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

日本各地都有好天气。在水稻生长季节，阳光充足，温度高。因此，水稻抽穗比平常早7-10天。1994年7月在山形大学和1995年2月在东京大学举行了两次研究会议。结果表明，除低温冷害严重的大学稻田外，水稻产量与种植密度的变化趋势基本一致。1）种植密度与水稻产量的关系存在两组效应。在一个组中，低密度植株产生与当地常规植株密度几乎相同水平的籽粒产量。另一方面，低密度植株的产量低于常规植株。这些反应发生在50和50。2）肥料对产量的反应在三年中是一致的。氮肥对提高粮食产量效果显著。但随着施用量的增加，病虫害发生率也随之增加。在当地常规种植条件下，低密度和适度施氮水平的组合，可获得较低的病虫害危害和较高的产量。在这种情况下，似乎需要相对肥沃的土壤和成熟期足够的温度条件。

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.