Physical Characteristics and Crop Growth of Wet Upland Soils in Tokachi District (I) Physical Properties and Root System Development of Sugar Beet of Wet Andosol

Abstract

The productivity of Wet Andosol in Tokachi district is lower than that of Andosol in the same district. As a result, yields of sugar beet in Wet Andosol have been lower. For the purpose of clarifying the physical characteristic of these soils at present state, soil physical properties as well as the root systems of sugar beet were investigated in Wet Andosol and Andosol located in the same upland field. 1. Porosity filled with gravitational water as well as the porosity from —3.1 to —31.0 kPa of the sub-layer in Wet Andosol were remarkably lower than those of Andosol. 2. Soil water potential of Wet Andosol was kept from 0 to —13.1 kPa in layers below 45 cm for 11 days after rain-fall. On the other hand, soil water potential of Andosol was kept from -3.3 to — 22.9 kPa in corresponding layers. 3. Gaseous phase ratio in Wet Andosol was kept lower than 0.03 m3m'3 in layers from 45 to 75 cm for 11 days after rain-fall, while it increased to 0.08 m3m'3 in layer at 85 cm. On the other hand, the gaseous phase ratio in Andosol was kept larger than 0.18 m3 m'3 in layers below 45 cm during the same period. 4. Length and number of the root of sugar beet in layers below 40 cm of Wet Andosol were extremely low in latter part of July. On the other hand, root of sugar beet was developed to lower layers and more abundantly in Andosol. 5. Growth and yield of sugar beet in Wet Andosol were inferior to those in Andosol. From the above results, the lower growth and yields of sugar beet in Wet Andosol are considered to be caused by the lower gaseous phase ratio, which resulted in the poor root development as well as the poor water absorption by root.