Studies of production ecology on the rice plant population grown under low pesticide circumstances

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All over Japan had good weather. much sun-shine and high temperature, during rice growing season. So that rice headed 7-10 days earlier than as usual. Research meetings were held twice, in Yamagata University in July 1994, and in the University of Tokyo in February 1995. Our experimental results showed nearly the same tendency about grain yield against planting density except the university rice field in which rice plant were suffered severe cool temperature damages.1)There was two groups against the planting density and grain yield. In one group, low density plants produced nearly the same level grain yield against the local conventional plant density. On the other hand, low density plants got less yield than the conventional one. These responses occurred to fifty and fifty.2)Fertilizer response to grain yield was consistent through three years. Nitrogen fertilizer showed conspicuous effect to raise grain yield. However, it increased pests and disease damages with increase its application rate. In, reverse, low nitrogen application helped to raise healthy plants, while it reduced grain yield.3)Low pests and disease damage and higher level yield were expected in the combination of lower planting density and moderate nitrogen level of the local conventional condition. In that case, It seems that the condition of relative fertile soil and sufficient temperature for ripening stage were required.