| Soil erosion is considered to be one of the most serious environmental problems in the world.Soil erosion causes land degradation and nutrient loss,which seriously restricts human survival and economic development.Rainfall splash erosion occurs in the initial stage of water erosion,resulting in the fragmentation of soil aggregates,and the blockage of soil pores,reduce water infiltration,so that a large number of small particles are denuded and transported.Therefore,soil erosion is an important issue that must be considered first to solve water and soil loss and prevent soil erosion.In the Mollisol region of Northeast China,there is a vast territory,fertile land,and a high degree of resource utilization.It is famous as the"Northeast granary".However,in the new century,with the continuous reclamation of a large number of wastelands,the soil structure has been severely damaged,and the decomposition of organic matter has been accelerated,these making soil aggregates more obvious.This makes the soil erosion resistance weak in the black soil area,and soil erosion is becoming more and more serious.Even the black soil layer in some areas has disappeared,revealing the loess,the so-called"cracked soil"phenomenon.At present,a large number of studies have been conducted on the soil erosion status of the black soil area in China,but they are all based on the impact of external forces on the aggregates.In fact,the impact force produced by raindrops is only about 1-3 atm,and whether this weak force can directly lead to the breakdown of the aggregate remains to be further explored.And the maximum does not exceed 10 atm,but the soil internal forces can be as high as thousands of atmospheres.Therefore,the external force is much smaller than the soil internal force on the aggregates.Therefore,this study adopts a self-made needle-type rainfall device,it uses 5 kinds of different electrolyte concentrations as rainfall solutions to simulate different degrees of internal force,and we were selected two typical black soils,Keshan black soil and Binxian black soil to make saturated samples of<5 mm.One part is used for simulating rainfall experiments,and the total losses were collected every four minutes for a total of 100 minutes of rainfall;the others were used for soil splash erosion experiments,and particle size screening of splash aggregates at different distances is carried out.research shows:（1）The magnitude and distribution characteristics of the soil internal forces in two typical black soils and the effect of soil internal forces on the aggregates stability were quantitatively obtained.When the electrolyte concentration was 1 mol·L-1,the soil internal force between soil particles appears as attractive force,while the other electrolyte concentrations are all repulsive forces,it make the aggregates are more unstable.When the electrolyte concentration is less than 10-2 mol·L-1,the repulsive force between soil particles gradually increases.At the same time,the mean weight diameter of soil aggregates is gradually decreasing,and the aggregates to breakdown more obviously;when the electrolyte concentration is greater than10-2 mol·L-1,the net force between soil particles remained keept the stable,and the mean weight diameter of aggregates changed to a small degree,which confirmed each other.It shows that under certain conditions,the electrolyte concentration of 10-2 mol·L-1 is the critical concentration value that affects soil internal forces distribution and the aggregates stability.（2）It was clarified that the fragmentation rules and migration characteristics of two typical black soil aggregates.With the electrolyte concentration decreased,the net force between soil particles increases rapidly,the aggregates were breakdown significantly,and the amount of soil splash erosion gradually increased,and the electrolyte concentration 10-2 mol·L-1 is the critical concentration value that affects the amount of splash erosion.With the increase of the splash distance,the amount of splash erosion of Keshan black soil and Binxian black soil both gradually decreased.The spatial distribution of splash particles is mainly at 0-10 cm and 10-20 cm,respectively.It accounts for 57.8-71.2%and 16.3-23.0%of the total amount of splash erosion;when the two black soil aggregates breakdown,the micro aggregates are mainly distributed in<0.053 mm,and the variation range is 47.3-78.6%;from the law of particle size distribution It can be seen that when the electrolyte concentration increased,the percentage of microaggregates of<0.053 mm decreased,while the percentage of aggregates of 1 to 0.5 mm and 0.25 to 0.5 mm gradually increased;under the same experimental conditions,the amount of soil splash erosion of Keshan black soil is larger than Binxian.It indicated that the erosion resistance of Keshan black soil is stronger than the Binxian black soil.（3）Explore the changes of soil cumulative loss under the different soil internal forces.With the electrolyte concentration decreased,the soil net force increased,it result in the aggregates were brokedown significantly,and the soil cumulative loss increased.The electrolyte concentration 10-2 mol·L-1 is the critical concentration value that affects the soil cumulative loss.It showed a good linear relationship between the mean weight diameter and the soil cumulative loss.Because the cumulative loss increased to varying degrees,it indicated that the soil cumulative loss will also be affected by the raindrop impact forces.Through the correlation analysis about soil cumulative loss with aggregate particle size content at each level showed that the soil cumulative loss of Keshan black soil and Binxian black soil are significantly positively correlated with microaggregates<0.053 mm,which indicated that the soil cumulative loss of the two soils depends on the content of microaggregates<0.053 mm.And the Binxian black soil has a larger cumulative loss than Keshan black soil,it indicated that the stability of Keshan black soil aggregates is stronger than that of Binxian black soil.This research result is consistent with the above study. |
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