These studies were carried out for the elucidation of liming effect on the growth of rice seedlings and the chemical characteristics of an acid sulphate paddy that shows not only extremely high acidity of soil but also poor growth of rice plants, consequently low yield. Thus the liming effect on the changes of acidity, oxidation-reduction potential, and the contents of iron, aluminium, sulphate, and phosphorus fractions in the soil was investigated under the waterlogging and drying condition. The reclaimable or inhibitory effect of phosphorus, iron and aluminium on the growth of rice seedlings was also investigated under liming.
The results are summarized as follows:
1. After liming, the pH of the acid sulphate subsoil decreased again on drying.
2. The oxidation-reduction potential reached a minimum after 5 days of flooding and greatly decreased on liming but increased after drying.
3. The contents of ferrous iron soluble in water-and Morgan´s solution reached a maximum after 15 days of flooding and only the content of water soluble ferrous iron was greatiy decreased.
4. The content of aluminium soluble in water-and Morgan´s solution decreased by flooding and liming, and showed a tendency to increase on drying.
5. In the limed acid sulphate soil, the content of water soluble calcium showed a highly significant negative correlation with the content of sulphate and liming decreased sulphate content in the soil.
6. The contents of total phosphorus was 496.3 ppm in the acid sulphate topsoil and 387.5 ppm in the subsoil. The content of each phosphorus fraction was in the order of Fe-P$gt;Occ. Fe-P$gt;Ca-P$gt;Occ. Al-P$gt;Al-P and Fe-P content in the soil was the highest fraction among them.
7. Lime application increased greatly Ca-P and Al-P, and Occ. Fe-P and Occ. Al-P only slightly, but decreased Fe-P differently in each soil.
8. Effect of phosphorus on the dry matter yield of rice seedlings was great. The optimum amount of phosphorus to produce maximum dry matter yield of rice seedlings appeared to be 6.8% of maximum absorption (absorption coefficient) without liming and 10.0% with liming.
9. In rice seedlings liming increased the content and uptake of calcium and silica but decreased those of iron and aluminium. Phosphorus application increased the content and uptake of phosphorus and decreased iron while the application of iron and aluminium increased their contents and uptake but decreased those of phosphorus.
10. Liming greatly alleviated such toxicity of iron and aluminium.
11. When phosphorus was applied, the dry matter yield of rice seedlings showed highly significant positive correlations with uptake of phosphorus, calcium and silica each. When iron and aluminium were applied, dry matter yields indicated significant positive correlations with the contents or uptake of calcium and silica each, but significant negative correlations with the content or uptake of iron and aluminium.
12. Under the application of phosphorus and lime, dry matter yields showed significant positive correlations with pH and Morgan´s extractable calcium each of the soil samples after harvest. Under the application of lime, iron and aluminium, dry matter yields showed significant positive correlations with pH, calcium and silica each, but negative correlations with iron and aluminium contents each of the soil samples after harvest.
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