title: Biochar has no effect on soil respiration across Chinese agricultural soils.
abstract: Biochar addition to soil has been widely accepted as an option to enhance soil carbon sequestration by introducing recalcitrant organic matter. However, it remains unclear whether biochar will negate the net carbon accumulation by increasing carbon loss through CO2 efflux from soil (soil respiration). The objectives of this study were to address: 1) whether biochar addition increases soil respiration; and whether biochar application rate and biochar type (feedstock and pyrolyzing system) affect soil respiration. Two series of field experiments were carried out at 8 sites representing the main crop production areas in China. In experiment 1, a single type of wheat straw biochar was amended at rates of 0, 20 and 40 tha(-1) in four rice paddies and three dry croplands. In experiment 2, four types of biochar (varying in feedstock and pyrolyzing system) were amended at rates of 0 and 20 tha(-1) in a rice paddy under rice-wheat rotation. Results showed that biochar addition had no effect on CO2 efflux from soils consistently across sites, although it increased topsoil organic carbon stock by 38% on average. Meanwhile, CO2 efflux from soils amended with 40 t of biochar did not significantly higher than soils amended with 20 t of biochar. While the biochars used in Experiment 2 had different carbon pools and physico-chemical properties, they had no effect on soil CO2 efflux. The soil CO2 efflux following biochar addition could be hardly explained by the changes in soil physic-chemical properties and in soil microbial biomass. Thus, we argue that biochar will not negate the net carbon accumulation by increasing carbon loss through CO2 efflux in agricultural soils.
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095, China. Electronic address: xiaoyuliu@njau.edu.cn.
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Liu
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095, China. Electronic address: zhengjufeng@njau.edu.cn.
authors.forename: Jufeng
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095, China. Electronic address: 593148086@qq.com.
authors.forename: Dengxiao
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095, China. Electronic address: kuncheng@aliyun.com.
authors.forename: Kun
authors.initials: K
authors.lastname: Cheng
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China. Electronic address: 867799632@qq.com.
authors.forename: Huimin
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China. Electronic address: af-725@163.com.
authors.forename: Afeng
authors.initials: A
authors.lastname: Zhang
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095, China. Electronic address: lqli@njau.edu.cn.
authors.forename: Lianqing
authors.initials: L
authors.lastname: Li
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; School of Materials Science and Engineering, University of New South Wales, NSW 2052, Australia. Electronic address: joey.stephen@gmail.com.
authors.forename: Stephen
authors.initials: S
authors.lastname: Joseph
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Institute of Biological and Environmental Sciences, University of Aberdeen, 23 St Machar Drive, Aberdeen AB24 3UU, UK. Electronic address: pete.smith@abdn.ac.uk.
authors.forename: Pete
authors.initials: P
authors.lastname: Smith
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Department of Environmental Sciences, University of California Riverside, CA 92521, USA. Electronic address: crowley@ucr.edu.
authors.forename: David
authors.initials: D
authors.lastname: Crowley
authors.affiliation: Department of Soil Science of Temperate Ecosystems, University of Göttingen, Büsgenweg 2, Göttingen 37077, Germany; Department of Agricultural Soil Science, University of Göttingen, Büsgenweg 2, Göttingen 37077, Germany. Electronic address: kuzyakov@gwdg.de.
authors.forename: Yakov
authors.initials: Y
authors.lastname: Kuzyakov
authors.affiliation: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, China; Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing 210095, China; Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration, Zhejiang A & F University, Lin'an, Hangzhou 311300, China. Electronic address: pangenxing@aliyun.com.
authors.forename: Genxing
authors.initials: G
authors.lastname: Pan
mesh_terms: D000383:Agriculture / Q000379:methods*; D002606:Charcoal / Q000737:chemistry*; D002681:China; D005308:Fertilizers; D012987:Soil / Q000737:chemistry*
chemical_list: D005308:Fertilizers; D012987:Soil; C540010:biochar; D002606:Charcoal
keywords: Agricultural soils; Biochar; Carbon stability; Greenhouse gas mitigation; Microbial activity; Soil respiration