抄録
印度型と日本型水稲の特性の相違を明らかにするため, Kaladumai・Dular (印度型) , 豊年早生・農林17号 (日本型) を供試し, 幼穂形成期の前・後における追肥が水稲の生育・収量におよぼす影響についてポット土耕法により本試験を行い次の点が明らかとなつた.
1.供試した4品種とも収量は追肥区より基肥区において高く, 穂数の確保が収量構成の第1要因となつた.これは分げつ盛期における多窒素条件下の茎数増に基因する.
2.日本型水稲の幼穂形成期後追肥は玄米千粒重を増大せしめるが, 印度型水稲における追肥は玄米千粒重に関与しない.
3.単位根重当りの根の活力は日本型水稲より印度型水稲において大きく, 糊熟期・収穫期の葉身における窒素含有率も日本型水稲に較べ印度型水稲が高かつた.
以上のことより, 印度型水稲は幼穂形成期前・後の追肥による稔実歩合・千粒重の増大は不可能であり, この原因については地上部に吸収された窒素の籾生産に対する効率が問題となり, 印度型水稲に対する生育後期の追肥は栄養生長を延長させる結果となること, さらに, 印度型品種は生育後期の追肥により根の活力は増大するが, 窒素同化のため, エネルギーの不足から可溶態窒素/全窒素の比率が高まり籾生産をかえつて阻害することが推測される.
In order to make clear the differences of the characteristics between Indica-type varietiesand Japonica-type varieties, by the pot soil culture method the experiment has been carried out about the influence of top dressing around the young panicle formation stage on the growth and yield of rice by using Kaladumai, Dular (Indica-type varieties) and Honen wase, Normn 17 (Japonica-type varieties) as sample, and has found the following results.
1. The grain yield per hill was higher in the ground fertilizer application than in top dressing treatment for all the four varieties, and the maintenance of the number of panicle became the primary factor of the yield components.
This was due to the increase of tiller under the condition of excessive amount of nitrogen at the time of vigorous, tillering stage.
2. The top dressing after the young panicle formation stage for Japonica type varieties increased the weight of 1000 kernel grains, but the top dressing for Indica-type varieties was no relationship with the weight of kernel grains.
3. The activity of root per unit root weight was greater in Indica-type varieties than Japonica-type varieties. The content of nitrogen inn the leaf blade after heading was also greater in Indica-type varieties than in Japonica-type varieties.
It was enterred from the above findings that the increase of 1000 grain weight and percentage of ripened grains resulting from the top dressing around the young panicle formation stage was impossible for Indica-type varieties. With respect to the causes of this fact, several reasons could be thought, but it is likely that this is due to the differences in the ability of assimilation, translocation and others in the body of rice and phase of growth.
