Intensification Of No-Till Agricultural Systems: An Opportunity For Carbon Sequestration

The "4 per 1,000" initiative was launched at the 21st Conference of the Parties (COP21) stimulating a long-standing debate on the potential of no-till (NT) to promote soil C sequestration. Previous reviews found little or no soil organic C (SOC) accrual in NT soils as compared with full inversion tillage when soils are sampled deeper than 30 cm. Here, we present the results of a global meta-analysis of studies assessing SOC and total N (TN) storage and dynamics in NT and tilled soils from the most important agricultural regions of the world. Overall, our results show that NT soils stored 6.7 +/- 1.9 Mg C ha(-1) and 1.1 +/- 0.4 Mg N ha(-1) more than tilled soils (0-to-100-cm depth) with an average of 16 yr of NT, in contrast with previous findings. However, C sequestration (+4.7 +/- 1.9 Mg C ha(-1) in the 0-to-60-cm depth with an average of 11 yr of NT) depended on the association of NT with increased crop frequency and the inclusion of legumes cover crops. Single-cropping systems lack the necessary C inputs to offset SOC losses in the soil profile (below 30-cm depth). However, double-cropping systems decreased soil TN that may constrain future C sequestration. The use of legumes alleviated TN loss and supported soil C sequestration. Briefly, our findings indicate that NT can avoid SOC losses from tilled soils, partially offsetting CO2 emissions from agriculture. Moreover, NT with agricultural intensification can promote soil C sequestration, thus contributing to soil quality, food security, and adaptation to climate change.