Abstract
Aggregate structure is said to be the ideal soil structure for plant growth, because it has high water permeability together with high water retention capacity. When considering arid land afforestation, the high water permeability and high water retention capacity are essential to utilize the limited amount of water for plant growth. In the present study, artificial aggregate formation was performed in order to improve the water permeability and water retention capacity. Some kinds of soil conditioners, minced worm, humic acid, gypsum and leaves of Eucalyptus camaldulensis (E.C.) thought to be effective to form aggregates, were mixed with wet black soil. The mixed effect of soil conditioners was quantitatively estimated by the aggregate fraction, the water retention capacity and water permeability. After mixing a soil conditioner, increase in the aggregate fraction was found in the order of humic acid < gypsum < minced worm < leaves of E.C. This effect was continued for 20 months. And the water permeability of each soil sample was high in the same older. The water retention capacity was estimated in pF (log|-cmH2O|) range between 1.8-4.2, where the soil water is available to plant growth. The soil mixed with humic acid and gypsum was increase in both of the water permeability and water retention capacity. The effect of aggregate formation on these physical properties of soil was discussed.
