Abstract
For studying the microbiological and chemical properties of paddy soil, samples were collected at a relatively short periods namely 2 weeks from a lysimeter water-logged and cultivated with rice, for the microbiological and chemical analyses. The results obtained were as follows: 1. Organic matter and total nitrogen fluctuated throughout the experimental period. 2. NH₃-N showed a marked increase as a result of water logging-and application of ammonium sulphate, followed by a gradual decrease due to plant uptake, leaching and denitrification process. 3. NO₃-N on the other hand, decreased early after water-logging. This decrease was however more pronounced than that recorded for NH₃-N, denoting that the latter form of soluble nitrogen was held more tightly in the clay minerals of soil. 4. Drying of the soil increased the NH₃-N and NO₃-N, due to aeration that favored ammonification and nitrification processes. 5. Soluble phosphorus increased early after water-logging, followed by a gradual decrease thereafter due to plant uptake, leaching and fixation in the soil. 6. T. S. S. decreased as a result of leaching. 7. Soil pH slightly increased as a result of water-logging, due to the activities of nitrate and sulphate reducing organisms. 8. Total microbial flora and actinomycetes decreased as a result of waterlogging. Azotobacter, nitrifiers, and cellulose decomposers increased early after water-logging. Later, their counts showed a marked decrease as a result of oxygen depletion, and exhaustion of nutrients and sources of energy. 9. Spore-formers, Clostridia, denitrifiers, and sulphate reducers significantly increased after water-logging. This indicates the activities of the latter organisms in the reduction process in paddy soils. 10. Drying of the soil disturbed the microbial equilibrium, being in favor of the aerobic organisms. Total microflora, Actinomycetes, Azotobacter, nitrifiers, and cellulose-decomposers showed a marked increase as a result of aeration and presence of organic matter as plant debris. On the other hand, Clostridia, denitrifiers and sulphate reducers showed a slight decrease.