| The Mianyang river basin is one of the key construction areas of the protection forest in the middle and upper reaches of the Yangtze River. The natural forest and plantations of basin are operated for soil and water conservation, windbreak and sand fixation, water conservation, climate regulation, pollution reduction. However, as time goes by, the human society has been developing continuously and people's living standard has been improved, the protection forest of the Yangtze River can not meet the needs of the development of the current situation. The forest has a single species, more pure forest plantation, planting density, thinning the lack of these problems.Natural regeneration of forest was poor, and the coverage rate of shrub and grass was low, and the soil stability was poor, which resulted in the decline of soil fertility and the difference of soil and water conservation benefit. Soil aggregate can be used to reflect the soil fertility, on the other hand, it can be used as a key indicator to measure the quality of the soil. Through the study of the main forest stand types, the distribution characteristics, the stability and the change of the fractal dimension can be used to reflect the soil structure of each stand. It can provide an important theoretical basis for the management and ecological construction of protective forest. Guansi River main forest types with pine and cypress oak mixed forest, pine and cypress, mixed forest, cypress tree mixed forest, pure forest of cypress, Eucalyptus grandis pure forest.In this paper, we studied the characteristics of soil aggregate in 5 forest types, including large aggregate distribution, micro aggregate distribution, aggregate stability, fractal dimension and so on. The results are as follows:(1)In the aggregate, the content of>5mm was the highest, which was 82.774% to 65.725, and the content of>0.25mm was 93.525% to 98.310%, Particle size decreases with decreasing particle size. There were differences in the content of aggregate in each stand. The content of large aggregate in the pine oak mixed forest is the most, Tung cypress mixed forest and pure forest of cypress large aggregates were less.(2)The content of water stable aggregate is mainly>2mm, the percentage is 30.18-84.172%, the percentage of>0.25mm particle size is 69.455?92.008%, After wet sieving, The large aggregates part disintegrated into aggregates of small size, but the water stable aggregates still occupy the main part, And the content of water stable aggregate in the mixed forest was more than that in the pure forest.(3)The characteristic micro aggregate ratio of the pine oak mixed forest is the most, Pine mixed forest was the lowest, The pine oak mixed forest microaggregates structure damage, Fertility begins to decline, can not play a very good protect water and fertilizer effect,it need to strengthen management, The mixed forest of pine and cypress dispersion coefficient and dispersion rate lowest, reunion, reunion with maximum degree, pine and cypress mixed forest soil structure, micro aggregate stability better, soil anti erosion ability strong in other vegetation.(4)The MWD and GMD sizes of water stable aggregates were measured by wet sieving method to characterize the soil structure. MWD and GMD showed that the mixed forest was greater than that of the pure forest, pine and cypress mixed forest soil aggregate is the best, In addition, the PAD and ELT of water stable aggregates and the soil K value showed that the mixed forest was lower than that of the pure forest.(5)Fractal dimension of water stable aggregates:Pine mixed forest< The pine oak mixed forest< Tung cypress mixed forest< Funebris forest< Eucalyptus grandis plantations, Because of the multi level structure and the composition and distribution of the stand biomass, the mixed stand has a more reasonable structure. Therefore, the D value is small. The cypress pure forest and Eucalyptus grandis plantations D value and larger relative to the mixed forest view aggregate instability, The destruction of soil structure is the most serious, and the loss of soil and water loss is easy to occur, and the transformation of pure forest is necessary.(6)The indexes of pure eucalyptus forest showed that the stability of water stable aggregates was significantly weaker than that of other vegetation. Compared with other forest stands, the aggregate of the soil aggregates in the pure forest was the worst. Aggregate stability is low, weak, it needs to carry on the transformation of business model.Growing fruits and grains can improve soil quality. |
PDF Full Text Request