| Soil surface roughness is one of the main factors affecting soil erosion intensity and the main contents at present. By the way of combining methods among the artificial simulated rainfall experiments, geophysicists and fractal theory, distribution characteristic and evolvement rule of soil surface roughness was carried out, and quantitative coupling relationships between soil surface roughness and runoff, sediment yield were also explored on the condition of different artificial management practices of slope farmland on the loess area. At the same time, the corresponding description models of soil surface roughness to different management practices were established on the base of comprehensive analysis. The research would help to clarify the relationship between the evolvement characteristic of soil surface roughness and soil erosion, and provide scientific theory basis and technical support for understanding the mechanism of water erosion and soil erosion prediction further, and it would also serve on the management of sloping field.1. Soil physical properties and rainfall effect on surface roughness were analyzed, and slope gradients effect on soil erosion under the different soil surface conditions also was explored. The results were as following.(1)On the condition of rainfall density, the variation of soil surface roughness increased with the increasing of soil physical clay gradually. The variation of soil surface roughness decreased generally with the increasing of soil bulk density and soil moisture content .The variations to slope with straight (CK) was the higher than those of artificial management practices during the course of rainfall. (2) The variation of soil surface roughness decreased generally on the condition of rainfall. The variation was stable during the small rainfall density and the variation was obvious when rainfall density was over 0.99 mm/min.The variation of soil surface roughness were decreased in an exponent function gradually with the increasing combinating factor of rainfall(PI). (3)On the condition of rainfall intensity from 0.50 to 1.00 mm/min and 2.00 mm/min, the maximum runoff appeared to the 20°for the soil surface of medium-roughness and 25°for soil surface of the roughness. On the condition of rainfall intensity of 1.50 mm/min, the maximum runoff appeared to the 25°for the soil surface of the medium-roughness and the roughness. On the condition of rainfall intensity of 2.50 mm/min, the maximum runoff appeared to the 15°for the soil surface of medium-roughness and surface of the roughness. On the condition of rainfall intensity from 0.50 to 2.00 mm/min, the maximum sediment appeared to the 20°for the soil surface of the medium-roughness and the roughness.On the condition of rainfall intensity of 2.50 mm/min, the maximum sediment appeared to the 15°for the soil surface of medium-roughness and the roughness.2. Evolvement rules and effects of soil surface roughness were clarified during the course of splash erosion. The results were as shown. (1) On the condition of rainfall intensity of 1.53 mm/min, the splash erosion content of downslope was higher than that of upslope with the increasing soil surface roughness. The variations of splash erosion content of downslope, splash erosion content of upslope and total splash erosion content showed that were from the increasing to the decreasing with the increasing soil surface roughness. On the condition of rainfall intensity of 0.62 mm/min, the variations of splash erosion content of upslope were from the increasing to the decreasing with the increasing soil surface roughness. Splash erosion content of downslope and total splash erosion content showed those were from the increasing, the decreasing to the increasing nearly with the increasing soil surface roughness. On the condition of the above rainfall, the variations of splash erosion content of downslope, splash erosion content of upslope and total splash erosion content of artificial management practices were the higher than the variations to the slope with straight (CK).(2) On the condition of rainfall intensity of 0.62 mm/min, the evolvement characteristics of soil surface roughness to the slope with rake was consistent to the slope with straight (CK) that soil surface roughness was increased with the increasing rainfall energy. However, the other artificial management practices were decreased with the increasing rainfall energy. The variation of soil surface roughness was from the decreasing to the increasing with the increasing splash erosion. On the condition of rainfall intensity of 1.53 mm/min, the evolvement characteristics of soil surface roughness to the artificial management practices were opposite to those of the slope with straight (CK) that soil surface roughness was increased with the increasing rainfall energy. The variation of soil surface roughness was also increased with the increasing splash erosion.