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范围内存在问题的土壤之一。如果采用适当的方法进行开垦，我们期望在不久的将来扩大耕地面积，以养活更多增加的人口。本研究旨在从土壤含水量和生物活性的角度考察酸性硫酸盐土壤的酸化过程，并评价利用指示植物改善土壤酸化的可能性。以下是我们研究结果的摘要。通过对土壤含水量及其理化特征的调查，发现土壤的酸化是在土壤干燥的过程中进行的。即使土壤pH值的下降与土壤含水量的下降是平行的，但土壤含水量的下降也出现在较晚的时期，例如pH值显着降低，在一个范围内，更显著的pH下降是由于表面离子的增加导致土壤酸化，同时发现铁氧化细菌的数量显著增加。在较高的土壤含水量范围内，即使只观察到铁氧化菌的存在，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，则不适合铁氧化菌的饲养。由于在土壤初始盐浓度较低的情况下，铁氧化细菌的活性较高，因此在氧化过程中，即使最后一步黄铁矿氧化的情况相同，土壤初始盐浓度越低，上述现象发生的越显著。这些基础研究表明，在塑性极限条件下，土壤充分氧化后，施用石灰对酸性硫酸盐土的改良效果更好，这表明在初始干燥期酸性急剧发展。另一方面，对指示植物的选择进行了研究，明确了几种杂草在酸性土壤中生长的适应pH条件和适应范围。结果表明，芦苇（Phragmites australis）、白穗草（Schoenoplectus validus）、伞形水子叶（Hydrocotyle umellala）和黄斑草（h.w verticillata）在高酸性土壤中具有指示植物的潜力，而禾草（禾草）、白茅（Imperata ica）和结缕草（Zoysia japanica）在旱地条件下具有指示植物的潜力。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