Studies on the Varietal Adaptability for Heavy Manuring in Rice : 2. Effect of silica upon the adaptability of the rice plant for heavy manuring in relation to photosynthesis

It has been considered that silica is one of the factors which influence the adaptability of rice plant for heavy manuring. In this paper, the influence of silica on the adaptability for heavy manuring of rice plant was investigated in particular with regard to photosynthesis. Experiment was carried out using aggregate plants which were solution-cultured under four combinations of nitrogen and silica supply. Results obtained were as follows: 1. At heading stage, high supply of silica increased the leaf area and the photosynthetic capacity of the plants as a whole, and decreased their respiration (Table 3, 4 and Fig. 2). Such an effect of silica was greater at high nitrogen level than low level. 2. High silica supply also brought about slight decrease of photosynthetic activity on unit leaf area (Table 3). However, the ratio of unit photosynthesis to respiration was greater in high silica plot than in lower one, because of the greater decrease of unit respiration rate in the former plot (Table 3). 3. The plants supplied with sufficient silica showed an improvement in their form of assimilation system as to be able to receive light with higher efficiency than the plants of less silica supply (Table 4). The improvement may, it was found, mainly in that the leaves attached to the stem at more acute angle and that the leaves themselves were less curved and thick (Table 5). 4. From the above results it may be concluded that, by the application of sufficient silica, the low efficiency, in dry matter production, which is invitable with those plants grown too much luxuriantly as an aggregate under heavy nitrogen supply, can be improved to some extent and, as a result, the overall adaptability of the plants for heavy manuring can be increased.