Studies on the Effects of Soil Physical Conditions on the Growth and Yield of Crop Plants : III. Effects of the capacity and composition of soil air on the growth and yield of sweet potato plants.

Abstract

The authors clarified the relationship between the type of soil and various soil-managing methods (control of soil bulk density, moisture content, height of ridges and amount of fertilizers), on one hand, and the soil air capacity and the soil air composition, on the other, and studied the effects these factors would have on the growth and yield of the sweet potato plant. 1) The soil air capacity was found to decrease when the soil bulk density became higher or when the soil moisture content became larger. Also, the capacity in question was larger where the height of ridges was larger, than where the height in question was smaller. In terms of the type of soil, the capacity was smaller in the alluvial soil and larger in the volcanic ash soil. As for the change in the soil air capacity after tilling, the capacity decreased considerably in the alluvial soil with the lapse of time, while it decreased very slowly in the sandy soil. The air capacity of the volcanic ash soil was affected also by the soil-managing methods to a greater extent than that of the sandy soil. 2) In the brown-colored volcanic ash soil, the composition of air contained in it is closely related with its air capacity. The O₂ concentration in the air in question was lowered when the soil air capacity became smaller, and the CO₂ concentration in it increased under the same condition. But the effect was different depending on the type of soil a significant correlationship was observed between the soil air capacity and the CO₂ concentration in the soil air in the case of the alluvia soil and the volcanic ash soil, but no such correlationship was noticed in the case of the sandy soil and the aggregated alluvial soil. 3) With regard to the relationship between the soil air capacity and the composition of soil air, on one hand, and the growth and yield of the sweet potato plant, on the other, the growth of the upper parts of the plants was male active when the CO₂ concentration in the soil air was increased, whereas the growth of the tuberous roots was checked under the same condition, and as a result, the weight of the tuberous roots was reduced. All this goes to show that the soil air capacity needed to assure the growth of the upper parts of the plant is different from that required for the growth of the tuberous roots, and that therefore the different soil air capacities have their respective influences on the distribution of the substances produced through photosynthesis among the upper and underground parts of the plant.