The Soil Properties And Characteristics Of Water And Soil Loss Of Eucalypt Plantation In The South Of Guangxi

Eucalyptus is one of the most important plantation species in Guangxi. It has played an important role in relieving contradiction between wood supply and demand and expressing carbon sequestration efficiency of forest. However, with the increasingly area of eucalypt plantation, ecology problems caused by it have been given more focus. Therefore, in order to realize soil properties and the feature of water and soil loss in eucalypt plantation, and offer a reference for its sustainable management, this paper chose shrub and grass plot which had the same restore session as a comparison, pilot study and investigation have been conducted to eucalypt plantation aged1～3years in the south of Guangxi, five aspects have been explored, including the soil properties, the characteristics and dynamic of water and soil loss, the correlation between impact factors and soil erosion and its function model. The investigation result showed that:(1) The forest land was heavy clay soil, unit weight was between1.28and1.39g·cm-3, acidic and pH<5, the annual variation of unit weight and pH were not obvious. With the increasingly forest age, soil organic content, porosity, permeability and water-holding capacity were gradually increasing. With the increasingly soil depth and soil bulk density, the organic content, porosity and water-holding capacity were decreasing little by little. The nutrient pattern is different and its content has changed over time in allopelagic soil layer.(2) Critical rate of rainfall, the minimum rainfall causing runoff, was increasing with years, and the eucalyptus forest land of which is greater than shrub and grass plot, The surface runoff was largely caused by the rainfall over heavy rain, and the runoff coefficient increased with the increasing rainfall level. The monthly changes of surface runoff, soil loss, nutrient loss and rainfall were basically consistent, and the yearly changes of first3items were quite similar.(3) Among organic matter, Nitrogen, Phosphorus and Potassium, the first two were mainly losing with runoff, while the latter two were mainly losing with sediment; the size of the loss was organic matter>Potassium>Nitrogen>Phosphorus.(4) The following indexes in biomass and soil property had significant negative correlation with water and soil loss:litter biomass, radicula biomass, branches and leaves biomass, noncapillary porosity and permeability.(5) Surface runoff and soil loss have significant quadratic parabolic relationship with rainfall; Surface runoff and soil loss have the same relation and the rainfall and nutrient loss haven’t obvious correlation, which indicates that the forming process of nutrient loss is relatively complicated.(6) Water and soil loss were most serious, then quickly reduced, every index was reduced more than65%compared with the first year after eucalypt plantation was made. Comparing with shrub and grass plot which was naturally restored, eucalypt plantation aged1～3years had better effect of preventing surface runoff.