Study on the control of wind-erosion

Abstract

The expeiment with the wind erosion was carried out on clean-tilled wheat field and the kittatemaki field (that is, wheat field sown on fallowed soil in use of stubbles of the previous crop).1. Wind velocityBy the investigations of the horizontal distributions of wind velocity, it was made clear that the clean-tilled field and kittaternaki field were below the similar condition of wind.On the ridges in the kittatemaki field, the wind velocity decreased vertically about up to the height of 45cm. As for the influence of particular ridges on vertical distribution of wind velocity, the velocitybecomes constant at about the fifth ridge from the windward. The nature of the surfaces of both fields is as tabulated hereunder, according the formula of the curve of vertical distribution of wind velocity-:U(z)=5.75U*logz/KIt is remarkable that the value of U* is very large, and this is thas the value is the total friction velocity of the surface and the ridge.U*……Total friction velocity of surface and ridge, U′*……Friction velocity of ridge.U*-U′*=U″*The above formula is the friction velocity of the surface soil. The following is the deduced value.U″*=17.4m/secAccording to the formula of the coefficient of resistance (CX), ρU*21=1/2ρUm2C×hd+ρV″21∴C×=0.28This means that the ridge makes the wind velocity required to the initial movement increase almost by 1.70 times of the soil.2. Soil moistureThe quantity of water contained near the surface is less from 4 to 6% in the clean-tilled field than in the kittatemaki field. The causes are considered to be (1) the cutting-off the capillary tubes owing to tillage, (2) the exposure of the surface soil to the wind, and (3) the limitation of sunshine by the ridge, and so forth.3. Flying soil.The quantity of flying soil in the clean-tilled wheat field amounts to more than 4 to 5 times of that in the kittatemaki field. As regards the height distribution of flying soil, in the case of the former the majority of the particles near the surface are of great diameters, but according as the height increases, particles of small diameter are found to increase. On the other hand, in the case of the latter the diameters do not vary according to the height from the ground.This shows that in the clean-tilled the flying soil is mostly from its own surface, while in the other it consists mainly of the soil carried from the fields to its windward.