Opportunities and Challenges of Soil Carbon Sequestration by Conservation Agriculture in China

Conservation agriculture (CA), an emerging technology for sustainable agriculture, has been practiced in China for more than 30 years and is increasingly being adopted on cropland. CA system has four components: (i) no-till (NT), (ii) residue mulch, (iii) complex/diverse cropping system, and (iv) integrated nutrient management. Conservation tillage (CT, main technology of CA) methods, relevant to a range of cropping systems, are practiced on 6.67 million hectare (Mha) in China. With growing concerns about global warming, soil organic carbon (SOC) sequestration is an important strategy to offset anthropogenic emissions. This chapter collates and synthesizes available research literature on SOC sequestration under different tillage systems in China. Specific focus is on the SOC dynamics, SOC stock, rate of SOC sequestration, and soil quality under different tillage systems in diverse agroeco regions. The research on a effects on SOC sequestration has been conducted in China for more than 20 years since the 1990s. The review of the literature indicates that NT can increase SOC concentration in the surface layer under dryland farming and rice (Oryza sativa L.) paddy soils. The average rate of increase of SOC (g kg(-1) year(-1)) in 0-20 cm depth under NT systems is 0.60-3.74, 0.14-4.15, 0.50-5.94, and 8.81-17.95 for the Northeast, North, Northwest, and paddy fields of Southern China, respectively. However, most research results indicate that SOC under NT is concentrated more in the surface soil (8.6-31.3 g kg(-1) in NT vs. 5.3-26.8 g kg(-1) in plow tillage (PT)) and is relatively less in the subsoil (6.9-17.6 g kg(-1) in NT vs. 10.2-24.5 g kg(-1) in PT). Residue management is the key factor in SOC sequestration, which also influences SOC dynamics. Cropping system and rotation also affect SOC sequestration. Further, NT can improve soil quality by enhancing and stabilizing aggregation. Because of relatively short duration, soil processes under CA management are not clearly understood and are confounded by the diverse cropping systems. There is a need to study pedospheric processes affecting SOC sequestration and soil quality under long-term use of CA in diverse cropping systems and complex agroeco regions of China. Potential and limitations of CA, and research priorities in China are discussed.