A Study On The Characteristics Of Sand Flow Structure In Farmland Of Bashang,hebei Province

Bashang of Hebei Province, belonging to the Agro-pastoral ecotone,is an important sand source area of the group of mega-cities of Beijing and Tianjin on the upwind. Bashang has implemented the Grain for Green Project since 2000, and has achieved significant results in the ecological environment treatment. The regional farmland is dominated by dry large plots (flat, centralized and contiguous, and both the length and the width of per single farmland are more than 300m), and people still use traditional farming methods to cultivate there. Traditional farming methods can easily cause soil erosion and land desertification, or give rise to the huge loss of fine surface material and soil nutrients, decline the land productivity, or lead to the pollution of atmospheric environment, or even affect human beings'health. However, the current investigation of cropland erosion mechanism of dry farmland is so poor that it can not meet the actual needs of ecological construction. Structure of drifting sand flux is the core study of the cropland erosion mechanism; therefore, it is important and practical to carry out the study of the sand flow structure of dry farmland in Bashang , in Hebei Province.Based on this, this thesis select the typical area—KangBao County in Hebei Province, using field observations and wind tunnel simulation method to study the structure of drifting sand flux of sand fields, revealing the variations of cropland wind erosion intensity and structure of drifting sand flux in vertical direction and in horizontal direction under different tillage management practices, and thus it will provide a theoretical basis for the cropland erosion control and scientific estimation of the loss of soil erosion in this region.The results show that:(1) The surface aerodynamic roughness and farmland crop stubble high ridge are closely related. The rougher the surface is, the stronger the ability of anti-wind erosion will be.(2)The variation of structure of drifting sand flux in vertical direction: the wind-blown mass (Q) of stubble ground and grinding harrow tillage will reduce if the ground increases with height (H) from 0cm to 60cm, which is in line with the exponential rule Q=ae^bH; it will be in line with the power function Q=aHb( a, b are constants) in the height of 20-60cm; in the height of 0-20cm, the grinding harrow tillage meets exponential rule, however, the structure of drifting sand flux of stubble ground neither meets the exponential rule nor meets the power function because of the influence from the stubble, and it meets cubic polynomial Q=a+bH+cH²+dH³( a, b, c, d are constants).(3) The variation of structure of drifting sand flux in horizontal direction: the wind-blown mass totalQ(Q_total)will increase along the wind direction with the extension of the block length (L) in the height of 0-60cm, and it becomes stable after a certain distance and reaches saturation, and thus the relationship between the saturation capacity of soil erosion of stubble ground along the main wind direction and the length of the saturation path is in line with the cubic polynomialQtotal=a+bL+cL²+dL³ (a, b, c, d are constants); the length of the saturation path of the structure of drifting sand flux is closely related to wind speed, surface roughness of farmland, an the length of the block, and generally, the lighter the wind is and the rougher the surface is, the shorter the saturation path of the structure of drifting sand flux is with the extension of the block length, the longer on the contrary; the volatility of wind-blown mass of structure of drifting sand flux is high along the wind direction at 0- 30cm sand layer, but is low at 30-60cm and will be stable after a short distance, which because erosions at 0-30cm are mainly saltating particles and strongly affected by the turbulence effect, thus Structure of drifting sand flux is unstable and is not saturated, and Wind-blown mass will continuously increase; erosions at 30-60cm are mainly suspended particles, and erosion gravity and air suspension force tend to a balance after a shorter path, and then the structure of drifting sand flux will be saturated.(4) Wind strength of farmland erosion (Q_t) is negatively correlated with surface roughness, and is positively correlated with wind speed. Thus we established a model between wind speed (V) and wind strength—Q_t=a·exp(b·V) (a, b are constants.)...