Studies on the Effects of Soil Physical Conditions on the Growth and Yield of Crop Plants : IV. Effects of the different soil Structures on a few plysiological characters of sweet potato plants.

Abstract

These experiments were made on the relationship between the effects of soil structure on the growth and yield of sweet potato Plant, and a few physiological characteristics. The results obtained may be sammarized as follows. (1) By aggregating the soil, the growth of sweet potato plant was promoted and its total dry weight increased. As for the relationship between soil treatment and growth of different stage, it was found that the aggregate formation of the soil affected its growth in its late growth stage to a large extent and promoted especially the thickening of tuberous root. When the soil was made compact, the growth of the top parts of the plant became flourishing, but the thickening of its tuberous root was hampered considerably. (2) The authors examined the internal tissure of sweet potato's root in the aggregated soil treatment. As a result, it was found that the activity of cambium was vigorous and that the number of primary xylem was few. It was also observed that its root presented the condition liable to become tuberous root, and that the differentiation of root had advanced. (3) The nitrogen content of sweet potato was larger in the aggregated soil treatment than in the standard soil treatment, and the rate of soluble nitrogen content against total nitrogen content was liable to be higher in the standard soil treatment. (4) The phosphorylase and amylase activity in tuberous root of sweet potato was lower in its early growth stage, highest in its middle growth stage, and decreased slightly in its late growth stage. The value of isoelectric point of cell protoplasm of parenchyma in tuberous root was low in its early growth stage and became higher as its growth advanced. (5) With regard to the relationship between the soil managing methods and a few emyzme activities, phosphorylase activity was higher in the standard soil treatment in its early growth stage, but decreased in and after its middle growth stage, whereas amylase activity was higher in the aggregated soil treatment in its early growth stage but decreased in and after its middle growth stage. All this goes to show that the aggregated soil treatment offered more favourable internal conditions for the accumulation of starch in tuberous root than the standard soil treatment.