Response of soil microbial biomass and activity to agricultural de-intensification over a 10 year period

Soil microbial properties. such as microbial biomass and microbial activity, are suitable indicators to predict soil biological status as a part of soil fertility after transition from high-input agricultural systems to low-input systems. These criteria were applied to evaluate how agricultural de-intensification as practiced by the integrated farming system (IFS) of Germany differ from the conventional agricultural system (CFS) over long-term investigation. The study was multi-factorial, covering agricultural management, spatial as well as temporal variability. Therefore, the research included nine different locations with a wide range of soil types, soil textures of the top horizons, parent materials, climatic conditions, along with the individual impact of farmers over a ten year period. In sum, the mean pH values, the mean amounts of microbial biomass (estimated from maximal initial responses) and soil organic matter, mean C-mic-to-C-org ratio, and mean dehydrogenase activity of the nine locations were almost identical in both systems. The amounts of soil organic matter, microbial biomass and C-mic-to-C-org ratio increased 10-15% in the integrated management treatment compared with the conventional management system starting from the fifth year of investigation. Conversely, during the first 4 years of the investigation the examined parameters were slightly increased in the conventional management system. The differences in dehydrogenase activity between both systems changed from year to year. No differences between both systems were found for the pH values of the investigated soils. Beyond that, the factor soil texture of the top horizon (expressed as the clay content) was highly significant for the amounts of the investigated parameters, During the 10 year investigation period, differences between both management systems in particular years were related to the cultivation of intermediate crops and conservation tillage practices. (C) 2001 Elsevier Science Ltd. All rights reserved.