Biology and management of the floodwater ecosystems in ricefields
1996
Roger, P.A. (International Rice Research Inst., P.O. Box 933, Manila 1099 (Philippines))
The first part of the book describes the components of the ecosystem (floodwater, photosynthetic aquatic biomass, and fauna), their properties, and activities. Variations of the major physical and chemical properties of the floodwater (temperature, pH, O2 concentration, N content) during the crop cycle are summarized. The section on photosynthetic aquatic biomass considers its components, composition, nutrient contribution, and effects on N dynamics, namely biological N2 fixation, N immobilization, recycling, accumulation at the soil surface, supply to the rice crop, and N losses by NH3 volatilization in relation to pH increase due to photosynthetic activity in floodwater. The section on fauna considers the nature of the components, their dynamics during the crop cycle, and their major activities: 1) grazing and nutrient recycling by primary consumers (zooplankton, snails), 2) nutrient translocation and recycling by aquatic oligochaete worms, and 3) the detrimental effects of the fauna on rice and as vectors of human diseases. The second part considers the agronomic management of the floodwater ecosystem. First, it summarizes the effects of crop intensification on floodwater ecology and the possible related effects on soil fertility. Then it reviews the cultural practices that take advantage of the agronomic potential of the floodwater ecosystem by 1) promoting photodependent biological N2 fixation by free-living and symbiotic cyanobacteria, 2) decreasing N losses due to NH3 volatilization, and 3) producing additional sources of proteins through the introduction of edible animals, especially fish. Finally, it considers strategies to alleviate the effects of floodwater inhabitants that are detrimental as rice grazers or as vectors of human diseases
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