The Characteristic Of Soil Aggreage Detachment And Transportion By The Raindrop Splash Test

Splash erosion,which is a main dynamic for the detachment and transport of soil aggregates,is the initial stage of soil water erosion.Soil aggregate is a crucial indicator determining the plough layer soil fertility.Splash erosion not only broke the surface soil structure,but also created soil particles for the runoff which intensified soil and water loess,influenced the capacity of land production.Destruction of the plough layer aggregate has a negative effect on the content of soil available water and soil fertility,destroying the soil structure and restricting agricultural development of the Loess Plateau.Different raindrop diameter of rain influence the fragment characteristics of breakdown and transportion.Current research main focuses on the influence factors of splash erosion and previous research more confines to the single index to reflect the splash erosion rule,such as splash amount which ignores the space and particle size distribution characteristics of the splash fragments.Thus,the study used the self-designed raindrop generation device and six raindrop diameter(2.67 mm~5.45 mm)to carry out rainfall experiments on the surface layer of typical zonal soil(Loess,Darb soil and Dark loessial soil),and sieved the fragments for the different splash distance(0~50 cm).The study made the quantitative research about the quantity change and the spatial distribution characteristic of fragments under the different rainfall conditions.A model was obtained to predict the amounts of splash detachment.Predict whether there was a raindrop diameter which made the aggregate broken degree largest by comparing the aggregate characteristic parameters.we get the following conclusions:(1)The relationship between the amount of splash detachment and the raindrop diameter increased in a positive linear trend(R2=0.985,0.860 and 0.916,P<0.01)for Loess,Darb soil and Dark loessial soil,respectively.Total splash erosion mass of six raindrop diameters was mainly distributed at splash distance 0~20 cm for the three soils.(2)For the same splash distance,there was extremely significant linear relationship between the amount of splash erosion and the raindrop diameter(P<0.01).For the same soil,the growth rate of splash amount decreased with the increase of the splash distance.For the same raindrop diameter,the splash amount decreased exponentially with the splash distance increased for the three soils(P<0.01).(3)A model was obtained to predict the amounts of splash detachment(M)for the raindrop sizes(d)and distance of splash detachment(S):cb××=SdaM.The a,b and c were experience coefficients.(4)Overall,as the raindrop diameter increased,the content of water stable macroaggregates(>0.25 mm)presented the down-up trend for three soils.For <0.25 mm size fraction,the mass percentage presented a fluctuated improving trend with splash distance increasing,which showed >250 mm macroaggregates break into <0.25 mm microaggregates.(5)The mass percentage of 2~1 mm,1~0.5 mm,0.5~0.25 mm,0.25~0.106 mm and0.106~0.053 mm size firstly decreased and then increased with raindrop diameter increasing at the splash distance 0~10 cm and 10~20 cm.For the Loess,Darb soil and Dark loessial soil,the mass percentage of <0.053 mm size firstly increased and then decreased with raindrop diameter increasing.The mass percentage of 2~1 mm,1~0.5 mm,0.5~0.25 mm,0.25~0.106 mm and 0.106~0.053 mm size firstly decreased and then increased with raindrop diameter increasing at the splash distance 20~30 cm,30~40 cm and 40~50 cm.And the mass percentage of <0.053 mm size firstly increased and then decreased with raindrop diameter increasing.(6)The fractal dimension(D)and mean weight diameter(MWD)with raindrop diameter changed e vidently as quadratic function.For the Loess,Darb soil and Dark loessial soil,the maximal value of fractal dimension were 4.255,4.220 and 4.217 which made the aggregate broken degree largest,and the minimal value of mean weight diameter were 4.095,3.847 and4.016 which meant the aggregate stability lowest.Overall,raindrop diameter 2.67 mm was less than raindrop diameter 5.45 mm for the value of fractal dimension of three soils.(7)On the whole,the ER values increased gradually with the reduction of particle size for the three soils.The result confirmed that ER values for >1 mm fragments were close to 0for the Loess,Darb soil and Dark loessial soil.The ER values of raindrop diameter 2.67 mm had the maximum at 1~0.5 mm,0.5~0.25 mm,0.25~0.106 mm and 0.106~0.053 mm size fraction,for the Loess,Darb soil,respectively,which illustrated the delicate raindrop diameter made the aggregate damaged easily.For each raindrop diameter,ER values for 0.106~0.053 mm and <0.053 mm fragments were >1.For the three soils,splash erosion aggregate of particle size < 0.053 mm obtained minimum ER value at raindrop diameter 2.67 mm.