| The environmental issues have been arisen broad attention, while the soil erosion is one of the global environment problems. Soil erosion is the main cause the degeneration and loss of land source, which is an kind of natural disaster to restrict the human survival and the development for today's global environment. By the methods of field investigation and laboratory analysis, change characteristics of soil anti-erodibility, soil anti-scourability, soil erodibility and their influence factors were studied under different vegetations in dry valley and montane forest at the upstream of Minjiang River. The study is not only the need of ecology construction, but also it is the important contents of soil erosion. At the same time, the study would help to reveal the essence of soil erosion and provide theoretical basis for the ecology construction and conversion of farmland to forestry.1.Characteristics and influence factors of soil anti-erodibility under different vegetationsOn sunny slopes, soil anti-erodibility was the strongest for the conversion of farmland to Minjiang cypress, followed Minjiang young cypress and natural secondary forests. However, soil anti-erodibility was the poorest for the Robinia pseudoacacia. Soil anti-erodibility of 0-1 Ocm layer was higher than that of 10-20 cm layer. At the same time, there were significant difference among the index of soil anti-erodibility in the 0-10 cm and 10-20 cm layer under the different vegetations. On shady slopes, soil anti-erodibility was the strongest for the weed, followed the shrub and Minjiang young cypress. However, soil anti-erodibility was the poorest for the natural secondary forests.On sunny slopes, they were significantly negative correlation between sand fraction of mechanical composition and index of soil anti-erodibility, water stable index, aggregation degree in 0-10 cm layer. However, they were significantly positive correlation between physical clay and index of soil anti-erodibility, water stable index, structural granular index, aggregation degree. They were significantly positive correlation between medium-fine dust and water stable index, structural granular index. However, they were significantly negative correlation between medium-fine dust and soil dispersion coefficient. They were significantly negative correlation between<0.001mm content of micro-aggregate composition and index of soil anti-erodibility, they were significantly positive correlation between<0.001mm content of micro-aggregate composition and water stable index. In 10-20 cm layer, they were significantly negative correlation between sand fraction of mechanical composition and aggregation degree, physical clay, soil dispersion coefficient, however, they were significantly positive correlation between coarse dust of mechanical composition and aggregation degree. They were significantly positive correlation between physical clay of mechanical composition and aggregation degree, structural granular index. They were significantly negative correlation between content of at the size of 1-0.05mm in micro-aggregate composition and aggregation degree.On shady slopes, they were significantly negative correlation between sand fraction of mechanical composition and index of soil anti-erodibility, structural granular index, soil aggregation degree in 0-10 cm layer. However, they were significantly positive correlation between sand fraction of mechanical composition and soil dispersion coefficient. They were significantly positive correlation between coarse dust of mechanical composition and soil aggregation degree.They were significantly positive correlation between physical clay and structural granular index. They were also significantly positive correlation between medium-fine dust and index of soil anti-erodibility, water stable index, soil structural granular index. However, they were significantly negative correlation between medium-fine dust of mechanical composition and soil dispersion coefficient. In 0-10 cm layer, they were significantly positive correlation between content of at the size of 1-0.05 mm in micro-aggregate composition and soil dispersion coefficient, however, they were significantly negative correlation between content of at the size of 1-0.05mm in micro-aggregate composition and soil structural granular index. They were significantly negative correlation between content of at the size of<0.001 mm in micro-aggregate composition and index of soil anti-erodibility, water stable index, soil structural granular index,soil aggregation degree, however, they were significantly positive correlation between content of at the size of<0.001 mm in micro-aggregate composition and soil dispersion coefficient. In 10-20 cm layer, there were no significantly different between content of different particles and all indexes of soil anti-erodibilityfor the micro-aggregate composition and soil mechanical composition under different vegetations.On sunny slopes, they were significantly positive correlation between index of soil anti-erodibility, water stable index, structural granular index, soil aggregation degree and soil organic mater, content of soil total N in 0-10 cm layer, however, they were significantly negative correlation between water stable index structural granular index, soil aggregation degree and content of soil available K. They were significantly negative correlation netween soil dispersion coefficient and soil organic mater, content of total N, however, they were significantly negative correlation between soil dispersion coefficient and content of soil available K. In 10-20cm layer, they were significantly positive correlation between index of soil anti-erodibility, water stable index and soil organic mater. However, they were significantly negative correlation between water stable index, soil structural granular index and content of