Soil microbiota are favoured by organic farming systems. Moreover they were found to need less energy fore their maintenance. The diversity of microbial functions was also increased. Our results support the hypothesis that diverse populations make better use of the available resources

Fliessbach, Andreas

Mäder, Paul

English

Organic Eprints

DOC trial: diversity and metabolic efficiency of microbial communities in organic andconventional soilsAndreas          Fliessbach   , Paul M  äderResearch Institute of Organic Agriculture (FiBL), Ackerstrasse, CH-5070 FrickKeywords: long-term trial, microbial diversity, soil functionsIntroductionOrganic farming has often been shown to improve soil fertility by increasing soil organic matter and supporting theliving organisms in the soil. Moreover it is a decisive aim of organic farming to enhance diversity in terms of timeand space. Generally diversity is looked at as the number and abundance of plants and animals living in an area.Agricultural diversity also has a temporal feature in the form of a diverse crop rotation with a large number of cropsfodder and intercrops in order to use the available resources to a large extent. The diversity of micro-organisms islargely neglected because of lack of methodology. Nowadays several methods are available to assess soil microbialdiversity. This paper aims to evaluate the effect of farming systems on soil microbial diversity and how diversityaffects functionality.Material and MethodsSoils from the DOC trial were taken in early spring from the bio-dynamic, bio-organic and the conventional systemas well as from the two unmanured control systems. Soil microbial biomass was estimated by fumigationextraction, soil respiration by CO2 evolution and microbial diversity was assessed by a substrate utilization assay.The number and intensity of substrates used served as the base for a functional diversity estimate.Results and DiscussionSoil microbial biomass was significantly affected by the farming systems, with high values in the organic systemsand lower values in the unmanured systems. Soil respiration showed minor differences between the systems, but theratio of soil respiration and microbial biomass (qCO2) was significantly lower for the biodynamic systems andshowed higher values for the unmanured conventional system (MIN) (Figure 1). We used this metabolic quotient asan indicator for the energy needed to maintain the microbial population.The diversity of microbial functions, as shown in figure 2, was found to exert the highest value in the bio-dynamicsoils, whilst the lowest values were found in the unmanured treatments. Even though these results need to be provenby other techniques they support the idea that energy use and diversity are functionally related.$ NON DYN ORG CON MIN00.511.52qCO2 [µg CO2-C mg-1 Cmic h-1]NON DYN ORG CON MIN4.14.24.3Functional diversity (Shannon H)ConclusionsSoil microbiota are favoured by organic farming systems. Moreover they were found to need less energy fore theirmaintenance. The diversity of microbial functions was also increased. Our results support the hypothesis that diversepopulations make better use of the available resources.References:Flie§bach A., M der P. (1997) Carbon source utilization by microbial communities in soils under organic andconventional farming practice. In: Microbial Communities   Functional versus Structural Approaches, eds H.Insam, A. Rangger, pp 109-120, Springer, Berlin

DOC trial: diversity and metabolic effiency of microbial communities in organic and conventional soils

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