Studies on the Effects of Soil Physical Conditions on the Growth and Yield of Crop Plants : I. Effects of soil bulk density on the seed germination and growth of crop plants in their early growth stage.

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Experiments were made to probe the effects which the soils of different bulk densities would have on the conditions of crop plants in their early growth stage. 1) The authers, using a kind of crop plants, examined the effects which the soils of different bulk densities would have on their conditions observed in their early stage of growth. As a result, it was known that the effects in question are different according to the kind of crop plants. As a matter of fact, the growth of such kinds as soybean, buckwheat, Japanese radish, Chinese cabbage, cucumber and pumpkin was hampered considerably, whereas no remarkable growth-inhibiting effects were observed in the case of sorghum, upland rice and paddy rice under the high bulk density of soil. It was also observed that the growth of the roots of crop plants in its early stage was liable to be affected by the soil of high bulk density much more than that of the upper parts of such plants. 2) The germinating capacities of various types of crop plant seeds in water were compared with one another to probe the effects the controlled supply of oxygen would have on such capacities at the germinating time. The result was that those crop plants which had attained good germinating and growing conditions even under the controlled supply of oxygen were mostly those which were not easily affected by the relatively high bulk density of soil (in this case, correlation coefficient γ= + 0.62). 3) The effects which the soils of different structures would have on the early-stage growth of crop plants were examined by the use of the soils which were aggregated under the effect of soil conditioners, together with their original soils. Those crop plants whose growth conditions were considerably improved by the aggregated soil were Japanese radish and buckwheat, and no such effect was observed in the case of paddy rice and barnyard millet. 4) In studying the effects which the soils of different bulk densities and under different aerating conditions would have on the early-stage growth of crop plants, it was found that the effects in question were different on the kind of the crop plants used. That is, the growth of sweet potato plant and soybean was liable to be affected adversely when soil aeration was not good. In the case of corn, the growth was affected more by the soil strength than by the soil aerating conditions. As for upland rice, its growth was less affected by such soil physical conditions than three other crop plants.