Growth of Rice Plants in Late-Transplanting Culture with Special Reference to the Chemical Constituents of the Plant

[摘要] 1. It was reported before by the same authors, that in the northeastern districts of Japan, rice culture by late transplanting would be successfully practiced without any remarkable yield decreases provided the nursery plants be raised either by sparser seeding or by later seeding. In the present report the results of studies are given on the growth of rice plants grown by such particular methods, with special reference to the accumulation and translocation of carbohydrates as well as the behavior of inorganic elements such as N, K, P or Si in the plant. 2. The experimental plots of nursery were arranged as follows : (1) Seeding-density series - a) Standard culture plot, b) Sparse seeding - late transplanting plot, c) Dense seeding - late transplanting plot. (2) Nursery-period-length series - a) Standard culture plot, b) Sparse seeding - late transplanting plot, c) Late seeding - late transplanting plot. 3. With regard to the dry weight gained by the individual seedling plant at the end of the nursery period, the plots were found to be ranked as follows : (1) In the seeding-density series : - Sparse seeding - late transplanting plot > Dense seeding - late transplanting plot > Standard culture plot. (2) In the nursery-period-length series : - Sparse seeding-late transplanting plot < Late seeding - late transplanting plot < Standard culture plot. 4. C/N ratios in the plants at the time of transplanting were higher both in the sparse seeding plot and in the dense seeding plot than in the standard culture plot. 5. After transplanting, however, the progress of accumulation and translocation of starch, sugars, total carbohydrates or nitrogen compounds in the plants were found practically not different among them raised from the three plots of the nursery-period-length series. Translocation of accumulated substances to developing ears was assumed to have taken place smoothly in every plant from all the plots. The fact shown in the previous report, that, when seeded sparsely and late in the nursery, rice plants, though may be transplanted late, can yield nearly as well as those of standard culture, might be explained by such behaviors of the substances in the plants. 6. When the densely sown seedlings were transplanted late, both the tillering and heading delayed, and consequently the translocation of starch into the ears was retarded, resulting in poorer yields of crop. 7. Generally in late transplanting culture, the nitrogen content of plants increased more rapidly during the period of about 10-20 days after transplanting. As the germs of blast disease parasites prevail usually at that time, larger attention must be paid for control of the disease. 8. It is suggested that, for late transplanting culture of rice in those districts, especially early ripening, highly productive and blast resistant varieties should be used, and moreover, sufficient cares in nursery management and other cultural practices are desirable, even when sparse-sowing or late-sowing methods are adopted.

[学科分类] 农业科学（综合）