| The region of Mollisols in Northeast China is very important to the grain productivity.The Mollisols is known as "the giant panda of cultivated land".However,Mollisols erosion has seriously threatened the sustainable development of agriculture.Studies on splash erosion characteristics can reveal and reflect splash erosion mechanism.However,most current studies on splash erosion were conducted on non-ridge slope;little information is available on the up-down ridged slope,especially for the distribution of soil wat er stable aggregates during splash erosion process in the typical black soil region of Northeast China.Therefore,an in-situ field simulated rainfall experiment was conducted to investigate the effects of rainfall and slope gradient on the characteristics of splash erosion,the distribution of soil water stable aggregates and characteristic indices of soil aggregate in the process of splash erosion.Three rainfall intensities(30,60 and 90 mm/h)of representative erosive rainfall,two slope gradients(5° and10°)and two interval rain events(24 h intervals)were set,all treatments were replicated thrice.The main results were as follows:(1)The average splash erosion and total splash erosion all were increased with the increase of rainfall intensity and slope gradient.The influence of rainfall intensity on splash erosion was greater than that of slope under this test condition.At the same slope,as rainfall intensity increased from 30 mm/h to 90 mm/h,the total splash erosion was increased by 2.5 to 17.9 times.The total splash erosion of the second rainfall event is less than that of the first rainfall event.At the same rainfall intensity,as slope gradient increased from 3° to 5°,the total splash erosion significantly was increased by 30.52%～74.08%.The relationship between splash erosion with rainfall intensity and slope gradient could be expressed as a power function.Therefore,the land cover should be strengthened to eliminate raindrop impact in the fallow period of farming.(2)At rainfall intensities of 30 and 60 mm/h,splash erosion rate first decreased,then gradually reached to a steady state.At rainfall intensity of 90 mm/h,splash erosion rate first increased to the maximum value,then decreased,and finally reached t o a steady state.At rainfall intensity of 90 mm/h,the total splash erosion rate of Mollisols increased with the slope gradient increasing for the same rainfall duration.(3)The <1 mm soil aggregates were the main aggregate size fraction detached by rai ndrop splash,which accounted for 79.01% of total splash erosion;among which,the proportion of0.5-1 mm soil aggregates were the most,accounting for 32.94% of total splash erosion,while the proportion of 2-5 mm soil aggregates was the least,accounting for 3.36% of total splash erosion.However,>0.5 mm aggregate did not migrate.At the slope gradient of 3°,the transport capacity of 2-5 mm soil aggregates was increased with the increase of rainfall times;at the slope gradient of 5°,with the increase of rainfall times,the 0.25-0.5 mm soil aggregates showed an increasing trend.At rainfall intensity of 90mm/h,with the slope increasing,the 0.25-0.5 and<0.25 mm soil aggregates showed a decreasing trend,while the 2-5 and 1-2 mm soil aggregates showed an increasing trend.In conclusion,raindrop impact and runoff transport have significant effects on the separation and transport of black soil aggregates with different particle sizes.(4)At rainfall intensities of 30 and 60mm/h,the <2 mm and <0.25 mm soil aggregates reached to the steady state at the end of rainfall,respectively;the proportion of micro aggregates first increased and then reached a relatively stable stage.At rainfall intensity of 90mm/h,the 1-5mm and <0.25 mm soil aggregates showed the liner trend,and the proportion of micro aggregates showed a decrease trend.When the rainfall intensity increased from 30 mm/h to 90mm/h,the time for the proportion of microaggregates transported by splashing erosion to reach stability advanced from 40 min to 24 min.At rainfall intensity of 90mm/h,when the slope increased from 3° to 5°,the 0.5-1 mm soil aggregates showed a increased trend.(5)With the increase of rainfall intensity,slope gradient and rainfall times,the mean weight diameter and geometric mean diameter of splash-separated aggregates were increased.However,the mean weight soil specific area and fractal dimension were decreased.At rainfall intensities of 30 and 60 mm/h,with the increase of rainfall duration,the MWD and GMD of splash-separated aggregates presented a "double peak" distribution,the MWSSA and D of splash-sorted aggregates showed a trend of decreasing first and then reached to a steady state.At rainfall intensity of 90 mm/h,with the increase of rainfall duration,the MWD and GMD of splash-separated aggregates showed a fluctuating trend of increase,while the MWSSA and D of splash-sorted aggregates showed a fluctuating trend of decrease. |
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