| In recent years,with the enhancement of public environmental protection awareness and national attention to environmental pollution control,control of soil erosion is increasingly valued by all sectors of the society.Because of the weak corrosion resistance of purple soil,the distribution area undulates terribly,and it is located in the subtropical zone.In the case of strong rainfall,soil erosion can easily lead to soil nutrient loss,soil fertility and productivity decline,which affects the production and life of the local people.On the basis of summarizing the relevant research at home and abroad,this paper studied the purple soil under six vegetation cover?orchard,warm temperate coniferous forest,eucalyptus forest,shrub,coniferous and broad-leaved mixed forest,deciduous broad-leaved forest?in Mou Ding country.Physicochemical properties?including pH value,total P.available P,total N,available N,organic matter?of the purple soil under six vegetation cover and distribution characteristics of humus profile were studied.Taking the soil of orchard as an example,three different rainfall intensities were selected and the soil column simulation experiment was carried out in the room.It studied the dissolution characteristics of humus in water and the effects of different rainfall intensity on soil humus loss at different soil depths.The results were as follows:?1?The soil profiles were divided into litter layer,and 0-10cm,10-20cm and 20-30cm,soil samples were collected to study physicochemical properties of the purple soil under six vegetation cover and distribution characteristics of humus profile.The results showed that the total P?TP?,available P,total N?TP?,available N,organic matter.HS-C.HM-C.HA-C.FA-C of litter layer were significantly higher than those of other layers and they decreased with increasing soil depth.There were significant differences in the humus carbon content of the purple soil in the different coverage modes in Mou Ding.The average carbon content of humus in sequence from low to high is:eucalyptus forest<orchard<coniferous and broad-leaved forest<warm temperate coniferous forest<shrub<deciduous broad-leaved forest.Soil humus content and composition were closely related to the physicochemical properties of the soil.There was a significant positive correlation between each pair of humus,humic acid,fulvic acid and huenin?p<0.01?.At the same time,they were positively correlated with soil organic matter,TP,available P,TN and available N?p<0.05?.?2?The effects of soil erosion on humus dissolution under different rainfall conditions were studied by setting the rainfall intensity to 0.5 mm min-1,1 mm min-1 and 2 mm min-1.The results showed that the time of beginning to leak under the three kinds of rainfall intensity were 499,338 and 176 min,the total duration were 1639,1378 and 1088 min.The flow rate of the erosive liquid were 3.33,5.14 and 29 mL min-1,and the flow rate of the erosive liquid was 30,20,7 min,respectively,when the rainfall intensity was 0.5,1 and 2 mm min-1.which indicated that the rainfall intensity was greater,the sampling time spent less,the flow rate of the erosive liquid was faster.The total organic carbon,fulvic acid and humic acid showed the same dissolution law under different rainfall intensities,and presented that the trend first increased and then reduced,besides.the dissolution concentration also increased with the increase in rainfall intensity.When the rainfall intensity was 0.5 mm min-1,the maximum dissolved concentrations of total organic carbon,fulvic acid and humic acid respectively were 33.22 ± 1.97,22.98 ± 0.17and 6.78± 0.17 mg·L-1.When the rainfall intensity was 1 mm min-1,the maximum dissolved concentration of total organic carbon,fulvic acid and humic acid respectively were 68.89± 1.13,22.98± 0.19 and 8.52±0.23 mg·L-1.When the rainfall intensity was 2 mm·min-1,the maximum dissolution concentration of total organic carbon,fulvic acid and humic acid respectively were 82.42±0.76,37.64±0.]9,9.39±0.23 mg·L-1.The dissolution concentration of fulvic acid in water was greater than that of humic acid,because fulvic acid was more mobile in water than humic acid.There were some differences in the degree of humus loss under different rainfall intensities and soil depths in the study area.When the rainfall intensity was 2 mm·min-1,the loss of humus was most serious,next was when 1 mm·min-1,the weakest was when 0.5 mm·min-1.The degree of humus loss was most severe at soil depths of 0-10 cm,followed by soil depths of 10-20 cm,which is relatively weak at soil depths of 20-30 cm.Therefore,the reduction rate of humus increases as the increase of rainfall intensity,and decreases as the increase of soil depth.?3?Taking the orchard soil as an example,the distribution of soil aggregates at different depths was studied,and the erosion characteristics of cultivated soil was found.The fractal dimension of purple soil in the orchard ranged from 2.11 to 2.48,and the fractal dimension of soil aggregates in 0-10,10-20 and 20-30 cm was 2.48.2.26,2.11.The higher the content of aggregates?<0.25 mm?was,the higher the fractal dimension of soil aggregates was.The fractal dimension of aggregates decreased with the increase of soil depth,which indicated that the stability of soil structure was better with the increases of soil depth.The middle weight diameter?MWD?of dry sieving 0-10,10-20 and 20-30 cm aggregates respectively were 3.28±0.08,4.96±0.05,5.47±0.13 mm and the MWD of wet sieving 0-10,10-20 and 20-30 cm aggregates were 2.38±0.07,2.47±0.05,2.7±0.11 mm.The MWD of dry sieving aggregates was significantly higher than that of wet sieving aggregates,which indicated that the MWD of wet sieving aggregates could reflect the stability of soil structure.The MWD increased as the growth of soil depth,which indicated that the soil stability was better with the rise of soil depth.?4?Soil erosion control measures:for the forest land,the preservation of surface vegetation,vegetation coverage growth and rational use of space layout are effective methods to control soil erosion and nutrient runoff loss.To improve the orchard humus content,interplanting green manure,keeping the soil loose,opening a good ditch and the rational use of organic fertilizer are effective. |
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