Soil, the natural medium for plant growth; soil micro-organisms; the rhizosphere and the phyllosphere; nitrogen fixation in free-living and associative symbiotic bacteria; nitrogen fixation by free-living blue-green algae; nitrogen fixation by symbiotic blue-green algae; rhizobium and legume root nodulation; actinorhizal plants (frankia-induced nodulation; organic matter decomposition; nitrification and dentrification; microbial products influencing plant growth; sulphur, phosphorus and trace element nutrition; biodegradation of pesticides and pollutants; mycorrhizae; biotechnology in agriculture.