Detachment And Transport Characteristics Of Soil Aggregates By Raindrop Splash In The Noethern Loess Plateau

The Loess Plateau is the most serious area of soil erosion in China.The water erosion is the main way of soil erosion.And there are many reasons such as fragile ecological environment,loose soil structure,hilly and gully aspect,serious contradictory between man and land and unreasonable land development and utilization and so on to speed up the soil and water loss in the region,which seriously hindered the sustainable development of the region.The detachment and transport of soil aggregates,which result from raindrop splash,is the initial stage and an important step for water erosion.It provides a material basis for the subsequent erosion process,and is mainly determined by soil and rainfall properties.Different raindrops have different detachment and transport characteristics for different soil aggregates.Currently,the study of splashed aggregates spatial distribution is relatively weak in the typical soils of the Loess Plateau by raindrop.Therefore,the two typical soils(Loessial soil and Sandy loam soil)in the Loess Plateau are studied.Five raindrop diameters(2.67mm~4.05mm)were simulated to splash the in-situ soil of the tillage layer.Splash plates were used to collect the splashed aggregates at five distance intervals(0~10cm-40~50cm),and seven aggregate fractions were sieved.The characteristics of splash amount and the splashed aggregates size distribution and selectivity were comparatively analyzed under different raindrop diameters.The splash prediction model was constructed.And the raindrop diameter that made aggregates greatest degree destroyed was found.The main findings are as follows:(1)The total splash amount increased exponentially with increasing raindrop diameters under five different raindrop diameters for Loessial soil and Sandy loam soil(R2=0.971 and0.989,P<0.05).And the total splash amount of Sandy loam soil is larger than that of Loessial soil.There was no significant difference between the total splash amounts of the 2.76 mm raindrop diameter and 3.05 mm raindrop diameter,however there was significant difference between the total splash amounts of other raindrop diameters for Loessial soil(P<0.05).The loessial soil aggregates is more distant than the sandy loam aggregates.For the same splash distance,the splash amount increased exponentially with increasing raindrop diameter,and the difference between the splash amounts gradually increased.For the same raindrop diameter,the splash amount decreased linearly with increasing splash distance when theraindrop diameter was less than 3.39 mm for Loessial soil.However,the splash amount decreased exponentially with increasing splash distance at other raindrop diameters for two soils,and the difference between the splash amounts gradually decreased(P<0.05).(2)Based on the raindrop diameter d and splash distance S,the splash amount predicted model(M)is M=adbSc(R2>0.922,P<0.05).(3)The Loessial soil splashed aggregates were mainly distributed in<0.106 mmfragments,accounting for 94.085%~97.411% of the total splash amount.The Sandy loam soil splashed aggregates were mainly distributed in <0.25 mmfragments,with a range of 98.092% ~ 98.864%.And the mass percentage of main composed fraction of splashed aggregates is larger than that of two in-situ soils.For the Loessial soil,<0.053 mm aggregates were most likely to be transported by raindrops,and the mass percentage increased with increasing splash distance.For the Sandy loam soil,0.053~0.106 mm aggregates were the most likely to be transported by raindrops,and the mass percentage increased with increasing splash distance.(4)The destroyed degree of two soils aggregates increased first and then decreased with increasing raindrop diameter.The destroyed of Loessial soil aggregates and the Sandy loam soil aggregates is greatest when the raindrops were 3.375 mm and 3.488 mm respectively.And the destroyed degree of Loessial soil aggregates was higher than that of Sandy loam soil.For the Loessial soil,the splash distance had a great influence on the size distribution of splashed aggregates,and the change of the raindrop diameter in the same splash distance had little effect on the size distribution of splashed aggregates.(5)The ER values of >1mm aggregates were almost zero for two soils.For the Loessial soil,when the raindrop diameters were >2.67 mm,the ER values of 0.106~1mm aggregates were <1 at different splash distance.The ER values of 0.053 ~ 0.106 mm aggregates increased with increasing raindrop diameter.Under the five kinds of raindrops,<0.053 mm aggregates of different splash distance showed enrichment characteristics.For the Sandy loam soil,the ER values of 0.106~1mm aggregates were regularly changed with increasing raindrop diameter and splash distance.0.053~0.106 mm aggregates were most easily enriched,indicating that it could be preferentially transported by raindrops.The <0.053 mm aggregates were also easily transported,but the ER values were <1.