Aggregate Stability Of Lateritic Red Soil And Its Response To Rainfall Splash Erosion In South Subtropical Zone

The influence of soil erosion on global environment is becoming more and more serious.The red soil region of the south subtropical region has been facing the problems of soil erosion,fertility attenuation and soil erosion for a long time.The red soil region in the south subtropical is rich in hydrothermal conditions and is an important grain producing area.However,due to its high temperature,rainy climate environment and unreasonable land use,it has become one of the soil and water loss regions in China.Splash erosion occurs in the initial stage of soil erosion and is a process of surface soil particles breaking and transporting under the impact of raindrops,which provides material basis for the development of gully erosion and surface erosion.Therefore,this paper selected the latretic soil developed from sand shale and quaternary red clay as the research objects to study the characteristics of soil aggregates under land use patterns such as woodland,orchard and arable land.Soil physicochemical properties and aggregate stability were measured,and the spatter response characteristics of soil aggregates under four different rain intensities(30 mm/h,60 mm/h,90 mm/h and 120 mm/h)were studied by simulated rainfall.The main conclusions are as follows:(1)The parent material of quaternary red clay is viscous and heavy,with large soil volume and small porosity.The parent material of sand shale has smaller bulk density but larger porosity.The contents of organic matter,particulate organic carbon and mineral bound organic carbon in woodland were 1.12-1.61,1.58-7.67 and 0.89-1.44 times of that in orchard and arable land,respectively.(2)The internal friction angle and cohesion indexes of the two parent soils were as follows: quaternary red clay forest land(Q1)> sand shale forest land(S1)>sand shale orchard(S2)> quaternary red clay land(Q3)> quaternary red clay orchard(Q2)> sand shale land(S3).The mean weight diameter(MWD)and geometric mean diameter(GMD)of soil aggregates in Q1 were 2.16 mm and1.69 mm,1.91 mm and 1.45 mm,respectively,after dry and wet screening methods.The MWD and GMD values of S3 soil aggregates were 1.87 mm and 1.38 mm,1.12 mm and 0.81 mm,respectively.The contents of water-stable aggregate(WSA)in all soils were more than 83.38% after three treatments by LB method.The relative dissipation index(RSI)of S3 soil aggregates was the highest,indicating that S3 soil aggregates were most sensitive to dissipation.Q2 soil aggregate had the highest relative mechanical fragmentation index(RMI),indicating that it was most sensitive to mechanical fragmentation.(3)Soil aggregate stability was significantly positively correlated with organic matter and particulate organic carbon content(p<0.01),and with clay content(p<0.05);The soil shear strength(internal friction angle and cohesion)was positively correlated with organic matter and particulate organic carbon content(p<0.01).The contents of clay,organic matter and particulate organic carbon in soil have important effects on its stability.(4)The amount of soil aggregate spatter increases with the increase of rainfall intensity,and MWD is negatively correlated with the amount of soil aggregate spatter under different crushing mechanisms.The spattering amount of soil aggregates in forestland was the least,and the spattering amount of soil aggregates in orchard and arable land was 1.20-8.38 and 1.53-6.68 times of that in forestland,respectively.With the increase of rainfall intensity,the content of >2mm aggregate in spatter erosion soil showed an increasing trend,ranging from0.11% to 56.45%.The fractal dimension of spatter aggregates is negatively correlated with the contents of >2 mm and 2-1 mm aggregates,and positively correlated with the contents of 0.5-1 mm,0.25-0.5 mm and <0.25 mm aggregates.(5)The amount of soil aggregate spatter erosion in downslope is 3.85-30.44 times of that in upslope.The spatter within 0-10 cm accounted for 71.17%-89.32%of the total amount,and the farther the distance from the center,the less spatter.The mean weight distance(MWS)of spatter transport was Q1 correlation analysis showed that the stronger the stability of soil aggregates,the worse the dispersion ability of soil aggregates,and the less spatter erosion within each range.(6)The spatter erosion rate of soil aggregates increased firstly and then decreased with the increase of rainfall time.Under the rainfall intensity of 30～60mm/h,the soil reached the peak in 24～36 min.Under the rainfall intensity of90～120 mm/h,soil spatter erosion rate reached the peak within 12～30 min.The fractal dimension of spatter aggregates is high at the beginning of rainfall and tends to be stable with the increase of rainfall time.In the process of rainfall,the spatter rate of aggregates is negatively correlated with the fractal dimension,indicating that with the increase of spatter amount per unit time,the content of large particles in spatter size increases,while the content of small particles decreases.This study shows that the latretic soil in the south subtropical region is prone to spatter erosion under continuous rainfall conditions,and effective vegetation engineering measures should be taken,such as returning farmland to forest,compound farming,construction of horizontal ditch and fish scale to prevent and control soil erosion in this region.