Studies on Weed Competition and Effects on Rice:Competitive Effects of Barnyardgrass at Successive Stages of Rice
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In the previous paper, the competitive effects of barnyardgrass on the growth, yield, and some eco-physiological characters of rice were explained, and it had been considered that the effects might be different according to successive stages of rice. Therefore, over a period of three years, 1966, 1967, and 1968, the competitive effects of barnyardgrass at successive stages of rice have been experimentally confirmed, making to some extent different growing conditions of rice and barnyardgrass every years. The results are summarized as follows:1. Summarizing the results of three years, two periods when rice was adversely and dramatically affected due to existence of baryardgrass, were found. The first period is around the maximum tillering stages of late July to early August, and another is ripening stages after heading from middle of September to early October.2. Competition with barnyardgrass in the first period principally provided the decrease in panicle number resulting in the reduction of rough rice yield, particularly its degree was found highly under fertilized conditions which were made laying importance on basal application.3. That in the second period gave the reduction of kernel weight as well as the decrease in the number of perfect kernels to cause the loss of yield, and was encouraged by fine climatic conditions with abundant sunlight besides fertilized conditions that is effective at later stages of rice.4. There was an intermittent period receiving less competitive effects between the first and second ones above-mentioned, in which disappearing of non-effective tillers and the differentiation of panicles occur.5. The productive structure of rice plants degenerated dramatically by competition with barnyardgrass, particularly the degeneration was markedly found in lowering the proportion of leafblade which is a main assimilative part.6. The root system of rice coexisted with barnyardgrass was investigated comparing with that of weed-free rice. As a result, It was observed that spreading of the rice roots into the tillaged layer of soil is in a trend of inhibiting.
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