Study On The Change Of Soil Particle And Loss Of Nutrient Based On Rainfall Simulator

Soil erosion and loss of nutrient which are caused by rainfall is one of the most serious environmental problems in China.Rainfall is not only the main factor of soil erosion,but also is the origin of runoff.Lots of soil particle which haw large amount of nutrient is transferred by runoff, and this action changes the structure and texture of soil,and also leads the re-allocation of nutrient. In order to overcome the limitation of rainfall data collection and the disturbing of natural factor,we analyises the relationship between the soil erosion,loss of nutrient and the character of rainfall which is produced by using the Norton VeeJetSO100 rainfall simulator,and the results as follows:(1) With the decreasing of nozzle's sweeping frequency,the values of rainfall factors inclusing the intensity of rainfall,precipitation and rainfall erosivity will decrease too.The character of rainfall factors'(intensity of rainfall,precipitation and rainfall erosivity) space distribution under the single nozzle condition as this:the max value of rainfall factor is in the nozzle's projective point,the more distance with the position of nozzle's projective point,the fewer value of the rainfall factor.And during the whole rainfall process,the relationship between the values of rainfall factors in control points(Y) and the distance with the nozzle's projective point(X) is this:Y=AX²+BX+C,(A,B,C are constants),so the character of rainfall factors'distribution is the distribution of quadratic curve.(2) In order to estimate the sizes of raindrops which are produced by using rainfall simulator under the condition of nozzle's different sweeping frequencies,we use the A.B.Best raindrop empirical equation to estimate.The relationship between intensity of rainfall and C₁,C₂ as this: C₁=AI^x,C₂= BI^Y(A,B are constants;C₁,C₂ are the parameters ofraindrop's size;0＜x＜1,-1＜y＜0), The range of raindrop's volume median diameter change is from 3.49mm to 7.35mm under the nozzle's different sweeping frequencies.With the increasing of nozzle's sweeping frequency,the numbers of raindrops increase,and also the raindrop's max diameter and min diameter increase,and the number percent of big raindrops increase at first and then decrease.Finally according to the rainfall simulator's working stability,the nozzle's sweeping frequencies are classified three kinds, such as low sweeping frequency(1-double,2-double),steady sweeping frequency(3-double),high sweeping frequency(4-double,5-double).(3) According to the results of rainfall experiment,we find that the action of rainfall factors which are produced by using rainfall simulator will lead to the change of soil particle.And the change of soil particle will lead to the change of soil structure and soil texture.The measurement indexes of soil particle's change include soil mechanical composition and soil fractal dimension.The experimental results show that:the change of soil mechanical composition-the amount of two kinds of sand,which the particle size range from 1mm to 0.25mm and from 0.25mm to 0.05mm, both increase during the rainfall process.And also the incrase rate in the top slope is faster than the bottom slope;the amount percentage of another two kinds of grain,which the.particle size range from 0.05mm to 0.01mm and from 0.01mm to 0.005mm,both increase in the top slope and decrease in the bottom slope.The amount percentage of clay obviously decreases during the rainfall process. The amount percentage of top slope's clay decreases to 25.13%when the nozzle's sweeping is in high sweeping frequency condition.And the amount percentage of bottom slope clay decreases to 7.33%,5.05%,5.65%,1.13%during the four different rainfall time intervals.In the whole rainfall process,with the increasing of intensity of rainfall,precipitation and rainfall erosivity,the soil fractal dimension increases.And the rainfall erosivity has the deepest influence to the change of soil fractal dimension.(4) The change of soil structure depends on the change of soil aggregate structure and the degree of soil aggregate structure dispersion.During the rainfall process,the order of the amount percentage of soil aggregate based on the method of dry sieving from the most to the fewest is that:＞2mm soil aggregate,2mm～1mm soil aggregate,1mm～0.5mm soil aggregate,0.5mm～0.25mm soil aggregate and＜0.25mm soil aggregate;And during the rainfall process the amount percentage of＜0.25mm soil aggregate based on the method of wet sieving is the highest in the other four kinds of soil aggregate,and with the extended of rainfall duration,the percentage increases.Because of the accumulation of rainfall's energy in the soil particle,the soil aggregate structure dispersions of＞0.25mm soil aggregate(P_0.25) and＞2mm soil aggregate(P₂) also increase.And in condition of the nozzle's same sweeping frequency,the P_0.25 of top slope is more than P₂ of bottom slope.Comparing to the actions of rainfall factors to the change of soil structure and soil texture and the erosion amount,we fred that rainfall erosivity has the deepest influence to the soil particle's change;the precipitation and intensity of rainfall have less influence.(5) The re-distribution actions of simulator rainfall to the surface soil nutrient include three ways,the loss of surface soil nutrient,the loss of sediment-runoff nutrient and the loss of runoff nutrient.During the rainfall process,the loss of surface soil nutrient in the whole slope decreases, and also during the condition of nozzle's high and steady sweeping frequencies,the loss rate of surface soil nutrient in the top slope is higher than in the bottom slope.The differences of soil organic matter,total nitrogen,available nitrogen,total phosphorus,available phosphorus,total kalium,available kalium in top slope and bottom slope reache to 1.30g/kg,0.08g/kg,5.57mg/kg,0.08g/kg,3.60mg/kg,0.08g/kg and 3.23mg/kg accordingly.In the three rainfall factors,the rainfall erosivity has the deepest influence to the loss of total nitrogen,total phosphorus and total kalium. And the loss of total kalium was deepesfly influenced by the three rainfall factors.The intensity of sensitivity of soil organic matter and other three kinds of available nutrients to the rainfall factors from highest to lowest is that:toil organic n'tatter＞available kalium＞available nitrogen＞available phosphorus.(6) During the rainfall process,the loss of sediment nutrient and the amount of runoff decrease in the condition of single nozzle's different sweeping frequencies.The experimental results show that the degree of decreasing amount of sediment nutrient's loss and runoff's loss in the condition of single nozzle's high and steady sweeping frequency is higher than the condition of low sweeping frequency.And the enrichment rate of nutrient increases in the whole rainfall process.The average value of enrichment rate of all kinds of nutrient from most to less is that:total nitrogen＞soil organic matter＞total kalium＞total phosphorus＞available nitrogen＞total phosphorus＞available phosphorus= available kalium.But in the runoff,the range of TN's change is wider than TP's,based on correlation analysis shows that the TN in the runoff has more close relationship with three rainfall factors than the TP.Only the average intensity of rainfall has some relationship with the amount of TP in runoff.