AGGREGATE STABILITY AND SOIL MICROBIAL PROCESSES IN A SOIL WITH DIFFERENT CULTIVATION

A field trial was started in 1988 to examine the effects of temporary grassland and conventional tillage on aggregate stability and soil microbial processes. Different soil enzymes (actual and potential nitrification, protease, urease, xylanase, alkaline phosphatase) were selected for their importance in recycling N and P for plant nutrition, dehydrogenase and substrate induced respiration (SIR) as characteristics of microbial biomass. Analysis of seasonal patterns showed a significant (P< 0.05) increase of SIR and dehydrogenase activity in temporary grassland one year after sowing. Further development of the grassland improved protease activity, xylanase activity and aggregate stability. The following succession can be concluded from the observed results: First, temporary grassland increases microbial biomass, second, microorganisms produce enzymes, which mineralise organic compounds and at least aggregate stability increases due to the influence of microbial biomass, their activities and their by-products. After ploughing grassland in November 1990, both aggregate stability and soil microbial processes decreased rapidly. These results indicate that continuous vegetation and the activities of soil organisms are preconditions to maintain high aggregate stability.