[Impact of tillage practices on microbial biomass carbon in top layer of black soils].

A study was conducted on a long-term (13 years) tillage and rotation experiment on black soil in northeast China to determine the effects of tillage, time and soil depth on soil microbial biomass carbon (MBC). Tillage systems included no tillage (NT), ridge tillage (RT) and mould-board plough (MP). Soil sampling was done at 0-5, 5-10 and 10-20 cm depths in June, August and September, 2013, and April, 2014 in the corn phase of corn-soybean rotation plots. MBC content was measured by the chloroform fumigation extraction (CFE) method. The results showed that the MBC content varied with sampling time and soil depth. Soil MBC content was the lowest in April for all three tillage systems, and was highest in June for MP, and highest in August for NT and RT. At each sampling time, tillage system had a significant effect on soil MBC content only in the top 0-5 cm layer. The MBC content showed obvious stratification under NT and RT with a higher MBC content in the top 0-5 cm layer than under MP. The stratification ratios under NT and RT were greatest in September when they were respectively 67.8% and 95.5% greater than under MP. Our results showed that soil MBC contents were greatly affected by the time and soil depth, and were more apparently accumulated in the top layer under NT and RT.