Study On The Soil And Water Conservation Benefits Of Different Vegetation Coverage Patterns In Rainy Area Of West China

The Rainy Area of West China located in the transition zone of Sichuan basin and alpine and plateau of western Sichuan. Its special geographical position made the rainfall in this area was plentiful, and occupied an important position in whole ecological barrier construction of upper Yangtze River. Meanwhile, this area was also the key region of returning farmland to forest and grass in Sichuan province. On the condition of the special rainfall in this area, reasonable vegetation structure configuration in plantation management process played crucial roles on the protection of the ecology environment. This study set five kinds of vegetation coverage patterns, they were respectively waste grassland, Cryptomeria fortunei plantation without ground cover, Cryptomeria fortunei plantation with ground cover, Eucalyptus grandis plantation without ground cover, Eucalyptus grandis plantation with ground cover. In this research, the surface runoff, sediment loss, soluble nutrient loss characteristics, soil physical and chemical properties of five different kinds of vegetation coverage patterns were comparative analyzed to evaluate the benefit of soil and water conservation of different vegetation coverage patterns such as intercepting surface runoff, sediment loss, solubility nutrient loss and improving the soil physical and chemical properties.(1) The surface runoff and sediment yield characteristics of different vegetation coverage patternsFrom January to May and October to December in 2009, the runoff plots of each vegetation pattern did not generate surface runoff because the rainfall and rainfall intensity were small. From June to September in 2009, the runoff plots of each vegetation pattern generated surface runoff with the increasing of the rainfall and rainfall intensity, and the monthly runoff of different patterns showed as August>July>September>June, while the monthly sediment yield showed as July>August>September>June. The annual runoff of different patterns in 2009 showed as Cryptomeria fortunei plantation without ground cover>Eucalyptus grandis plantation without ground cover>Cryptomeria fortunei plantation with ground cover>Eucalyptus grandis plantation with ground cover>waste grassland, and the annual sediment yield presented as Eucalyptus grandis plantation without ground cover>Cryptomeria fortunei plantation without ground cover>Cryptomeria fortunei plantation with ground cover>waste grassland≈Eucalyptus grandis plantation with ground cover. The annual runoff and sediment yield of waste grassland were lowest than other patterns, that of Cryptomeria fortunei plantation and Eucalyptus grandis plantation without ground cover were highest, while that of two plantation patterns with ground cover were mediacy. The annual runoff of Cryptomeria fortunei plantation was higher than that of Eucalyptus grandis plantation inspite of ground cover. The annual sediment yield of Cryptomeria fortunei plantation with ground cover was higher than that of Eucalyptus grandis plantation with ground cover, while that of Eucalyptus grandis plantation without ground cover was higher than that of Cryptomeria fortunei plantation without ground cover.(2) The soluble nutrient loss characteristics of different vegetation coverage patternsThe water soluble nutrient (total soluble N, NO3--N, NH4+-N, soluble P, K+, total soluble C) loss amount were closely related to runoff. The soluble nutrient loss amount of waste grassland were lowest than other patterns, while that of plantation patterns without ground cover were highest, and that of plantation patterns with ground cover were between waste grassland and plantation patterns without ground cover. Except for NH4+-N, the soluble nutrient loss amount of Cryptomeria fortunei plantation were higher than that of Eucalyptus grandis plantation inspite of ground cover. Beside the NO3--N of Eucalyptus grandis plantation, remaining ground cover could obviously reduce the soluble nutrient loss amount of Cryptomeria fortunei plantation and Eucalyptus grandis plantation compared with the plantations without ground cover.(3) The soil physical properties of different vegetation coverage patternsCompared with removing ground cover, remaining ground cover could significantly reduce the soil bulk density of Cryptomeria fortunei plantation and Eucalyptus grandis plantation, improve the soil porosity and water retention of upper layer, but decrease the porosity and capillary water capacity of subsoil. The natural water content of grassland was highest, soil bulk density, soil porosity condition and water retention were between plantations with ground cover and without ground cover, while the soil porosity and water retention were lowest. The soil bulk density of Cryptomeria fortunei plantation was lower than that of Eucalyptus grandis plantation inspite of ground cover, but the soil natural water content and water retention of Cryptomeria fortunei plantation were higher than Eucalyptus grandis plantation.(4) The soil chemical properties of different vegetation coverage patternsIn every patterns, the content of soil organic matter, total N and total K of subsoil, soil microbial biomass C and microbial biomass N of upper layer and subsoil of grassland were highest than other patterns. The content of soil organic matter, total N of upper layer, hydrolysable N of upper layer and subsoil, the content of soil NO3--N and NH4+-N of subsoil of grassland were between plantation patterns with ground cover and without ground cover, and the soil pH value of upper layer and subsoil of grassland were between Cryptomeria fortunei plantation and Eucalyptus grandis plantation. While the content of soil total P, NO3--N, NH4+-N and soluble C of upper layer, the soil soluble N of upper layer and subsoil, the soil available P of subsoil of grassland were all lowest than other patterns.The results about the effect of ground cover on soil chemical properties of Cryptomeria fortunei plantation and Eucalyptus grandis plantation showed as follows. The content of soil organic matter, soluble C of upper layer of Cryptomeria fortunei plantation with ground cover, the soil microbial biomass C and microbial biomass N of upper layer of Eucalyptus grandis plantation with ground cover, the total N of subsoil, hydrolysable N and NH4+-N of upper layer and subsoil of Cryptomeria fortunei plantation and Eucalyptus grandis plantation with ground cover were all higher than that of plantations without ground cover. While the content of soil soluble N of upper layer of Eucalyptus grandis plantation without ground cover, the soil organic matter, soluble C and soluble N of subsoil, the soil total N of upper layer, the soil NO3--N of upper layer and subsoil of Cryptomeria fortunei plantation and Eucalyptus grandis plantation without ground cover were higher than that of plantations with ground cover.The comparison results of the soil chemical properties between Cryptomeria fortunei plantation and Eucalyptus grandis plantation showed that the content of soil total P and NO3--N of upper layer, the total N of subsoil, the soil microbial biomass C and microbial biomass N of upper layer and subsoil of Eucalyptus grandis plantation were all significantly higher than that of Cryptomeria fortunei plantation, but the content of soil organic matter, NH4+-N and pH value of upper layer and subsoil of Cryptomeria fortunei plantation were obviously higher than that of Eucalyptus grandis plantation.