Studies on Root-Breaking in Certain Crop Plants Caused by the Formation of IcicIe-Layer in the Ground and on Protection Methods against Them : 3. Formation of Ground-Cavity and Its Relation to the Plant Roots

[摘要] When we observe the profile of frozen soil, we find frequently a cavity formed underneath the root system of a plant. Its profile shows a lenticular shape generally, but sometimes it shows a different one. Under the ridge of rye, cavities are often connected each other and make a long hole like a tunnel along the ridge. Cavities can be found under any kind of crops-rye, wheat, barley, rape, hairy vetch, red clover and orchardgrass, and even under the stubble of plants-maize, millets, soybeans and weeds. The plant roots are found cut by such a cavity formed underneath them. The condition of the cavity varies with the development of the root system. The more vigorous the growth the deeper is the place of its formation under the same kind of plant. When the plant has very poorly developed root system, its roots are cut directly by the icicle layer without forming cavities. Therefore, the formation of cavity is much related to the field practice of crop cultivation. On the inner surface of cavity there are ice crystals, which may be considered as sublimates of vapor from unbrozen part of the soil. The mechanism of cavity formation will be explalined as follows. In the process of icicle-layer formation, it develops spreading horizontally beneath the frozen layer in the soil; but at the parts straightly below the plants, the icicle formation is avoided by the dense distribution of plant roots. With the thickening development of the icicle-layer the frozen surface soil layer is heaved as a whole, and the plant bodies grasp in the latter with their roots are pushed upwards, remaining cavities beneath it, and thus the roots distributed there are stretched and broken finallly (Fig. 2).

[学科分类] 农业科学（综合）