ミズアオイとコナギの生育並びに種子生産に対する播種時期, 遮光および施肥量の影響  [in Japanese] Effects of Time of Sowing, Shading and Compound Fertilizer Application on Growth and Seed Production of Monochoria korsakowii Regel et Maack and M. vaginalis (Burm. f.) Kunth  [in Japanese]

ミズアオイとコナギの生育並びに種子生産に対する播種時期, 遮光および施肥量などの影響について検討し, 次のことを明らかにした。1) 草丈はいずれの播種時期においてもミズアオイがコナギよりも高かった。主茎葉数は5月までの播種期においては, ミズアオイがコナギよりも多かったが, 6月以降の播種期においてはコナギの方が多かった。2) 種子生産量は, 両草種ともに5, 6月播種で大きい値を示した。3) 各器官への乾物分配率を4月と8月播種で比較すると, 前者では生殖器官への分配が生育後期に集中したのに対して, 後者では, 生育前期より生殖器官への分配が認められた。4) 草丈は両草種ともに無遮光条件では無施肥区が最も低かったが, 遮光が強化されるに伴い, 逆に無施肥区で草丈が最も高くなり, 倍量施肥区が最も低く推移し, 標準施肥区は両者の中間の草丈を示した。5) 種子生産量は無遮光条件では施肥量の増加に伴い, 明らかに多くなった。しかし, 遮光処理区では両草種ともに播種後90日に25%遮光開始の倍量施肥区で種子生産量が最大となった。

Effects of time of sowing, shading and compound fertilizer application on the growth and seed production of Monochoria korsakowii and M. vaginalis were investigated in Kyoto, Japan. The results are summarized as follows. When sown until May, M. korsakowii displayed a larger number of leaves on the main stem than M. vaginalis, while when sown from June, the results were opposite (Table 1). This phenomenon was attributed to the quicker growth of M. korsakowii under low temperature conditions in spring than that of M. vaginalis. In the case of M. vaginalis, the amount of seeds which was larger in the weeds sown in May and June than in those sown in other months, tended to depend on the top dry weight. In the case of M. korsakowii, though the weeds sown in May and June also showed an amount of seeds as large as that of M. vaginalis, the top dry weight of the weeds sown in March and April was larger than in other months (Fig. 1 and Table 2). In both species, partition of dry matter production to reproductive organs started at the late growth stage in the April sowing, while at the early stage in the August sowing (Fig. 2). Both species exhibited maximum plant height under shading of 25% relative intensity, while seed production per plant increased when the dose of compound fertilizer applied increased. The results obtained suggested that the weed became adapted to shading and soil fertilizer. In a natural population where rice was present, both species grew better under shading by the canopy of rice and produced a larger number of seeds in soil amended with compound fertilizer. Without shading, the amount of seeds increased considerably with the increase of the fertilizer level. Under the shading conditions, the amount of seeds of both species was largest when 25% shading was applied 90 days after sowing. On the other hand, the amount of seeds decreased with the increase of the shading level and when the onset of shading was advanced (Tables 3 and 4).