Abstract:Based on pot experiment and isotope 15N tracer, the dynamics of soil microbial biomass nitrogenduring different corn growing stages in black soil was investigated and its biological availability was discussed The results indicated that the content of soil microbial biomass nitrogen of different treatments was different and its changes followed the similar trend during corn growing period Corn stalk and stubble rationing application of chemical fertilizer, in comparison with single application of chemical fertilizer, would result in the increase of the rate of fertilizer 15N immobilization and decrease of the rate of release of fertilizer 15N by microbes There existed significant correlations between soil microbial biomass nitrogen and soil total nitrogen, alkalihydrolysable N, corn uptake N( correlation coefficient were respectively 0.727**, 0.528* and 0.536*) Path analysis showed that the availability of soil microbial biomass nitrogen was similar to soil mineral nitrogen, above acidhydrolyzed organic nitrogen and acidinsoluble nitrogen The soil microbial biomass nitrogen was an available pool corn absorbing nitrogen from soil