We carried out an experiment with the effect on wind erosion prevention of the roller pressing upon the clean-tilled wheat field.
1. Moment of resistance of the soil.
The resistance near the surface of the ground is remarkably greater in the area pressed by the roller than in the area pressed by foot. However, no noticeable difference is found in the depth of 11 or 12cm. It indicates that the cultivation has reached up to that depth. As to the deeper part, the moment of resistance of the soil itself is shown. The increase of moment of resistance heightens the separation resistance and the drag resistance, and it shows that non-erosiveness is also greater.
2. Water contained by the soil.
The amount of water contained in the surface soil in the roller-pressed area is a little more than in the foot-pressed area. That is considered to be due to the fact that the pressure has decreased the porosity of the soil and facilitated the rising of the capillary water.
3. Nature of the surface.
The projection of the earth on the surface is 0.3-0.5cm. in the foot-pressed area, and 4.0-5.0m. in the footpressed. The condition for the starting motion of the soil particles is that the force that the particles get from the wind becomes equal to the static frictional pressure on the particles. Then the friction velocity when the particles start to move is represented by
V
*t=A√σ/ρgd
In the case of the roller-pressing V
*t is smaller and the more nonerosiveness is to be found than in the case of the foot-pressing.
4. Amount of flying soil.
The amount of flying soil in the roller-pressed area is very little, 26% of that in the foot-pressed. In the time when frost forms in the ground, the amount is small in either area, and the difference is little. Consequently, it is concluded that the roller-pressing is most efficacious at the period from March to the beginning of April, when frost ceases to fall.
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