This study aims to clarify the redox potential and the removal of soluble elements (iron, manganese, potassium, calcium) in a stratified paddy field using a large lysimeter (length 15 m) with an open system percolation in the subsoil. As a result, plow layer and plowsole layer became the closed system percolation for the whole year. At every investigated point (2.5 m, 5.0 m, 10.0 m and 15.0 m) from the atmosphere (edge of the lysimeter), both layers became reduction layers. Subsoil became the open system percolation and oxidation layer at every point.
Four elements in downward water were detected in plow layer and plowsole at every point for the whole year. Iron element and manganese element weren’t detected in downward water of the subsoil at every point for the whole year. Potassium element and calcium element were detected at every point for the whole year and their concentrations in subsoil tend to be higher in the plow layer and plowsol. The concentrations of the four elements in the downward water increased in summer and decreased in winter. When the experiment finished, we found iron and manganese illuvial horizon in the upper subsoil.
This study aims to clarify the fluctuation of concentrations of gas component : oxygen, carbon dioxide, in the subsoil of open system percolation at a stratified paddy field using a large lysimeter (length 15 m) for two years. Soil air extracted at 37 cm depth was selected from the exposed edge of the large lysimeter to the opposite edge of the lysimeter (2.5 m, 5.0 m,10.0 m,15.0 m horizontally from the edge), rhe stratified paddy field kept inundation for two years and air penetration occurred horizontally. The first year, the field was barren but the second year, rice was planted. Oxygen concentrations in the layer of the open system percolation decreased in summer but increased in winter. Carbon dioxide concentrations increased in summer but decreased in winter. It was thought that these annual changes depended upon soil temperature. The oxygen concentration lowered with the horizontal distance from the exposed edge, whereas the carbon dioxide concentration heightened with distance. Formation of carbon dioxide was only equal to oxygen consumption at 2.5 m from the exposed edge. The redox potential at 10.0 m and 15.0 m lowered when the oxygen concentration became lower than 2%. Then at 15.0 m elements of iron and manganese were detected in the downward water in the subsoil.
Volcanic soil can be easily degraded under natural conditions or when subjected to human activities. A research was conducted in Java and Bali islands in Indonesia to determine the relationship between soil characteristics, farming system and conservation strategies in highland volcanic areas. The volcanic soils in the research areas were found to have high fertility but low organic matter content. Also, soils with high clay content tend to have low erodibility. On other hand, low clay content, low cation exchange capacity (CEC), low liquid limit (LL) and low plasticity limit (PL) are associated with high soil erodibility. The common farming systems in the research areas are growing vegetables and raising livestock. Multiple cropping is the predominant system as exemplified by relay cropping, sequential cropping and intercropping. To control soil erosion, both agronomic and mechanical measures are practiced. Farmland agroforestry and a combination of “Taungya” and multistory agroforestry are common agronomic control strategies while vertical ridges with grass strips and bench terracing, especially on steep locations are the mechanical measures widely adopted. The attainment of effective soil erosion control and increased land productivity largely depend on the establishment of appropriate measures and conservation strategies.
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.
Some factors relating to soil erosion were analyzed on the purpose of conservation of sloping farmlands with USLE at Ansai district in the Loess Plateau, China. The results indicated that the rainfall and runoff factor R of USLE is lower than 100 tf-m2/ha-h. The soil erodibility factor K of the Loess was relatively large value. The topographic factors Ls of sloping farmlands were very large value. These factors indicate that a serious erosion is caused by not only rainfall but also by characteristics of soil and landuse on hill-slopes in the Loess Plateau. The conditions of the surface and subsurface of the hill-slopes were also investigated. The result indicated different conditions by the direction of the slope. For example, soil moisture of north faced slope was higher than that of south faced slope, but soil hardness of north faced slope was lower than that of south faced slope. These differences are caused by meteorological factors and influence soil conservation on hill-slopes.