| Because of the low vegetation coverage, the insufficient soil anti-erosion ability, and the highly concentrated rainfall distribution in Loess Plateau the soil and water erosion was serious, the land resources was damaged, the soil fertility declinesand the ecological environment becomes fragile in this area. The vegetation has great influence on the soil erosion, and artificial grassland could reduce the soil erosion significantly and accumulate precipitation in rainy season. In our country, Leymus chinensis was concentrated in the Northeast China Plain and the eastern of Inner Mongolia plateau, and also distributed in the Shaanxi, Ningxia, Gansu and other province. It was one kind of forage grasses that was most widely distributed and the highest valued. It was important for us to prevent and control water and soil loss that analysis of the influence of Leymus chinensis coverage on runoff and wind erosion process and revealled the benefit of soil and water conservation of the Leymus chinensis. Through artificial rainfall simulation experiment and wind tunnel experiments, the author studies the runoff and sediment characteristics and anti-erosion properties of 5 kinds of Leymus chinensis coverage, discussing the effects of soil and water conservation in different coverage. The results showed that:1. Under simulated rainfall condition, the initial runoff gradually delaied with the Leymus chinensis coverage increasing. The greater the slope gradient was, the faster the initial runoff time was; the greater the rainfall intensity was, the faster the initial runoff time was. When the Leymus chinensis coverage was less than 60%, the influence of coverage on initial runoff time was relatively small. When the Leymus chinensis coverage was 100%, the runoff time was the slowest. The initial runoff time was the slowest when the slope gradient was 5°. With the slope gradient gradually increasing, the increasing rate of initial runoff time increases. The initial runoff time of the loessial soil was faster than the sandy soil. The effect of the Leymus chinensis coverage on different soil types was relatively stable. When the Leymus chinensis coverage gradually increases, the initial runoff time lagging rate of the sandy soil changes insignificantly compared with the loessal soil.2. Under the same slope gradient and rainfall intensity, with increasing coverage of Leymus chinensis, the accumulate runoff volume showed a decreasing tendency. The slope gradient and rainfall intensity was also the important factor affecting accumulate runoff volume. When the coverage was 20%, the average accumulate runoff volume was 76.15 L/( m2·h), Leymus chinensis coverage increased to 100%, and the average cumulative runoff volume decreased by 44%. The greater the slope gradient was, the greater the accumulate runoff volume was. When the slope gradient increased from 5° to 15°, the average accumulate runoff volume increased by 26%. The greater the rainfall intensity was, the greater the accumulate runoff volume was. When the rainfall intensity increased from 90mm/h to 120mm/h, the average cumulative runoff volume increased by 42%. The accumulate runoff volume of sandy soil was less than the loessial soil. With the increasing of Leymus chinensis coverage, the average reducing rate of the accumulate runoff volume of sandy soil first decreased and then increased compared with the loessial soil. When the Leymus chinensis coverage was 60%, the reduction rate reaches the minimum.3. Leymus chinensis coverage, slope gradient and rainfall intensity were important factors affecting the accumulate sediment yield. The accumulate sediment yield was inversely related to the coverage and proportional to the slope gradient and rainfall intensity. When the Leymus chinensis coverage increased from 20% to 100%, the average accumulate sediment yield decreased by 65%; when the slope gradient increased from 5 ° to 15 °, the average accumulate sediment yield increased by 63%; when rainfall intensity increased from 90mm/h to 120mm/h, the average acumulate sediment yield increased by 79%. The accumulate sediment sediment yield of sandy soil was greater than the loessial soil. When the Leymus chinensis coverage was less than 60%, the average increasing rate of the accumulate sediment yield of sandy soil slowly increased with the Leymus chinensis coverage increasing compared with loessial soil. When the coverage was greater than 60%, the increasing rate of the accumulate sediment yield of sandy soil increased rapidly.4. The runoff trend of loessial soil and sandy soil of Leymus chinensis showed a rapid growth in the early stage of rainfall and stable in the late rainfall. And the sediment trend showed a rapid growth and then slightly declined in the early stage of rainfall and keeps stable in the late rainfall. At every stage of rainfall, the runoff rate loessial soil was higher than the corresponding condition of sand soil and the sediment yield was less. This feature was the most obvious when rainfall intensity was 120mm/h, the slope gradient was 15° and Leymus chinensis coverage was 20%.5. The amount of wind erosion was inversely related to the coverage and proportional to the wind speed. The amount of wind erosion of loessial soil was lower than the corresponding condition of sandy soil. When the Leymus chinensis coverage increased from 60% to 80%, the reducing rate of the amount of wind erosion was the biggest, therefore, the critical coverage of erosion resistance of Leymus chinensis was 60- 80%. It was close of the amount of wind erosion that was collected in the two layers of 0-23 cm. it was mainly composed of creep particles and most transition particles, sediments collected in this highly overall wind erosion accounts for more than 70%.6. The coverage of artificial Leymus chinensis was large, so as to effectively prevent the soil wind erosion. Compared with wormwood, Leymus chinensis decrease the corrosion rate of 37.47%. Stubble could effectively prevent water loss and soil erosion, compared with the commune, buckwheat stubble could reduce the corrosion rate of 62.01%, corn stubble could reduce the corrosion rate of 70.99%. The erosion reduction rate of artificial Leymus chinensis stubble was close to the corn stubble. |
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