MICROBIAL ACTIVITY, FUNGAL ABUNDANCE, AND DISTRIBUTION OF PENICILLIUMAND FUSARIUM AS BIOINDICATORS OF A TEMPORAL DEVELOPMENT OF ORGANICALLY CULTIVATED SOILS

The present study was performed to elucidate if microbial activity, fu ngal abundance, and distribution of Penicillium and Fusarium can be us ed as bioindicators to characterize organically cultivated soils. The experimental approach was to study a potential long-term development f ollowing transition to organic farming at four farms that had been cul tivated organically for 2, 8, 11, and 31 years, respectively. Sampling was performed four times in two crops (winter wheat and leys with a m ixture of grass and leguminosae). The importance of the crop was clear ly demonstrated in the form of a significantly higher microbial activi ty in the ley soils than in the wheat soils. However, the wheat soils yielded the most consistent results and thus seem better suited for st udies of the long-term development of a bioindicator. The farms were c hosen carefully in an attempt to minimize the variations that will alw ays be present when studying different commercially run farms. These v ariations are caused by differences in e.g. soil type, soil management , fertilizer practice, and crop rotation and development. Bearing this in mind, the results showed that the abundance of the mainly soil-bor ne penicillia was significantly higher at the 'oldest' organically cul tivated farm than at the other localities, indicating a temporal devel opment during later years following transition to organic farming. The abundance of Fusarium was more variable at the genus level, but some of the species seem very promising as bioindicators, especially F. sol ani and F. equiseti, but also F. culmorum and F. labacinum. The result s also indicate a temporal development in species richness of Fusarium during the first years following transition.