| Soil surface roughness (SSR) is an uneven surface phenomena caused by combined natural and human factors of soil lump, agglomerates size, crop planting and human land management or rain splash, runoff scouring in the certain areas. It is highly recognized because that it is one of the main effects on the storage and direction of overland runoff, erosion and sediment yield. However, it is difficult to simulate spatial distribution characteristics of SSR, and especially there hasn't an ideal method about the calculation of SSR, research in this area still in the exploratory stage, which has badly affected people's recognition on the effects of SSR in the erosion process. Given above, SSR caused by widely used artificial backhoe, artificial digging and tillage practices such as contour farming on the sloping land (bare surface) of the loess plateau was studied, and firstly SSR was determined by laser scanner, and then micro-DEM under different tillage practices was established with the GIS technology, as well as spatial distribution characteristics of SSR under different tillage practices were analyzed according to the fractal and fractal dimension theory, and finally models describing SSR of the loess sloping land were established, aiming at providing scientific basis for the profound revelation in the evolution characteristics and erosion responding laws of SSR in the soil erosion process. The main conclusions showed as follows:1. SSR under different tillage practices determined by laser scanner was statistically analyzed, which showed that standard deviation (Sd) of slope SSR under practices of contour farming, artificial backhoe and artificial digging was 0.031, 0.042 and 0.014 respectively; Deviation was 6.378, 8.587 and -1.263 respectively; Coefficient of variation (Cv) was 0.002, 0.003 and <0.001 respectively, which were all greater than the linear slope with standard deviation (0.003), deviation(0.498) and variation coefficient (<0.001). Above suggested tillage practices significantly raised the fluctuation of slope and had a certain effect on the spatial distribution of slope elevation. Slope relative elevation among contour farming, artificial digging and artificial backhoe tended to the skewed normal distribution compared with the linear slope, but these variation coefficients of surface elevation were all smaller than 0.1, suggesting spatial variability of slope elevation was weak. Therefore Micro-DEM can be created by spatial interpolation methods.2. Interpolation accuracy of Micro-DEM established by GIS technology was analyzed, showing that root-mean-square errors of RBF interpolation, Kriging interpolation, local polynomial interpolation and inverse distance weighted interpolation were 46.6, 24.6, 21.0 and 18.0×10-3 respectively. This suggested the error produced by inverse distance weighted interpolation was smallest, which could be the establishment method of Micro-DEM in the slope land. Based on this, surface micro relief under different tillage practices was analyzed, showing that: (1) Raster statistic figures of micro slope under artificial backhoe and artificial digging first increased and then discreased with variation of micro gradient, and mainly distributed in the range of 10°～25°; Raster statistic figures of micro slope under contour farming increased with the increasing of micro gradient, and among this, raster whose micro gradient was greater than 40°was the most, accounted for 21.21% of the total.(2) As for sloping surfaces of artificial backhoe and artificial digging, the distribution trend of raster statistic figures of micro slope was simialr, which was successively south slope, southeast, southwest, west slope, esat slope, northwest, north slope, northeast slope and flat field; The micro slope of sloping surface under contour farming was mainly located in the south and north slope, and both raster figures accounted for 76.07% of the total, yet figures of other aspects were smaller. This suggested there was some difference between micro slope gradient and micro slope aspect under different tillage practices, which could have an effect on the spatial characteristics of slope SSR.3. Spatial characteristics of SSR under different tillage practices according to the fractal and fractal dimension was analyzed, showing that fractal dimension (DSMV) of linear slope, artificial digging, artificial backhoe and contour farming was in the range of 2.13～2.87, and crossover length (lSMV) varied in the range of 1.01～1.36. Under the condition that the value of q was [-10,10], SSR under different tillage practices presented obvious asymmetry compared with the linear slope, and the fractal dimension increased with the increasing of SSR, yet corresponding crossover length decreased. Above features could be described by fractal and fractal dimension parameters of f (α)max,αmax,Δf (α)max, ( )Δf(α)min,αminandωα. Based on this, models describing SSR of loess slope land was proposed, that isSSR =ωa×f amax.4. Studies on the effects of SSR in the soil erosion process showed that (1) Surface filling and excavation amounts were mainly in the range of 1.00×10-5～1.00×10-4 m3 under manual digging and artificial backhoe. Moran's I of surface filling and excavation amounts was generally low (smaller than or equal to 0), suggesting that slope was the main factor impacting on the filling and excavation, but effects on the spatial autocorrelation were not obvious. (2) Runoff first increased and then tended to stable in the rainfall process, showing a Logarithmic relationship with rainfall time; Sediment first increased, then decreased and gradually maintained to stable; The order of surface runoff time was: linear slope< artificial backhoe < manual digging <contour tillage. Tillage practices could significantly diminished slope runoff and sediment compared with the linear slope. Runoff caused by contour farming, manual digging and artificial backhoe was diminished by 38.17%, 17.88%, 43% respectively and sediment was diminished by 65.6%, 36.3%, 23.4% respectively.(3) SSR had a significant effect on the characteristics of slope flow concentration, mainly including effects on the flow path and spatial distribution pattern. There was a significant linear negative relationship between flow concentration density and SSR, which suggested SSR had obvious soil and water protection effect. |
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