SUGIO Tsuyoshi OKAYAMA UNIVERSITY,FACULTY OF AGRICULTURE,PROFESSOR, 農学部, 教授 (20033269)
OKI Yoko OKAYAMA UNIVERSITY,FACULTY OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY,ASSOCIATE PRO, 環境理工学部, 助教授 (30127550)
|Budget Amount *help
¥7,600,000 (Direct Cost : ¥7,600,000)
Fiscal Year 1998 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1997 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1996 : ¥6,100,000 (Direct Cost : ¥6,100,000)
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 period
In the range of a
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