Physiological studies on the characters of rice seedlings as affected by the conditions of seed-bed period : preliminary

Abstract

(1) Adaptability of rice seedling raised in various nursery conditions to the degrees of nitrogen fertility of the paddy field was studied. The kind of nitrogen fertilizer management of the field to which the seedlings of various makings were transplanted and grown up to maturity were AB (N, basic and top-dressed), Ab (N, basic only). aB (N, top-dressed only) and ab(N, no applicaeion). (2) The seedling grown up sparsely in the nursery (I). was large when transplanted, containing more total nitroten (N) and carbohydate (C) as compairing with the small seedling grown on the densely sown bed (III). The plant from such large seedling could absorb large amount of N in its early stage of growth, but the increment of N percentage in that stage proceeded more slowly in the plant than in plant from the sman seedling above mention. At the late stage of the vegetative growth, the plant from large seedling showed, after all, a higher percentage of N content than the plant from the small seedling, and the former shoot the ear earlier than the latter. The yield records of two years experiments showed that the large seedling resulted frorn sparsely sowing was more suitable to the basic-dressed field than the top-drssed one, while, the small seedling produced by thick sowing grew up better when the field was top-dressed. (3) The seedling of early sown and left over time in the nursery ('matured seedling') (lV) was, when transplanted, rather deficient in N as compared with C content, while the seedling of lately sown and kept at nursery for comparatively short period ('young seedling') (VI) was rich in N, comparing with C. The matured seedling maintained its lower N percentage for a time after transplanting, aspecially so in the field receiving no basic application of N. In the later stage of growth, the N absorbing power of such plant seemed to be smaller than the plant from young seedling. In warm year (1946), or on N rich fields, the N absorbed by the matured seedling showed higher efficiency for grain production than that absorbed by the young seedling. In cool year(1945), or on N deficient fields, however, the young seedling, absorbing larger arnount of N, showed higher efficiency of N than the matured seedling in producing grain. (4) The seedling grown up under limited light intensity (VIII) had smaller amount of N and C, and its C-N ratio was lower than that found in the seedling grown under full light intensity (VII). In 1946 the shaded seedling behaved in the field more like the small seedling, and in 1945 rather like the young seedling. The seedling raised on non-irrigated nursery (IX) had larger amount of N and C, and its C-N ratio was lower at the transplanting stage. Moreover, after transplanting N content in unit dry matter of such plant increased more distinctly that of the plant nursed on full irrigated bed (VII). In 1946 the non-irrigated seedling behaved chiefly as the large seedling, and in 1945 it behaved as the young seedling. (5) The authers conclude that the amount and percentages of N and C, and the ratio of the both elements at the transplanting stage are very important seedling characteristics affecting the suitability of the seedling to a certain condition of soil fertility or the N fertilizing management. more total nitroten (N) and carbohydate (C) as compairing with the small seedling grown on the densely sown bed (III). The plant from such large seedling could absorb large amount of N in its early stage of growth, but the increment of N percentage in that stage proceeded more slowly in the plant than in plant from the sman seedling above mention. At the late stage of the vegetative growth, the plant from large seedling showed, after all, a higher percentage of N content than the plant from the small seedling, and the former shoot the ear earlier than the latter. The yield records of two years experiments showed that the large seedling resulted frorn sparsely sowing was more suitable to the basic-dressed field than