Effect of Nitrogen Top Dressing on Ripening of Japonica and Indica Rice

[摘要] Generally in indicas, compared with japonicas the carbohydrates concent in plant is less at heading time, number of spikelets per panicle is more, ripening period is short, therefore, competiton for absorbing carbohydrates among kernels on panicle is very severe and inferior kernels become sterile, abortive and opaque easily. By top dressiag in indicas carbohydrates content at heading stage decreases and number of spikelets per panicle, especially on secondry branches increases, then the competition among kernels becomes more severe causing the inferior kernels stop their growth and bdcome sterile, abortive and opaque kernels. More over grain weight of normal kernel is also decreased. In japonicas, carbohydrates content scarcely decreases and increase in number of flowers per panicle is small, which causes the ripening slightly deteriorate, and on the other hand the grain weight shows a slight increase. As a result in two varieties of japonica, grain yield per panicle is increased. Grain yield of Dular remains unchanged, where as, a slight decrease and rather decrease is obtained in case of Bluebonent and Te-Tep respectively. Karalath, which is thought a most unadaptable variety to heavy manuring decreases to 84%. Moreover, by heavy manuring, increase of panicles per plant is conslderable in japonicas, but it is small in indicas, so heavy manuring obviously causes increase of the yields in japo-nicas and scarcely increases rather decreases in indica varieties. In the light of these points it could be recommended that increase of yields can be obtained with the additional nitrogen fertilizer, when depending upon the nitrogen application the number of panicles per plant is increased and the flowers per panicle, particulary the flowers of secondary branches are kept almost constant. In varieties having such characteristics, the ripening does not deteriorate and high yields of good quality are expected. (Kinmaze and Towada) Besides this, with high nitrogen when panicle increases in size, branches in(:rease in number but the number of flowers on secondary branches does not increase or increase nominally the ripening is not severely worsened. This characteristic is also suitable for heavy manuring. This trend is observed in Bluebonnet.

[学科分类] 农业科学（综合）