Studies on the comparison of microbial and biochemical characteristics of soils were based on a field experiment established in 1994 at the IUNG Experimental Station in Osiny on soil (loamy sand) belonging to complex IV. In this experiment spring barley and winter wheat were grown in three crop production systems: ecological, integrated and conventional. Soil under wheat were analysed in 1996, 1997 and 1998, and under barley in 1997 and 1998. Microbial biomass, numbers of bacteria and fungi, soil respiration and enzymes (dehydrogenase, phosphatases) activity were generally higher in the soil under the rested cereals grown in the ecological system than in the soil under these crops grown in the conventional or integrated system. These differences were detected during all three growing seasons, indicating long-lasting changes in the biological characteristics of the studied soil.