| Purple soil is an important resourceof cultivated land in the Three GorgesReservoir Area，and slope cultivated land is the main form, with78%of the totalcultivated land area. As the structure of purple soil is characterized by large porosity,shallow soil, high infiltration capacity, and weak underlying shale permeability,interflow is widespread in purple soil area. Unlike many areas, nutrient leachingloss along the interflow plays an important role. Study on the Three GorgesReservoir dissolved nutrient leaching has important significance for the management ofsoil nutrient loss and water environment protection. Effectss of nitrate leachingconditions of slope cropland of purple soil in different rainfall intensity, slope, upsloperunoff and fertilization measures were examined by using two approaches, experimentsand software simulation. The main conclusion as following:The time of interflow occuring correlation with rainfall intensity is positivelyrelationship, with the increase of rainfall intensity, interflow occurrence of eachpositions of slope farmland has advanced. Generally speaking subsurface flow of eachposition of slope farmland has the relationship: downstream> midstream> upstream,and when rainfall intensity is small-scale, upstream may not occur. The nitrate-Nconcentration in interflow in the purple soil did not increase with the rainfall intensity,rather, strong rain dilutes the concentration of nitrate leaching. The nitrate leaching ofslope purple soil potential proportion relationship in small rainfall intensity is:downstream> midstream> upstream. In the storm condition, downstream was inhibited,and nitrate nitrogen leaching in the position of slope accounts for the main part of thewhole slope nutrient leaching.Unlike the role of rain intensity, slope increased only changes the moisturedistribution in soil ratio, does not make the soil abortion hydrograph obvious fluctuation.Nitrate leaching in down-slope position has been reduced with the increase of the slope,and the mid-slope position, up-slope position leaching increased first, then decreased.There exists a critical slope gradient, the mid-slope, up-slope position of nitrate leachingin slope as a maximum of15°.Runoff from upslope can promote the interflow，with the increase of upslope runoff,subsurface flow of each position of slope farmland has gradually increased and thedifference of runoff position in each slope position gradually reduced. A similar effect with slope factors, nitrogen leaching in different slope position is different. Nitrateleaching in down-slope position has been reduced with the increase of upslope runoff,and the mid-slope position, up-slope position leaching increased first, then decreased.Nitrate leaching of midlle-slope position and up-slope position reached the maximum,when upslope runoff was400ml/min and600ml/min, respectively.On the basis of experimental research，the simulation studies about fertilizationmethod influence on interflow and nitrate leaching of slope cropland of purple soil haveshown that: Under different fertilization methods, nitrate leaching in the soil althoughsomewhat different, but nitrate migration has the similar trends.As the nitrate migratingto deep soil layers, it also migrates along the slope downward, and soil nitrate nitrogentransport faster than non tillage layer. Under the same fertilization(150kg/m2), tillagelayer of nitrate nitrogen concentration was maintained at0.155~0.16kg/m3of surfacefertilization, while nitrate nitrogen concentration was maintained at0.08~0.105kg/m3of the base hole fertilization. Nitrate leaching of base fertilizater spot application to thenon-farming was more than the surface fertilization. Under different fertilization modes,nitrate leaching concentration of each slope position of typical points to reach themaximum in the middle of rainfall. Surface slope fertilizer nitrate leachingconcentration at each position in the rain35min to reach the maximum of0.2216kg/m3,while the base points fertilizer leaching concentration maximum at around27min, to0.188kg/m3. |
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