soil available K. They were also significantly positive correlation between soil dispersion coefficient and content of soil available K. However, there were no significant differences between soil aggregation degree and soil chemical properties.On shady slopes, they were significantly positive correlation between index of soil anti-erodibility, water stable index, structural granular index and soil organic mater in 0-10 cm layer. However, they were significantly negative correlation between index of soil anti-erodibility, water stable index, soil aggregation degree and content of soil available P. At the same time, they were significantly negative correlation between soil dispersion coefficient and soil organic mater. In 10-20cm layer, they were significantly positive correlation between index of soil anti-erodibility, water stable index and soil organic mater. However, they were significantly negative correlation between index of soil anti-erodibility, water stable index and content of soil available P.2. Relationships between soil erosion rate and soil physical properties in 0-10 cm layer under different vegetationsSoil erosion rates were from 21.34% to 60.51% under different vegetations, and the average value of soil erosion rate was 13.18%. Soil erosion rate of six vegetations had high proportions of>10%. The value of soil erosion rate was the lowest for the conversion of farmland to Minjiang cypress. However, the value of soil erosion rate was the highest for the Robinia pseudoacacia. These factors had the important effect on soil erosion rate, and these factors included soil organic mater, structure ped breaking ration aggregate mean weight diameter, geometric mean diameter and water stable aggregate of>0.25mm.3. Characteristics and influence factors of soil anti-scourability under different vegetations Changes of runoff amount were obvious with scouring time under different vegetations. Runoff amount was decrease after increase with the increasing of scouring time under different vegetations. Runoff amount of the control (CK) was lower than that of the shrub, and was higher than that of the other vegetations. Change amplitudes of runoff amount were the higher with the increasing of scouring time for the shrub and the control (CK). Change amplitudes of runoff amount were the lower with the increasing of scouring time for natural secondary forests and Minjiang young cypress. Sediment concentration was flat after decrease with the increasing of scouring time under different vegetations. Sediment concentration was the lowest with the increasing of scouring time for the conversion of farmland to Minjiang cypress. Sediment concentration was the lower with the increasing of scouring time for the mixed young stands, and the time of steady sediment concentration was later than that of the other vegetations.The results demonstrated that soil anti-scouring index changed in the following order of treatments: the conversion of farmland to Minjiang cypress> Minjiang young cypress> Robinia pseudoacacia> the shrub> the mixed young stands> the control (CK).Under different vegetations, they were significantly negative correlation between soil anti-scouring index and soil bulk density. They were significantly positive correlation between content of at the size of<0.001 mm in micro-aggregate composition and soil anti-scouring index. They were no significantly diffrent between content of the other particles in micro-aggregate composition and soil anti-scouring index. They were significantly negative correlation between content of soil available P and soil anti-scouring index. However, they were no significantly diffrent between soil anti-scouring index and soil organic mater, content of soil total N, content of soil available K.4. Characteristics and influence factors of soil erodibility under different vegetationsIn 0-10 cm layer, the results demonstrated that the value of soil erodibility(K) changed in the following order of treatments:Robinia pseudoacacia> mixed young stands>the shrub> Minjiang young cypress> natural secondary forests> the conversion of farmland to Minjiang cypress on sunny slopes under different vegetations. The results demonstrated that the value of soil erodibility(K) changed in the following order of treatments:natural secondary forests> the shrub>the weed> the conversion of farmland to Minjiang cypress on shady slopes under different vegetations. In 10-20cm layer, the results demonstrated that the value of soil erodibility(K) changed in the following order of treatments:Robinia pseudoacacia>mixed young stands>natural secondary forests> the conversion of farmland to Minjiang cypress> Minjiang young cypress>the shrub on sunny slopes under different vegetations.The results demonstrated that the value of soil erodibility(K) changed in the following order of treatments:the weed> natural secondary forests> Robinia pseudoacacia> Minjiang young cypress on shady slopes under different vegetations. They showed the same change between soil anti-scourability and soil erodibility under different vegetations. So, EPIC model was available for estimating soil erodibility in ecotone between dry valley and montane forest.In 0-10 cm layer, they were significantly negative correlation between soil erodibility and soil organic carbon, the content of soil total N, content of soil silt under different vegetations. However, they were significantly positive correlation between soil erodibility and content of soil sand under different vegetations. In 10-20 cm layer, they were significantly negative correlation between soil erodibility and soil organic carbon, the content of soil total N under different vegetations. However, they were significantly positive correlation between soil erodibility and content of soil silt under different vegetations. |
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