The Mechanism Of Runoff Generation And Characteristics Of Moisture Changing Process Of Slope Farming Purple Soil

Purple soil classified as Regosols in FAO soil taxonomy and Pup-Cambols in china soil taxonomy, is one of well known soil types with the particularities such as weathering easily, high natural fertility, etc., and feeding population of 500/km2. However, it often meets the water disasters (sporadic flooding and serious seasonal drought). For this reason, our objective is the research of the mechanism of runoff generation and characteristics of moisture changing process of slope farming purple soil, accordding to the theory of hydrology and the intergrated-means of compined the hydrology with the peodology, because it is the basis of the studies: soil erosion and protection, farming-land water balance, Non-point pollute, etc., and the direction gist of runoff arrange implement, solving water hazard and management of irrigation and fertilizer. And the major results and some new viewpoints were presented as follow:1) Sediment content of CN tillage system in runoff process is substantially low compared to ST under rainfall with high intensity, showing CN bear the efficient capacity of control soil loss. Nevertheless, when soil is saturated, the runoff intensity of both tillage systems is near, implicating CN has the limited function of reducing runoff.2) Based on the case analysis of observed all rainfall-runoff generation processes, A) the initiation time hysteresis of surface runoff generation isnotable when rainfall fall upon the unsaturated purple soils, which is attributed to the property of rapid water sorption and much non-capillary porosity. When soil antecedent condition is dry and the initial rainfall intensity is high, peak surface runoff also considerably lag behind that of rainfall, because of the formation of temporary relative impermeable top layer; B) Surface runoff is controlled primarily by infiltration-excess runoff mechanism under unsaturated condition; the major fraction of surface runoff are dominated by saturated infiltration-excess runoff response, only a small fraction by return flow mechanism when soil is saturated; C) Subsurface flow is dominated by saturated runoff mechanism, and the duration of subsurface post the rainfall end is dependent upon rather the soil properties than the rainfall characteristics; D) Subsurface flow intensity in cultivated soil layer (0~20cm) is high up to 35mm/h when rainfall intensity is up to 120mm/h, indicating the existing of macropores and pipe flow in cultivated layer. Therefore, throughflow rate is, in somewhat, rely upon the intensity of rainfall.3) The moisture changing processes at various location of a slope purple soil are obvious different: at up-location, soil moisture reduce more rapidly, therefore, drought will easily response to it at which the principle of often and little irrigation should be adopted. After a rainfall end, soil moisture content of cultivated layer is nearly stable within a certain period that is one week if rainfall leads to saturated runoff generation and is the optimal duration of fertilization. And we found the model of moisture changing is "reduction---stabilization---reduction" while the former researchers' result is linearly reduction or reduction after a steady period.4) Numerical simulation running of surface runoff shows simulation results presented the general features of surface runoff generation, and certain efficiency. After adjusting the input parameters, the simulation results show a good meet to the observed data. The numerical simulation of moisture varying processes have not shown a good fit to the measured, showing amoisture varying model of simple reduction, and not revealed the distinct courses at various slope locations. However, after simulating by the selected parameters shown the difference between various slope locations, the the coefficient of efficacy (CE) was increased obviusly and reached over 0.6, that is to say, the simualted results is reliable in a certain. These results prompt us the satisfied fit simulation can be reached only when we scientifically tre...