17:15 〜 18:30
[AGE27-P07] Effect of the gravity differences on early stage water movement in soils.
キーワード：微小重力、レゴリス、土壌、浸透、水分保持
When considering the expansion of human activity to other planets, food production is one of the major issue. For plants growth, the dynamics of water in the soils are very important. Especially on other planets, the surface layers contains only primary weathering objects called regolith, and because of their low gravity, infiltration is unlikely to occur, and a lot of water is lost due to evaporation. Therefore, we investigated the initial water movement accompanied by the differences of gravity and soil structure. Standard sand, aggregate soil, macropore soils, and clayey soils were assumed as tested materials. Glass capillaries were used for the macropores.
The centrifugal force was used to generate the pseudo-gravity differences by rotating the tube rotator horizontally. For infiltration experiments, a 2ml centrifuge tube with a small hole at the bottom as water supply is placed on the soil surface in 15ml centrifuge tubes, then the tube was drained by applying the pseudo gravity. In the evaporation experiment, 2 ml of water was first supplied to the soil sample and placed in an incubator at a constant temperature of 40°C. In this experiment, gravity differences were made by changing the inclination of the sample.
Changes in gravity did not affect the infiltration depth as expected. In addition, although there was no significant difference in infiltration depth in all soils, macropore infiltration tended to be greater in standard sand than in clay soil, which was considered to be due to the influence of inertial force when the particle size was large. In the evaporation experiment, the gravity did not affect the amount of evaporation, but the soil structure did. The amount of evaporation of standard sand with macropore and aggregates was significantly higher than that of bare standard sand. Because the exposed surface area increases as the soil structure develops, the vapor exchange might be accelerated.
The results of this study indicate that soil moisture is easily lost due to the aggregate structure with organic matter and the macropore structure in which vascular plants grow. However, on the current 1G earth, the macropore soils have more organic matter and shows higher water retention capacity, and are advantageous for plant growth. We need to consider long-term experiment.
The centrifugal force was used to generate the pseudo-gravity differences by rotating the tube rotator horizontally. For infiltration experiments, a 2ml centrifuge tube with a small hole at the bottom as water supply is placed on the soil surface in 15ml centrifuge tubes, then the tube was drained by applying the pseudo gravity. In the evaporation experiment, 2 ml of water was first supplied to the soil sample and placed in an incubator at a constant temperature of 40°C. In this experiment, gravity differences were made by changing the inclination of the sample.
Changes in gravity did not affect the infiltration depth as expected. In addition, although there was no significant difference in infiltration depth in all soils, macropore infiltration tended to be greater in standard sand than in clay soil, which was considered to be due to the influence of inertial force when the particle size was large. In the evaporation experiment, the gravity did not affect the amount of evaporation, but the soil structure did. The amount of evaporation of standard sand with macropore and aggregates was significantly higher than that of bare standard sand. Because the exposed surface area increases as the soil structure develops, the vapor exchange might be accelerated.
The results of this study indicate that soil moisture is easily lost due to the aggregate structure with organic matter and the macropore structure in which vascular plants grow. However, on the current 1G earth, the macropore soils have more organic matter and shows higher water retention capacity, and are advantageous for plant growth. We need to consider long-term experiment.