The agricultural value of sewage sludges is well known and a lot of published data has demonstrated the positive effects of sludge appli cations on plant growth and yield. These effects are probably due mainly to the nitrogen and phosphorus content of sewage sludges. But, as sludges are more organic than mineral, we can expect an effect of the organic matter added to the soil on soil fertility. Certainly, in the future, landspreading of sludges will be regulated, taking into account pollution hazards for waters (excess of nitrogen and phosphorus supply compared to plant needs and soil storage capacities) and for soils (excess of heavy metals supply and build up in soils). There will be regulations fixing what low level of sludges may be spread each year, decreasing their comparative value with respect to mineral fertilizers. In this eventuality, the organic value of sludges will take on a greater importance and several questions arise : - what is the lowest amount of sludge to be spread to have an immediate effect on soil physical properties? - are sludges effective on soil physical properties when spreading repeated low amounts? On the other hand, organic matter and soil biology are closely linked and there are few data on the possible effects - beneficial or detrimenta- on soil organisms.

Proceedings of a Seminar organized jointly by the Commission of the European Communities, Directorate-General for Science Research and Development and the Bayerische Landesanstalt für Bodenkultur und Pflanzenbau, Munich, F.R.G., June 23-24, 1982

Inhalt
Session 1 Effects of Sewage Sludges on Soil Physical Properties.- Increasing organic matter of soils by sewage sludge.- The analysis of nitrogen and humus in connection with a field test for the fertilization with straw and sewage sludge.- Influence of limed sludge on soil organic matter and soil physical properties.- Some effects of sewage sludge on soil physical conditions and plant growth.- General comments on the organic value of sludge.- Influence of sewage sludge application on physical properties of soils and its contribution to the humus balance.- Influence of increasing amounts of sewage sludge on the soil structure.- The influence of the agricultural utilization of domestic sewage sludge on the quality of the soil.- Physical properties in sewage sludge and sludge treated soils.- Modifications of some physical and chemical soil properties following sludge and compost applications.- Session 2 Effects of Sewage Sludges on Soil Biological Properties.- Effect of sewage sludge on soil humus content.- Influence of sewage sludge application on organic matter content, micro-organisms and microbial activities of a sandy loam soil.- Influence of sewage sludge application on microarthropods (collembola and mites) and nematodes in a sandy loam soil.- Soil microbial activities as affected by application of composted sewage sludge.- Side effects of sewage sludges: possible enhancement of denitrification.- Land application of sludge: effects on soil microflora.- Sludge effect on soil and rhizosphere biological activities.- Some biological properties in sewage sludge and sewage treated soils.- List of Participants.- Index of Authors.