Soil management for sustainable rice production in the tropics

The first part of the review deals with the components of the ecosystem (floodwater, photosynthetic aquatic biomass, and fauna), their properties and activies. Variations of the major physical and chemical properties of the floodwater (temperature, pH, 02 concentration, N content...) during the crop cycle are summarized. The section on photosynthetic aquatic biomass considers composition, nutrient contribution, and effects on N dynamics, namely : biological N2 fixation, N immobilization, N recycling, N accumulation at the soil surface, N supply to rice crop, and N losses by NH3 volatilization in relation to pH increase due to photosynthetic activity in the floodwater. The section on fauna emphasizes grazing and nutrient recycling by ostracods and snails, and the role of tubificid worms on floodwater ecology. The second part deals with the agronomic management of the floodwater ecosystem. It reviews cultural practices that take advantage of the agronomic potential of the floodwater ecosystem (decreasing losses due to NH3 volatization, promoting photodependent BNF, recycling of nutrients), and the effects of crop intensification on floodwater ecology and possible related effects on soil fertility. (Résumé d'auteur