH4 emissions in dryland crops is nonexistent or weak in the investigated literature. However, considerable CH4 emission reduction is possible for rice production or other production systems that use flooded soils.

Automated summary

No-tillage management significantly decreased CH4 emissions in paddy fields, but showed a slight non-significant tendency to increase emissions in maize-cultivated fields. Factors like climate, soil, and years since conversion to NT management had weak regulation on CH4 emissions, with a slight reduction tendency in humid subtropical climate. Climate effects were often confounded by crop choice and should be interpreted cautiously.