Studies on the photosynthesis and dry matter production of rice plants. I. Varietal differences in photosynthetic activity induced by nitrogen top-dressing

An investigation was made concerning the influence of nitrogen top-dressing at a later stage of growth on the leaf photosynthetic activity in some newly improved rice varieties of Korea obtained by indica-japonica crossing. The results are as follows: 1. Considerable varietal differences were observed in the apparent photosynthetic activity on leaf area basis determined by oxygen evolution. The Milyang lineage and the Iri lineage showed the highest activity, the other varieties being in the order of Suweon lineage, the japonica (Somewake), and the indica (T-136). The early-maturing varieties showed a tendency to have somewhat higher photosynthetic activity than the later-maturing varieties. 2. Nitrogen content on leaf area basis was lower in the indica-japonica hybrid varieties than in the japonica variety. 3. The nitrogen top-dressing promoted photosynthetic activity in all the varieties, but the degree of response differed from variety to variety. 4. Photosynthetic activity on leaf nitrogen basis also showed varietal differences, regardless of the nitrogen top-dressing. 5. Furthermore, the photosynthesis-promoting effect of increased leaf nitrogen content duc to top-dressing was generally higher in the indica-japonica hybrid varieties than in the Japonica or the indica. 6. By nitrogen top-dressing both NAR and leaf area development were enhanced, leading to increased CGR. This trend was especially clear in the indica-japonica hybrid varicties.