Growth and Seed Production of Scirpus juncoides Roxb. subsp. juncoides in Paddy Fields.
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概要
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Field experiments were carried out to investigate the growth and seed production of Scirpus juncoides Roxb. subsp. juncoides in paddy fields transplanted with young rice seedlings. The results obtained are as follows;1. In a bare paddy field without rice plants, about 9, 700 seeds per plant were produced when the Scirpus seedlings emerged on June 18. More than 3, 000 seeds per plant were produced by the plants which emerged before July 16, although the seed number was smaller when the seedlings emerged later.2. In a paddy field with transplanted rice, the number of weed seeds per plant was about 100 when the seedlings emerged immediately after rice transplanting on June 18. Heading of S. juncoides was not observed when the seedlings emerged after July 16, thirty-two days after rice transplanting. Most of the seeds were not mature when the seedlings emerged eighteen days after rice transplanting, because the duration of the grain filling period of S. juncoides was insufficient for seed maturation before rice harvesting time. Accordingly it was shown that the plants produced few mature seeds when seedlings emerged more than one month after rice transplanting.3. The plants emerging from over-wintering buds, which grew more rapidly in the early stage of rice cultivation than those from seeds, produced 1, 500 seeds per plant in the paddy field with rice plants, and 17, 000 seeds per plant in the bare paddy field.4. The number of seeds of S. juncoides per plant was not different among emergence densities of more than 500 plants per sq. meter. About 65, 000 seeds per sq. meter were scattered on the paddy soil surface at the density of 1, 000 plants per sq. meter. However fewer seeds were produced when the plant emergence density was higher, because the plant density at the rice harvesting time decreased due to competitive pressure.5. The number of seeds per plant was highly correlated with the foliage air-dry weight, although the values of latter parameter varied with the emergence time and plant density of S. juncoides and the growing conditions in paddy fields.
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