Application Study Of Soil Loss Equation Under Different Land Utilization Type In The Upper Reaches Of Jialingjiang River

This paper selects universal soil loss equation (USLE) as the basic model, take the vegetation of five watersheds in soil and water loss locating observing station (Wanchang watershed, Guangyuan city) as the research subject, which locates in low mountain rainstorm area of the north of Sichuan Province. The rainfall erosion force factor R, the terrian factor LS of each catchment and the soil erodibility factor K were obtained though collecting and measuring the research area's rainfall data, the area of different land use, the slope and length, the soil physical properties and the organic content, the tree high and diameter, the forest canopy density and the grass cover degree, the weed area, the thin root (＜1mm) content, the litter amount, the shrub and herb amount. Each influence factors of vegetation and soil loss amount concerned with vegetation are studied. The results indicated that:1 11 rainfalls of the moderate rain, the heavy rain and the rainstorm was selected to do single correlated analysis between the products of all levels rainfall's kinetic energy E and their biggest rainfall intensity I_t in a certain period and the sediment yielding, and then the rainfall erosion force factor R∑E I₃₀ was obtained according to the national general indexes. The formula R=sum from 1 to 12 [1.735×10^{1.5×1g(P_i2)/P-0.8188}] can be used to calculate the average rainfall eroding force of many years, but it is not adapted to calculate Rof each year. The formula which is used to calculate the rainfall eroding force of a certain by Wang Wan-zhong is Rc=1.67 (PcI₆₀/100)^0.953, taking∑E I₃₀ as the rainfall agents of erosion target, it can estimate the annual rainfall eroding force well.2 On the basis of soil granule and soil aggregate composition data of each type land use, aided by fractal model, each kind soil the pellet and the crumb fractal dimension was gain, By studying the soil pellet fractal dimension and the pellet machinery composition and looks up the soil nomogram, several laws of the factor K was obtained: Compared with the returned lands and the corn lands, various forest lands soil pellet fractal dimension was less; Compared with 2.8633 measured 15 years ago, the soil pellet fractal dimension 2.8592 reduced now, the soil pellet condition improves; The decided factors of the soil pellet fractal dimension size is the content that the soil granularity was less than 0.002mm and the relations between them is extremely remarkable. Because all of them had remarkable relations with the content of the clay, the K value and the soil pellet fractal dimension was significantly negatively correlated. For the soil erosion research, the soil pellet fractal dimension is worse then the K value.3 Do regression analysis between all sample datas of August, 2006 and runoff field data of 1993, then we can get the closing formula Y=0.0026+0.411H+0.0705D-0.0677H*D in which tree high and tree diameter at chest height is the independent variable, the dependent coefficient R=0.8530, F examination is extremely remarkable. In short-time the relationship between tree high, tree diameter at chest height and number of days is: H=-0.0215+0.0078X-0.000021X², D=-0.0747+0.0109X-0.000018X², the correlation coefficient respectively is 0.9989 and the 0.9939, F examination reaches extremely obvious.4 The vegetation correlated soil loss Y and each influence factor of vegetation factor: The relation formula Y=e^{-6.6230+14.4517H-0.2389X5-5.1400X7} is the most reasonable formula which is about rainfall erosion of each time; The relation formula Y=e^{-5.0912+5.8478H+8.9274X1-6.3377X2-0.1134X6} is the most reasonable formula which is about rainfall eroding of each year. The formula above can be used to estimate the soil loss amount related to vegetation, further through A=RKLSY computing rainfall soil eroding quantity of each time and each year.5 Computing every kind of landuse vegetation related rainfall soil loss of each time and each year Y. When big, moderate rain and rainstorm, the Y value size order is always the masson pine pinus elliottii mixed forest＜the wetland pinery (on slope)＜the wetland pinery (lower part slope)＜the locust tree forest＜the locust tree pinus elliottii mixed forest＜the thin forest, to the soil protection effect, the conifer forest is better than broad leaved forest. For annual rainfall erosion, the Y value ordered: Locust tree forest＜wetland pinery (on slope)＜locust tree pinus elliottii mixed forest＜wetland pinery (lower part slope)＜masson pine pinus elliottii mixed forest＜thin forest. In those orders of Y, the change of the masson pine pinus elliottii mixed forest is the biggest, also the coniferous forest annual rainfall corrodes the Y value is bigger than the foliage forest, the primary cause is that in the coniferous forest withers and falls the decomposition is relatively slow, the stock on hard compares the foliage forest to be big, in the forest fills the grass quantity to be small; In the each time rainfall formula the factor selected is withers, but in the annual rainfall formula the selected fills the grass quantity.