Studies on Competition between Upland Crops and Weeds : V. The period for weed-free maintenance

[摘要] The experiment on competition between upland crops and weeds was conducted with four upland crops which were typical in the Kanto plain. And from aspect of the effects of different periods of weed-free maintenance on the crop yields, adequacy of the period for weed-free maintenance hypothesized in the previous report was estimated. 1. In upland rice and soybean cropping plots, plant length of large crab-grass (Digitaria adscendence Henr.) at the plots of 0 and 30 days weed-free maintenance extended up to the upper part of crop canopies which maintained the relative light intensity under 10%. On the other hand, that at the plots of 47 and 58 days weed-free maintenance was limited to the lower part of crop canopies. In peanut cropping plots, even that at the plot of 58 days weed-free maintenance extended up to the upper part of crop canopies. As the plant height of corn was high, even that at the plot of 0 day weed-free maintenance was kept to the lower part of crop canopies. 2. The later the time of competition with weeds started, the smaller the ratio of weed weight to total community weight became. The ratio of weed weight to total community weight in corn was the smallest of all crops, that is, was under 25% at the plot of 0 day weed-free maintenance, and was under 5% at the plots of 30 and 47 days weed-free maintenance. The ratio of weed weight to total community weight in upland rice and soybean was large at the plots of 0 and 30 days weed-free maintenance, but was small at the plots of 47 and 58 days weed-free maintenance. That of peanut was the largest, and was over 30% even at the plot of 58 days weed-free maintenance at harvesting. The amount of weeds at harvesting were little in corn, medium in upland rice and soybean, and much in peanut. And those showed approximately similar results to the ratio of weed weight to total community weight. Namely, the smaller the weed weight to total community weight was, the less the amounts of weeds at harvesting became. 3. Effects of weeds on crop yields were reflected in results of competition between crops and weeds. The yields of upland rice and soybean reduced at the plots of 0 and 30 days weed-free maintenance, as growth of weeds was not diminished greatly by crop canopies. But reduction of yields did not occur at the plots of 47 and 58 days weed-free maintenance, as growth of weeds was diminished greatly by crop canopies. The yields of peanut reduced at all plots of competition with weeds, as weeds grew rampant. In corn, significant reduction of weights of ears did not occur even at the plot of 0 day weed-free maintenance, but weights of stems and leaves reduced. Crop yield reduction due to weeds did not occur at the plots of 30 and 47 days of weed-free maintenance. 4. From above results, it was clear that hypothesis about the period for weed-free maintenance after seeding required to escape crop yield reduction due to weeds had high adequacy.

[学科分类] 农业科学（综合）