Studies on Root-Breaking in Certain Crop Plants Caused by Icicle-Layers Developing in the Ground and Protection Measures against the Damage : 4. The density of the root development as a factor affecting the formation of icicle-layers. : 5. Planting methods in relation to root-breaking.

[摘要] It is not unusual that plant roots are found growing undamaged even under freezing grounds where the formation of icicle-layers destructive to them are prevailing. The facts had been found by the author's previous studies that the density of the root system was particularly large at such localities in the ground, and that no icicle-layers were formed there. It may be natural to expect that there should exist intimate relations between the density of the root and the amount r of soil water content because the amount of the icicle-layer in the frozen soil may be represented as that of the water content. For the purpose of investigating the relations, 32 samples of frozen soil were taken from a pasture sown to orchardgrass, and their water contents and root contents were determined. The correlation between those two is shown in Fig. 1, the correlation coefficient γ being -0.475 (P<0.01). It means that the more the density of root is the less the water content. in the frozen soil. The density of root development may therfore be considered to possess. the ability to prevent the formation of icicle-layers in the ground. The intensity of the damage in plants caused by icicle-layers were observed to vary according to the planting methods. Wheat plants sown 10 days later (Fig. 2b) than the proper time, suffered rather heavy root-breaking damages by comparatively shallow location of the "cavity" formed as compared with plants sown timely (Fig. 2a). Wheat plants sown 20 days later than the proper date (Fig. 2c) were more violently damaged with no cavities being formed in the ground. Wheat plants without sufficient supply of fertilizers or manures recieved similarly serious damages as those sown not timely, in accordance to the amount of fertilizers. Planting ways also may have effects on the root-breaking. Wheat plants sown in one row on a ridge (Fig. 2d) were found to be violently damaged by icicle-layers formed closely near, the plant and by cavities formed at a shallow position. Of the wheat plants sown in more than 3 rows on a ridge (Fig. 2, d, e) the inner rows recieved almost no damages. In the case of five rows on a ridge, cavities were formes below the inner rows of the plants (Fig. 2d). But on the contrary cavities were formed below the outermost rows in the case of more than five rows on a ridge (Fig. 2e). Therefore, timely sowing, sufficient fertilizing and a proper planting rate should be recommended in cold regions, because those treatments may avoid the injury in plants preventing the formation of icicle-layers.

[学科分类] 农业科学（综合）