title: Change in soil organic carbon between 1981 and 2011 in croplands of Heilongjiang Province, northeast China.
abstract: BACKGROUND
  Soil organic carbon (SOC) is fundamental for mitigating climate change as well as improving soil fertility. Databases of SOC obtained from soil surveys in 1981 and 2011 were used to assess SOC change (0-20 cm) in croplands of Heilongjiang Province in northeast China. Three counties (Lindian, Hailun and Baoqing) were selected as typical croplands representing major soil types and land use types in the region.
  
  
  RESULTS
  The changes in SOC density (SOCD) between 1981 and 2001 were -6.6, -14.7 and 5.7 Mg C ha(-1) in Lindian, Hailun and Baoqing Counties respectively. The total SOC storage (SOCS) changes were estimated to be -11.3, -19.1 and 16.5% of those in 1981 in the respective counties. The results showed 22-550% increases in SOCS in rice (Oryza sativa L.) paddies in the three counties, but 28-33% decreases in dry cropland in Lindian and Hailun Counties. In addition, an increase of 11.4 Mg C ha(-1) in SOCD was observed in state-owned farms (P < 0.05), whereas no significant change was observed in family-owned farms.
  
  
  CONCLUSIONS
  Soil C:N ratio and initial SOCD related to soil groups were important determinants of SOCD changes. Land use and residue returning greatly affected SOC changes in the study region. To increase the topsoil SOCD, the results suggest the conversion of dry croplands to rice paddies and returning of crop residue to soils.
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Lu-Jun
authors.initials: LJ
authors.lastname: Li
authors.affiliation: Department of Land, Air and Water Resources, University of California, Davis, Davis, CA, 95616, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Burger
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Shu-Li
authors.initials: SL
authors.lastname: Du
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Wen-Xiu
authors.initials: WX
authors.lastname: Zou
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Meng-Yang
authors.initials: MY
authors.lastname: You
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Xiang-Xiang
authors.initials: XX
authors.lastname: Hao
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Xin-Chun
authors.initials: XC
authors.lastname: Lu
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Mollisols Agroecology, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin, 150081, China.
authors.forename: Xiao-Zeng
authors.initials: XZ
authors.lastname: Han
mesh_terms: D000383:Agriculture / Q000379:methods; D002244:Carbon / Q000032:analysis*; D002681:China; D057231:Climate Change; D018556:Crops, Agricultural / Q000254:growth & development*; D004784:Environmental Monitoring; D009584:Nitrogen / Q000032:analysis; D012275:Oryza / Q000254:growth & development; D012987:Soil / Q000737:chemistry*; D013025:Glycine max / Q000254:growth & development; D003313:Zea mays / Q000254:growth & development
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen
keywords: black soil; carbon storage; crop residue returning; land use; soil organic carbon density; state farm