Bio-Dynamic, bio-Organic and Conventional (integrated) agricultural systems have been compared in a randomized plot experiment (DOC-trial) in Therwil (Switzerland) since 1978. The systems differ mainly with respect to the fertilization and plant protection strategy. One additional conventional system was unfertilized in the first crop rotation period but since then it has been exclusively fertilized with mineral nutrients. Crop rotation (potatoes, winter wheat, beetroots, winter wheat and three years of grass-clover) and soil tillage are identical in all systems.
Soil microbial biomass can be regarded as a sink and a source of plant nutrients. Organic systems supported a higher microbial biomass level than conventional and unmanured systems. Accordingly, soil enzyme activities (dehydrogenase, protease, phosphatase) were distinctly higher in the organic systems. The amount of carbon dioxide respired per unit microbial biomass indicates the efficiency of resource utilization. Soil microbes from organic farming systems utilize the available resources more efficiently in terms of microbial growth rather than for maintenance.
The variety of substrates utilized by soil micro-organisms serves as an indicator of microbial functional diversity, which was higher in bio-dynamic than in conventional soils. Concomitantly, microbes in the bio-dynamic soil decomposed added plant material to a higher extent than in conventional soil with a higher proportion of the plant material being used for microbial biomass build-up.
The role of micro-organisms in P-turnover and P-availability was found to be more important in the organic systems. Additionally, mycorrhizal colonization of roots of wheat and grass clover was higher in organic than in conventional systems. Earthworm biomass, which indicates soil fertility, as well as the diversity and activity of carabids was enhanced in the organic systems.
In conclusion, soil quality as indicated by the abundance and diversity of soil organisms as well as by their activity tends to be improved under organic agriculture.
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