Although yields from organically managed production systems are lower in general than those from conventional agricultural systems, there are advantages in organic farming in terms of lower energy, fertilizer and pesticide inputs, optimized nutrient utilization, better soil quality, and a lower environmental impact. Higher levels of faunal and floral biodiversity have been found in organically managed farms, but for microbial diversity controversial data is available. One reason for these problems are the methods used for determination of microbial diversity. However, beside qualitative differences in microbial community structures most of the studies show a higher microbial biomass, a higher microbial species richness, a higher biodiversity based on diversity indices and a higher microbial evenness in organic systems. Many plant associated microorganisms are known to have plant beneficial traits. Little is known about the relationship between microbial diversity, plant health and plant growth, and the impact of management on this functional group. Interestingly, results from novel studies indicate an enhancement of plant beneficial microorganisms by organic farming. As an example for this phenomenon the enrichment of microorganisms antagonistic towards plant pathogens in organic vineyards is depicted.
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