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Abstract: The insufficient illumination effect during the grain—filling stage has been studied. For early rice, the insufficient illumination effect oceured about 5 times per ten years in Jiangsu Province, and for middle and late rice, about 4 to 5 times per ten years. When rice crops were suffering from the insufficient illumination effect, the ratio of earbohydrates to nitrogen in riee plants failed inbalance. The chlorophyll (a+b) content in rice leaves decreased, and the photosynthetic rate declined. As a result, both the fertility and grain weight of paddy dropped. However, the tolerance of insufficient illumination in different varieties, were different, Under insufficient illumination effect, the content of soluble sugar and starch in Indiea rice decreased more rapidly than that in Japonica rice. The increase of nitrogen content in the two varietal types difference was not significant. The reduction of chlorophyll content in flag leaves, the decrease of fruit and grain weight were considerably different among varieties. The insufficient illumination tolerance of rice plants was also effected obviously, by the nitrogen application rate and combination of fertilizers.

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