Effects of topsoil thickness on active organic carbon distribution in reconstruction soil filled with coal gangue

The study area was divided into four kinds of sampling plots as A ( >100 cm),B (60 -100 cm),C(40-60 cm),and D (20-40 cm) according to different topsoil thicknesses. The soil or coal gangue samples from different depths of reconstruction soil profile were collected to determine their water content ( WC),pH value,bulk density ( BD),organic carbon (SOC),microbial biomass carbon (MBC),and dissolved organic carbon (DOC). Thus the authors studied the effect of topsoil thickness on active organic carbon ( AOC) distribution. The results show that the SOC content of soil layer 0-20 cm increases 0. 48 g / kg in the test field after 5 a,while DOC and MBC average content is respectively 46. 86 mg / kg,46. 09 mg / kg. The recovery progress of organic carbon stock from the reclaimed soil in the experimental field is slower compared with other areas,which it is mainly subject to the nature of the reclamation soil and land utilization pattern. The SOC content of the same soil layer in the test zone is in relation to A>B>C>D, namely,the SOC content of the reclaimed soil filled with coal gangue also increases with the topsoil thickness increa- ses. The MBC content of soil layer 0-20 cm in the sampling plots B and C is relatively higher,that too thick or thin for topsoil thickness are not conducive to the MBC accumulation of surface soil. The DOC content of coal gangue layer in plot D is as high as 97. 90 mg / kg,and that of surface soil also reaches 64. 80 mg / kg,which is higher than that of other sampling plots. The DOC of the topsoil may be affected by coal gangue layer when the topsoil thickness is thinner. The Soil qMBC value of coal gangue layer can not accurately reflect the reconstruction soil fertility quality,but the topsoil fer- tility quality and SOC can be represented with its MBC content. MBC and pH value,BD show a significant negative correlation (p