Microorganisms and soil fauna make an important contribution to the conversion of organic matter in the soil. This research project investigates the relation between the diversity of crops and cultivation methods above ground and the biodiversity of organisms below ground, and evaluates the significance of this for the life support functions of the soil, such as the retention of nutrients and the suppression of diseases.
We have recently found indications that reduced fertilisation and tillage of agricultural soils allows fungi to play a greater role in the soil ecosystem and leads to a more natural soil fauna. It is not yet clear what the implications of a dominant fungal population are for soil fauna such as earthworms, which also play a major role in mineralisation. If the fungal population increases rapidly while the availability of nutrients is lower, the fungi/bacteria ratio may be useful as an indicator for sustainability. The existing populations of soil animals, such as nematodes, enchytraeid worms (potworms), microarthropods and earthworms, may also be signifi cant in this regard.
Sustainable functioning of the soil ecosystem
The aim of our research is to help promote the sustainable functioning of the soil ecosystem, based on knowledge of the functional biodiversity of microorganisms and the soil fauna. The core topics are:
- clarifying the relations between soil biodiversity and sustainable agriculture, particularly nutrient cycles
- identifying groups of organisms and/or functions which are most numerous or active in agricultural soils with limited nutrient losses
- developing sensitive and practical biological in dicators for healthy soils and sustainable farm management
- identifying cultivation measures that have a positive effect on the diversity and quality of the soil life and the natural soil fertility
Various research methods are used, such as fungi/ bacteria ratios, bacteria and fungi activity, number and diversity of microarthropods and earthworms, and potential mineralisation. The results are compared with available field data on tillage, fertilisation, nutrient balance and leaching, and with various reference situations. New molecular techniques are also being developed, including the use of microarrays.
We have developed biological indicators of soil quality which are used in field projects and in the Soil Biological Indicator for the National Soil Quality Monitoring Network. The results reveal large differences between various categories of soil type and land use, and significant effects of farm management on most groups of organisms. The largest proportion of the measured biomass consists of bacteria. This biomass is high in grassland, lower in arable land and very low in horticultural soils. Across the same series of soils, the species composition of microarthropods varies in a way that reflects an increasing intensity of use: the diversity of nematodes changes and bacterial activity rises as the intensity of use increases (measured in livestock units per hectare).
The biomass, activity and diversity of the soil organisms tends to be higher on organic and extensive farms, where the soil fauna is less disturbed and soil fertility is significantly higher (50% higher potential N mineralisation). Observations on several experimental farms indicate an increase in fungal biomass under more extensive management regimes. A book on microbiological methods for assessing soil quality has been compiled as part of the EUCOST Action 831, with contributions from about 50 authors from various European countries.