EXPLORATION OF EFFECTIVE IMPROVEMENT IN THE ACID SULFATE SOILS AND SELECTION OF INDICATOR WEEDY PLANTS FOR JUDGEMENT ON ACIDIFICATION PROCESS

酸性硫酸盐土是世界性的土壤问题之一。如果以适当的方法填海，我们预期可在不久的将来扩大土地面积，以供养更多增加的人口。本研究的目的是从土壤水分含量和生物活性的角度考察酸性硫酸盐土壤的酸化过程，并评价指示植物应用于改善土壤酸化的可能性。通过对土壤水分及其理化性质的调查，发现土壤的酸化是伴随着土壤干化的进程而进行的。然而，即使土壤的pH值下降与土壤水分的下降在紧接干燥后的时间段是平行的，土壤水分的特定范围，诸如表现出显著的低pH值的特定范围，在…的范围内出现在较晚的时间PH值下降较为显著，土壤酸化是由于硫酸根离子的增加，同时发现铁氧化细菌数量显著增加。在较高的土壤水分范围内，即使只观察到铁氧化细菌的存在，其数量也没有随着时间的推移而增加。而在较干燥的条件下，不适合饲喂铁氧化菌。由于在土壤初始盐浓度较低的情况下，氧化细菌的活性较高，所以上述现象在氧化过程中，即使黄铁矿被氧化的最后一步是相同的情况，土壤的初始盐浓度也越小。这些基础研究表明，在土壤在塑限条件下充分氧化后，施用石灰对酸性硫酸盐土壤的改良效果更好，这表明土壤在初始干燥阶段酸性发展剧烈。另一方面，在土壤干燥的初始阶段，即使是黄铁矿被氧化的最后一步，土壤的初始盐分浓度也越低，用石灰改良酸性硫酸盐土壤的效果就越好对指示植物的选择进行了研究，以明确几种杂草生长的pH适应条件，以及它们在酸性土壤中的适应范围。结果表明，芦荟、羊茅、猪笼草和黑麦草可以作为指示植物，特别是在高酸性土壤湿润条件下，而在旱地条件下，禾本科杂草如芒草、白茅草和结缕草可以作为指示植物。较少

The acid sulfate soils is one of the problem soils in the world. If they were to be reclaimed by appropriate methods, we expect to extend the acreage for feeding the more increased population in near future. The objectives of this research were to examine the acidification process of an acid sulfate soil from such a view point of soil water contents and biological activity, and evaluate the possibilities of utilization of indicator plants which suggest the improvement of the acidification of soils. The following are summaries of our results.From the investigation of soil water contents and their physical and chemical characteristics, it was found that acidification of soils proceeded under the progression of dryness of soils . Even if a decline in pH value of soil was parallel with those in soil water contents at the period of immediately after drying, however, the specific range of soil water contents such as showing a striking low pH value appeared at a later periodIn the range of a … More remarkable decline of pH, the acidification of soils result from the increase of surfuric ions, concurrently a remarkable increase in the number of iron-oxidizing bacteria was found . In more higher range of soil water contents, even if we observed only the exist of iron-oxidizing bacteria, an increase in the number of them had not occurred with the passage of time . While under more dryness conditions, it was not suitable conditions for feeding the iron-oxidizing bacteria.Since the activity of iro-oxidizing bacteria was higher under such circumstances that the, initial salt concentration of soil was lower, the above-mentioned phenomenon with oxidation process, even if final step when Pyrite was oxidized was the same situation, occurred the more remarkably the less the initial salt concentration of soil.Those fundamental studies suggested that it was more effective to improve the acid sulfate soil by the application of lime after soil was oxidized sufficiently under plastic limit conditions which indicated acute development of acidity at an initial dryness period.On the other hand, the research on selection of indicator plants was carried on to clarify the adapted pH conditions of several weeds for their growth, and their range of adaptation in acidic soils. As a result, Phragmites australis, Schoenoplectus validus, Hydrocotyle umbellala and H.verticillata seemed to be possible to use as an indicator plant, especailly in highly acidic soils under wet conditions, while the gramineous weeds such as Miscanthus sinensis, Imperata cylindrica and Zoysia japanica under upland conditions . Less