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 mouldboard 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 extract...