Studies on the Growth Phase of Direct Sown Rice Plant. : 1. Effects of nitrogen deficiency at the early growth stage on the growth phase of direct sown rice plant.

[摘要] In order to investigate the desirable growth phase of direct snwn rice plant, the experiment was undertaken to make clear the effects of nitrogen deficiency at the early growth stage on the growth phase of the plant by water culture method. The results obtained are as follows: 1. According to the period of nitrogen deficiency at the early growth stage of the plant becomes loner, the rate of leaf appearance was delavyed prominently, and the number of leaves on main stem was redubed, on the other hand, after having been supplied with nitrogen the rate of leaf appearance was more accelerated than before. Therefore, in cace the nitrogen deficient period was not too long, the plant was able to recover the number of lenves on the main stem. 2. So far as nitrogen nutrition is concerned, the coleoptile, the 1st leaf (next leaf of coleoptile) and the 2nd leaf blade grew up normally with nitrogen nutrition in the seed itself, and their growrths were not effected by nitrogen nutrition in nutrient solution, but the growth of the 2nd leaf sheath, the 3rd leaf (sheath and blade) and that follows were controlled remakably by nitrogen in nutrient solution. And in this experiment, the plant age which was able to grow up nomally with nitrogen in the seed was limited to the 2nd leaf stage of the young plant. 3. As the period of nitrogen deficiency at the early growth stage becomes longer, the weight of dry matter in top of the young plants was reduced remarkably, but after the plant have been supplied with nitrogen, the rate of increase of dry matter weight became larger. The dry natter weight of roots also showed the same tendency with that of the top, but the differences among the separate plots were not so remarkable as that of the top. 4. As the nitrogen deficiency period at the early growth stage becomes longer, the plant height became gradually shorter, but after having been supplied with nitrogen, the elongation of plant height was more accelerated than before, therefore, the plant height delayed in the early growth stage has recovered, and except -N plot, after the heading time the differences among the separate plots were not observed. 5. As the nitrogen deficiency period became longer, the number of stems decreased and the -N plot bore no tiller. 6. As to the heading time, differences among the separate plots were not oaserved, and the -N plot showed marked delay. 7. When the nitrogen deficiency period was short, there was practically no influence on the culm length, but when the period became too long, it acted to shorten the culm length. 8. The plots of nitrogen-deficiency-treatment generally bore longer ears than the control plot. 9. As the nitrogen deficiency period became longer, except the -N plot, the number of ears, weight of ears (yield), weight of straw and weight of roots (air-dried) decreased. However, the (weight of ear)/(weight of straw) ratio and the percentage of effective culms increased. As shown shown above, the nitrogen-deficiency-treatment at the early growth stage in dieect-sown rice plants gave a marked influence on the growing habit of young rice plants. However, after administering nitrogen, the rate of growth was increased and as long as the nitrogen deficiency period was not too long, the delayed of growth during the treatment peried could be recovered. Not only that but rather a reasonable degree of nitrogen-deficiency-treatment at the early growth period prevented the occurrence of over-growth which is one of the greatest defects of direct sown rice plants, and made it possible to raise the (weight ofe ars)/(weight of straw) ratio and the percentage of effective culms. It might be said that using such plants denser planting will be possible leading to an increased number of ears per unit area, and subsequently, to an increased yield.

[学科分类] 农业科学（综合）