THE INFLUENCE OF SOIL COMPACTION ON MICROBIAL BIOMASS AND ORGANIC-CARBON TURNOVER IN MICROAGGREGATES AND MACROAGGREGATES

Agricultural practices with high traffic and with low input of organic material into the soil result in the deterioration of soil structure leading to soil compaction. It is accompanied by the reduction of gas exchange and by limited colonizable habitats. The changes in microbial biomass and its activity cannot be readily explained by interactions of altered gas and water exchange. In order to explain the differences in biological activity of compacted and uncompacted soils, the soil structure related microbial turnover was observed. The content and the availability of soil organic carbon, microbial biomass and respiration activity in micro- (<0.2 mm) and macroaggregates (2-5 mm) from the plots with different wheel induced compactive treatments were measured in the layers 0- 10, 10-20 and 20-30 cm. In the topsoil (0-30 cm) of the wheel tract plot the higher content of total carbon (0.942% C(org)) and higher availability of C than in the no traffic (0.907% C(org)) and high traffic (0.908% C(org)) plots were established. The compacted plots contained less total carbohydrates in macroaggregates. The average value of microbial biomass was lower only in the high traffic plot - 99 mug C g-1 against 159 in the no traffic plot. The compacted plots differed from the other treatments in the distribution of microbial biomass in soil layers; the maximum of microbial biomass was in the lower layers (20-30 cm) instead of in the surface layer. The ''potential'' activity of microbial biomass reached maximal values in the high traffic plot.