(3) The variations of soil surface roughness and splash erosion to the rake slope were consistent to the slope with straight (CK) that they were increased with the increasing combinating rainfall intensity. The evolvement characteristics of soil surface roughness to the other practices were from the decreasing to the increasing with the increasing combinating rainfall intensity. However, the total splash erosion of the other practices was from the increasing to the decreasing with the increasing combinating rainfall intensity.3. Evolvement rules and effects of soil surface roughness were clarified during the course of soil sheet erosion and rill erosion. The results were as shown. (1) On the condition of rainfall intensity of 0.67 mm/min, the runoff volume and sediment yeild were from the decreasing to the stable trend with the increasing soil surface roughness. However, on the condition of rainfall intensity of 1.63 mm/min, the runoff and sediment concentration were the decreasing trend with the increasing soil surface roughness, and the total contents were the higher than that of the condition of rainfall intensity of 0.67 mm/min. The runoff volume and sediment yeild of artificial management practices were all lower than those of the slope with straight (CK) on the condition of different rainfall intensity.(2)On the stage of sheet erosion, the evolvement characteristics of soil surface roughness to the slope with rake was opposite to the slope with straight (CK) that soil surface roughness was increased on the condition of heavy rain and decreased on the condition of light rain. Soil surface roughness of the slope with hoe was increased on the condition of different rainfall intensity. Soil surface roughness of the slope with dig and the with slope contour were decreased on the condition of different rainfall intensity.(3) On the condition of rainfall intensity of 0.67 mm/min,runoff volume was from the decreasing ,the increasing to the decreasing trend and sediment yield was general the decreasing trend with the increasing soil surface roughness, and the sediment yield was all lower than that of the slope with straight (CK).On the condition of rainfall intensity of 1.63 mm/min, runoff volume was the decreasing trend and sediment yield was from the decreasing ,the increasing to the increasing trend with the increasing soil surface roughness, and the runoff volume and sediment yield were also lower than those of the slope with straight (CK).(4) On the stage of rill erosion, Soil surface roughness of the slope with rake and the slope with hoe were increased on the condition of different rainfall intensity. Soil surface roughness of the slope with dig and the slope with contour were decreased on the condition of different rainfall intensity. The evolvement characteristic of soil surface roughness to the slope with straight (CK) was opposite to the sheet erosion.(5)During the course of continuous rainfall, the runoff volume and sediment yield of artificial management practices slope were decreased gradually with the increasing soil surface roughness, and the lower than those of the slope with straight (CK) on the condition of the first and second rainfall. The variations of runoff volume and sediment yield were comparative complex, and sediment yields of the slope with artificial management practices were the higher than those of the slope with straight (CK) on the condition of the third rainfall.(6) During the course of continuous rainfall, the evolvement characteristic of soil surface roughness to the slope with rake was consistent to the slope with straight (CK) that soil surface roughness was increased with the increasing rainfall intensity. However, soil surface roughness of the other artificial management practices were from the decreasing to the increasing trend with the increasing rainfall intensity.4. Distribution characteristics of soil surface roughness were revealed and theoretical description models of soil surface roughness were obtained. The results were as shown. (1)The different methods of soil surface roughness were analyzed through the contrast. The results were obtained that the method of laser scanning was best, and the followings were the method of the contact pin meter, roller chain method, method of staffs and ruler in turn.(2) Soil surface microrelief had the self-affine features to the rake slope and the slope with straight (CK), however, soil surface microrelief had the self-similar features to the slope with hoe and the slope with dig in the aspects of the different directions. It had self-similar features in the parallel to slope and had self-affine features in the vertical to slope to the slope with contour.(3) The self-similar surface roughness could be simulated through the Fractional Brownian motion function, and the self-affine surface roughness could be simulated through the logarithm transform of the structure function. The models were relatively reasonable by the way of experimental tests. On the base of the above, the optimal combinating parameters to describe soil surface roughness were put forward.5. Quantitative coupling relationships between soil surface roughness and runoff, sediment yeild clarified during the course of soil erosion. The results were as shown.(1) On the stage of sheet erosion, the runoff was increased with the increasing variation of soil surface roughness to the self-similar fractal soil surface. However, on the stage of rill erosion, the runoff was decreased with the increasing variation of soil surface roughness to the self-similar fractal soil surface. The runoff was opposite to the self-similar fractal soil surface on the condition of different features soil surface.(2) On the stage of sheet erosion, the sediment yield was decreased with the increasing variation of soil surface roughness to the self-similar fractal soil surface. However, on the stage of rill erosion, the sediment yield was increased with the increasing variation of soil surface roughness to the self-similar fractal soil surface. The runoff was consistent to the self-similar fractal soil surface on the condition of different features soil surface.
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