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Book of Abstracts

11th IFOAM
Scientific Conference
11-15 August 1996
Copenhagen, Denmark

Abstract front page
Subject index
Athor index

Special Presentations

Soil ecology - The impact of organic and conventional agriculture on soil biota and its significance for soil fertility F3

Mäder, Paul 1, Pfiffner, Lukas 1; Lützow, Margrit von 2, Fliessbach, Andreas 1 and Munch, Jean Charles 2

1)Research Institute of Organic Agriculture, Bernhardsberg, CH-4104 Oberwil 2) GSF-Institute for Soil Ecology, Neuherberg, D-85764 Oberschleissheim

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The maintenance of soil fertility by organic manuring, crop rotation, environmentally compatible plant protection and appropriate tillage is essential in organic farming systems, because chemical fertilizers and synthetic pesticides are not used. Decomposition of plant residues and nutrient cycling are the most important soil processes related to soil fertility and stability. Soil aggregate formation by biological activity not only promotes root growth and reduces erosion damage but also facilitates soil tillage. This presentation will focus on the differential influence of organic and conventional agriculture on soil biota (microorganisms, fauna) in the temperate climate regions.

Decomposer microorganisms break down organic matter from primary production, releasing energy and mineral nutrients by enzyme catalysed metabolic processes. The microbial community is generally responsible for 90 percent of the total energy flow through soil ecosystems. There is evidence that after conversion from conventional to organic farming, the soil microflora needs ten to fifteen years to reach a new equilibrium. Microbial biomass and enzyme activities in soils under organic management were often found to be distinctly higher than in soils from conventionally cropped sites and exhibit a higher diversity. Corresponding to lower phosphorus and the lack of mineral nitrogen fertilizer input, the degree of root colonization by mycorrhizal fungi was found to be enhanced in organically managed systems, which would be expected to increase the efficiency of soil nutrient exploitation.

The most widespread ecosystem relevant activity of soil meso- and macrofauna is the decomposition of organic litter by their feeding activity. Mainly earthworms incorporate organic particles and mix them thoroughly with mineral soil in their digestive tract, enhancing humus formation, nutrient cycling, and soil structural development. In arable crops, predatory soil arthropods play an important role in the regulation of various pests. Because both earthworms and predatory soil arthropods are suitable indicators of soil fertility and habitat quality, we have put special emphasis on determining the activity and diversity of these soil animal groups under organic agriculture.