Studies on the Effects of Soil Physical Conditions on the Growth and Yield of Crop Plants : VII. Effects of soil air composition and soil bulk density and their interaction on the growth of sweet potato

[摘要] The authors made these experiments by growing sweet potato in Wagner's pot in order to probe the effects of soil air composition, soil bulk density and their interaction on the growth and yield of crops. Six treatments were made: two levels of soil air composition (the treatment where N gas was injected in the soil to decrease O2 concentration, and standard treatment), three levels of soil bulk density (loose, medium and compaction treatments), and their combination. The managing period was 42 days since the 76th day after planting when tuber-thickening stage of sweet potato (from August 23 to October 4). The results obtained may be summarized as follows. 1) As the soil became denser, total dry weight and the weight of tuberous root became smaller, and further the rate of the weight of tuberous root against total weight also decreased, which worsened the distribution of dry matter to the weight of tuberous root. However, the weight of the top parts and non-tuberous root was not affected so much by soil bulk density, and made little difference from that of the standard treatment. 2) When N gas was injected in the soil to decrease O2 concentration in soil air, total dry weight decreased in loose soil, but in the compact soil it was liable to be about the same as that of the standard treatment or to become somewhat greater. Whether the soil was compact or loose, tuberous root was hindered from thikening by N gas injection and decreased in production. It was found that the thickening of tuberous root was affected by soil air composition in the loose soil much more than in the compact soil. It was also observed that the rate of the weight of tuberous root against total weight was decreased by N gas injection treatment. On the other hand, the weight of the top parts and non-tuberous root was liable to become somewhat greater, probably because the thickening of tuberous root was checked by N gas injection treatment. 3) The authors examined the interaction of the effects of soil air composition and soil bulk density on the weight of tuberous root. As a result, it was found that when the soil was made compaction and further O2 concentration in siol air was decreased the thickening of tuberous root was hampered considerably and decreased in production. In this case, the effects of the decrease of O2 concentration in soil air were relatively small under the condition of compact soil.

[学科分类] 农业科学（综合）