表土の深淺が水稻の成育に及ぼす影響
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概要
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1. In containers, 25 cm. in diameter and 1 m. in depth, after packing sandy soil to the suitable depth according to that of the surface layer and a clay layer 10 cm. thick upon it, loam from an unfertilized rice field was layed as the surface layer, whose thickness was 10, 30 and 60 cm. respectively. Fertilizers were applied at the following rates by mixing them with the whole surface soil, before packing it in the containers: (snip) Growing rice plants in these containers, the effects of the depth of surface soil and the amount of fertilizers on the plant growth were studied. The results are shown in TABLE 1 on p. 163. 2. As the surface layer was thicker, not only the roots developed more deeply, but the greater parts of them functioned in the fertilized surface layer (Fig. 1.). This condition in the root development appeared to affect the growth of the top as stated bellow. 3. The thinner the surface layer was, the more the plant tillered. This may be attributed to the following fact. The thinner the surface layer was, the more fertilizers were applied per unit mass of soil in the shallow layer, and consequently the better the plant was nourished in its tillering stage, as the roots developed mainly in the shallow layer in this early stage. 4. If the surface soil was too thin, however, as the plant grew into its shooting stage, the plant using up fertilizers and the roots developing into the unfertilized layers, the nutrition became insufficient and the plant could not form large number of spikelets notwithstanding its many tillers. But, by this period the plant in the deepest surface soil could not yet develop its roots in the thick surface layer to such an extent to utilize the fertilizers in it fully, and could not have so many spikelets as to cancel its smallness in the number of tillers. Thus, the plant in the surface layer of the medium depth had always the largest number of spikelets, being followed by that in the thickest or in the thinnest layer, according to the small or Iarge amount of fertilizers applied. 5. When the plant grew into its ripening stage, the nutritive condition of the plant was better with the thicker surface soil layer, and hence the plant in the thickest surface soil showed the best results in the ratio of fertility (the ratio between the number of ripe grains and the total number of spikelets), in the weight of moo ripe grains, in their yield and in their nitrogen content. And, with the thinner surface layer the magnitudes of these factors decreased. 6. The effect of the amount of fertilizers applied on the various factors determining the yield mentioned above appeared to be more conspicuous when the surface layer was thinner. 7. From the above it may be concluded that the yield of unhulled grains is the resultant of the number of ears, the number of spikelets per ear, the ratio of fertility, and the weight of individual grains, which are determined by the nutritive contition of the plant when these processes are performed. In the case of this experiment, the nutritive condition of the plant at its various growth stage appeared to be determined by the relation between the root development and the soil conditions. It is another problem, however, whether the results here obtained can generally be adapted to cases under field conditions, because the conditions in the field would be more complex compared with those under which this experiment was carried out. 8. Among farmers, in order to obtain a big yield, it is often practiced to apply phosphoric acid abundantly with large amount of nitrogen in the field of very thick surface soil. This experiment was partly planned to study on this problem. The effect of such large amount of phosphoric acid, however, could scarcely be detected.1. 直徑 25cm, 深さ1m. の亞鉛引鐵板製の圓筒に底土として砂土を所定の表土の厚さに應じて適當の深さに填め, 其の上に約 10cm. の厚さの固い粘土層を作り, 更に其の上に夫々 10, 30 及び 60cm. の深さに水田の耕土を填充した。耕土には填充に先ち全部基肥として種々の量の肥料を―主として窒素の―よく混和して施した。之に水稻を栽培して表土の深淺及び施肥量の植物の成育に及ぼす影響を觀察した。2. 地上部の收穫後根の發育状態を觀察した結果に據れば, 表土の深きに從ひ根の全長は長く, 且其の表土層内にある割合は大に, 淺きに從ひ之と正反對であつた。3. 表土の最も薄い區に於ては, 初期の成育は最も可良にして, 最も多く分蘖したが, 程なく其の榮養は蓑へて, 大なる穗を形成し得ず, 稔實歩合は低く, 葉は早く黄變して成熟は促進され, 種實の充實不良にして輕く其の含窒量は最も小に, 而して收量は最も少なかつた。4. 表土 30cm. の區に於ては, 前者に比し分蘖は稍々後れたとはいへ, 最後の穗數には大差なく, 穗亦大にして一株の籾撒は最も多く, 藁の政量は最も大であつたが, 成熟期に入つて榮養は衰へ, 稔實歩合は低く, 種實の充實も亦良好でなかつた。而して玄米の收量及び其の含窒素量は他の兩區の中間であつた。5. 表土の最も厚い圍では, 初期の成育は劣り, 分蘖は最も少く, 穗も其の割合に大なる能はずして. 一株の籾數は 30cm. の區に劣つたのみならず, 施肥量多き場合には 10cm. の區にすら劣つたが, 成熟期に入るも其の榮養は蓑へずして稔實歩合は高く, 葉は長く緑色を呈して成熟は後れたが, 之が爲種實の充實は最も可良にして, 其の含窒量は最も高く, 終に最大の立米收量を擧げた。6. 施肥量の増加による増收率は表土の淺きに從つて著しかつた。
- 九州帝國大學農學部の論文
- 1932-10-00
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