Traceability of compost amendment by microbial signatures

Positive effects of compost use in agriculture are well known, both on crop yield and product quality, and the use of composts as fertilizers or soil conditioner is important in the relatively large sector of organic agriculture in Austria. The underlying mechanisms of compost effects on crop quality and health, however, are not fully understood and may be related to an altered soil microbiota. The first hypothesis is linked to effects on the soil physico-chemical status and its potential role as a sink for carbon, while the other, more central hypotheses are related to the response of the soil microbial community. 1. Compost application results in an increase in soil organic carbon (soil as a C sink), and the higher the lignocellulose content is, the higher will be the increase in soil organic C. 2. Provided the nutrient supply is adequate, plant productivity is related to microbial diversity. 3. Compost application causes a long-term shift in microbial community composition. 4. Application of certain composts results in a typical microbial signature, both in terms of substrate utilisation patterns and in terms of structural markers (physiological and taxonomic imprints). The project will make use of a long-term experiment that has been established in 1992 by the Austrian Agency for Food Safety, Institute of Agrobiology, Linz. The treatments include: - Mineral nitrogen (0, 40, 80, 120 kg/ha) - Organic waste compost with and without additional mineral N - Green cut compost with and without additional mineral N - Manure compost wieth and without additional mineral N - Sewage sludge compost with and without additional mineral N This trial so far has shown that the composts have distinct effects on wheat yield and several soil chemical and physical properties. In this project, the long-term effects of composts on classical soil microbial pools and fluxes (microbial biomass and respiration) as well as microbial structural and functional parameters will be assessed. Both traditional cultivation , community level physiological profiling, and denaturing gradient gel electrophoresis and microarray technology (in both cases making use of the distinct features of 16S rDNA) will be used.

Composting is an aerobic, naturally occurring and environmentally sound process for the disposal of waste products and is of considerable economic importance. Compost as soil amendment in agriculture improves soil organic matter status. Besides the influence of compost amendments on soil carbon status and nutrient availability, little is known how composts differ in their impact on the soil microflora, which plays an important role for ecosystem functioning. In a long-term field experiment run by the Federal Agency for Food Safety since 1991, the four major compost types known in Austria, namely organic waste, green waste, manure and sewage sludge compost were applied each year after harvest on 30 m 2 plots. These treatments were further compared to mineral fertilizer only (applied in four different concentrations) and mineral fertilizer in combination with the four compost types. We determined chemical soil parameters, microbial biomass and activity as well as structure and function of the microbial communities. The results can be summarised as follows: Improvement of humus status. The organic carbon pool and total nitrogen levels in soils were increased by all compost and compost + mineral fertilizer treatments. Moreover, microbial biomass carbon was increased for urban organic waste compost, green waste compost and for all compost + mineral fertilizer plots. Increase in microbial diversity. Bacterial and fungal diversity was higher in the compost treated soils than in the control plot which corresponds to the higher plant productivity of soils treated with compost in comparison to untreated soils. Structural traces of specific composts on the microbial level. We found that some microbial groups were affected by the different composts to a different degree. Furthermore, compost amendment to soils led to different substrate utilisation patterns and thus a different functional behaviour of the investigated microorganisms. Results from this study suggest that different fertilizers, and in particular composts, do leave a specific imprint in the soil microbial community. Toolbox. The use of a multi-parameter toolbox comprising classical, physiological and molecular methods proved valuable for this project and is recommended for similar studies. Visibility. Several publications in renowned journals have increased the international visibility of our working group, and have also aided in the prolongation of the maintenance of the long-term research plots.