Includes appendix, bibliographical references and index.

Introduction -- Soil : the natural medium for plant growth -- Soil microorganisms -- 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 denitrification -- Microbial products influencing plant growth -- Sulphur, phosphorus and trace element nutrition -- Biodegradation of pesticides and pollutants -- Mycorrhizae -- Biotechnology in agriculture.