| In this dissertation, we researched the exploration and elimination of the ferrous and reducing sulfur toxicity in waterlogged paddy soil by greenhouse pots and soil culture experiments. Information provided in this work may contribute to a better understanding of the rice physiological indices, soil microbial activities and effectiveness of slag and fermented rice husk in the interactive system of soil-rice-ferrous/reducing sulfur and microbe in waterlogged paddy field. Main original conclusions are shown as follows.1. The effect of exogenous ferrous (Fe2+) treatment on the rice physiological indices, soil microbial activities and its bioecological characters at seedling and tillering stage in the interactive system of soil-rice-ferrous and microbe were studied by a greenhouse pot experiment which simulated the ferrous toxicity in waterlogged paddy soil. Ferrous was applied at six different levels in one paddy soil, namely0,100,200,400,800and1600mg/kg. The results showed that the addition of exogenous Fe2+gradually inhibited the growth of rice and decreased soil microbial activities while the background Fe2+concentration of the normal tested paddy soil was207.77mg/kg. The plant height and dry matter accumulation of rice decreased sharply when exogenous Fe2+concentration exceeded100mg/kg. However, SPAD value of chlorophyll content in rice leaf, proline accumulation and activities of antioxidant enzyme systems increased significantly. It suggested that exogenous Fe2+of100mg/kg was the critical concentration under tested condition to poison rice growth. Meanwhile,soil microbial activities declined rapidly and then steadily with the increase of the concentration of exogenous Fe2+. The turning point of decreasing soil microbial activities can be presumed as100mg/kg of exogenous Fe2+concentration by analyzing its toxicant concentration that inhibits a microbe-mediated ecological process by50%(EC50). Soil microbial activities and rice growth in the system of soil-rice-ferrous and microbe were significantly associated and synchronously affected by the ferrous in tested soil. Overall, exogenous Fe2+of100mg/kg was the critical concentration to inhibite rice growth and decrease soil microbial activities in tested soil. Therefore, based on the above results, the concentration of ferrous toxicity in tested paddy soil can be presumed as about300mg/kg which included the background. Some reasonable agronomic measures should be taken to control the negative effects once the concentration of ferrous iron overstep such concentration in the test paddy soil.2. The effect of exogenous reducing sulfur (S2-) treatment on the rice physiological indices, soil microbial activities and its bioecological characters at seedling and tillering stage in the interactive system of soil-rice-reducing sulfur and microbe were studied by a greenhouse pot experiment which simulated the reducing sulfur toxicity in waterlogged paddy soil. Reducing sulfur was applied at seven different levels in one paddy soil, namely0,10,50,100,300,600and1200mg/kg. The results showed that the addition of exogenous S2-gradually inhibited the growth of rice and decreased soil microbial activities while the background S2-concentration of the normal tested paddy soil was12.08mg/kg. The plant height and dry matter accumulation of rice decreased sharply when exogenous S " concentration exceeded50mg/kg. However, SPAD value of chlorophyll content in rice leaf, proline accumulation and activities of antioxidant enzyme systems increased significantly. It suggested that exogenous S2-of50mg/kg was the critical concentration under tested condition to poison rice growth. Meanwhile,soil microbial activities declined rapidly with the increase of the concentration of exogenous S2". The turning point of decreasing soil microbial activities can be presumed as40mg/kg of soil S2-concentration by analyzing its toxicant concentration that inhibits a microbe-mediated ecological process by50%(EC50). Soil microbial activities and rice growth in the system of soil-rice-reducing sulfur and microbe were significantly associated and synchronously affected by the reducing sulfur in tested soil. Overall, soil S2" of40mg/kg was the critical concentration to inhibite rice growth and decrease soil microbial activities in tested soil. Therefore, based on the above results, the concentration of reducing sulfur toxicity in tested paddy soil can be presumed as about40mg/kg which included the background. Some reasonable agronomic measures should be taken to control the negative effects once the concentration of reducing sulfur overstep such concentration in the test paddy soil.3. The sorption of ferrous sulfate and reduced sulfur by slag and fermented rice husk was studied by using batch technique. The effects of solution concentration, pH, the temperature and ionic strength on the sorption were investigated. Through the desorption experiment, we further validated their adsorption stability. The results suggest that the adsorption kinetics of ferrous sulfate and reduced sulfur by steel slag and rice husk follow the Elovich kinetics. The adsortion process is endothermic process because high temperature is benefical to their adsorption; they have greater pH adaptability; the adsorption of Fe2+is major in inner sphere complexation, the adsorption of S2" is major in outer complexation. The adsorption rates are all very high, and the desorption rates are low in different experiment conditions, which shows that the adsorption stability is superior. On the whole, slag and fermented rice husk are good adsorption materials of Fe2+and S2-.4. The effect of exogenous slag treatment on the soil microbial activities and its bioecological characters, the value of ferrous iron and reducing sulfur, the feature of nutrient at different periods in the interactive system of soil-ferrous/reducing sulfur and microbe were studied by a soil culture experiment which simulated the ferrous/reducing sulfur toxicity in waterlogged paddy soil. Slag was applied at six different levels in one paddy soil, namely0,10,20,40,80and100g/kg. The results showed that the addition of exogenous slag gradually inhibited the the value of ferrous iron and reducing sulfur.However, soil microbial activities, the value of soil pH and nutrient increased significantly. Overall, exogenous slag of40g/kg was the suitable concentration to improve the tested soil, some reasonable agronomic measures should be taken to enhance its improvement effect.5. The effect of exogenous fermented rice husk treatment on the soil microbial activities and its bioecological characters, the value of ferrous iron and reducing sulfur, the feature of nutrient at different periods in the interactive system of soil-ferrous/reducing sulfur and microbe were studied by a soil culture experiment which simulated the ferrous/reducing sulfur toxicity in waterlogged paddy soil. Fermented rice husk was applied at five different levels in one paddy soil, namely0,10,20,40, and80g/kg. The results showed that the addition of exogenous fermented rice husk gradually inhibited the the value of ferrous iron and reducing sulfur.However, soil microbial activities, the value of soil pH and nutrient increased significantly. Overall, exogenous fermented rice husk of20g/kg was the suitable concentration to improve the tested soil, some reasonable agronomic measures should be taken to enhance its improvement effect. |
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