The research was done in 1999 and 2000 yers. The mineralization ratio was defined according to the correlation of the number of microorganism assimilating mineral nitrogen to the ammonificator number. The general biogenity was found out defining the total number of microorganisms of the studical dominating groups during two vegetation periods. The number of microorganisms and total biogenity depend on feeding conditionns of the crops in rotation. Following the band application of phosphorus and potasium fertlizers in blue lupine the number of ammonium fixes increased 3.7 times, and that of microorganisms assimilating nitrogen 2.4 times. Application of bedding manure ar the background of the predecessor affereffect under early potato increased 5.5 times the ratio of organic matter mineralization compared to the background.