Studies On The Soil Representative Biochemical Characteristics For Different Land Types In The Three Gorges Reservoir Area

There are very prominent contradictions between the population and land use in the Three Gorges Reservoir area, where unreasonable land using exists. The land use patterns lead to serious destroyed soil environment in the Three Gorges Reservoir area, especially the effects on soils.This research focuses on the five main land use patterns in the riverbank slopes of the Three Gorges Reservoir area (woodland, grassland, farmland, abandoned farmland, and hydro-fluctuation belt), studying the effects of different land use patterns on soil chemical properties, soil enzymes activities and soil microbial quantity in the riverbank slopes in the Three Gorges Reservoir area. Depanded on the results, deeper researches on hydro-fluctuation belt (grassland, farmland, and abandoned farmland) and sloping farmland (Citrus reticulata field, Zea mays field, Vicia faba field, and abandoned farmland) in the riverbank were made. This research is aiming at exploring adaptive land use pattern to the specific environment of the Three Gorges Reservoir area, and providing theory evidences for scientific land use and ecological restoration. The results show that:1. The effects of different land use patterns in the bankslope areas:(1) The quantity of three main microorganism types in soils followed:bacteria actinomycetes> fungi. The quantity of bacteria in woodland was the lowest among the five land use patterns, while the quantity of fungi in hydro-fluctuation belt was the lowest.(2) Woodland had the lowest content of soil total and available nitrogen, and soil total and available phosphorus, compared to those in other land use patterns respectivelys. Woodlandcan effectively reduce the nitrogen and phosphorus content in soil and hence decrease the input of nitrogen and phosphorus into the water body of the Three Gorges Reservoir. However, the content of soil available nitrogen, available phosphorus and total phosphorus in the hydro-fluctuation belt was the highest compared to those in other land use patterns respectively. The continuous agricultural farming in the hydro-fluctuation belt could be one of the crucial sources for inputting nitrogen and phosphorus into the water body of the reservoir, which may cause eutrophication.(3) The activity of soil catalase, urease and alkaline phosphatase in woodland was the lowest among all the land use patterns. In contrast, farmland had the lowest activity of soil invertase and protease. However, abandoned land had the highest activity of soil urease and protease, while grassland exhibited the highest activity of soil invertase and alkaline phosphatase.(4) The soil catalase and alkaline phosphatase activity presented significantly positive relationship with the content of soil total nitrogen, available nitrogen, total phosphorus, organic matter, and pH value respectively. In contrast, there was a significant negative correlation between soil alkaline phosphatase activity and available phosphorus content. The invertase and urease activity also showed significant correlations with soil total nitrogen, available nitrogen, available phosphorus and pH value respectively. In the meantime, significant correlation was detected not only between soil urease activity and organic matter content, but also between soil protease activity and total nitrogen, available nitrogen, and pH values respectively.2. The effects of different land use patterns in the hydro-fluctuation belt:(1) The contents of soil nitrogen, phosphorus, potassium, and organic matter and soil pH value regularly distributed in the three land use patterns and the two soil layers (0～10cm,10～20cm). In10～20cm soil layer, the organic matter content in grassland was significantly higher than that in abandoned farmland, while no significant difference was found among the three different land use types in0～10cm soil layer. However, the soil organic matter contents in the upper layer (0～10cm) was significantly higher than the lower layer (10～20cm) in grasslands and abandoned farmland.(2) There were significant differences in terms of soil enzymes activities in different land use patterns (p<0.05). In each land use pattern, the activities of soil enzymes were reduced with the increasing of soil depth, while there was no significant difference between the two soil layers in terms of soil protease and phosphatase activity (p>0.05).(3) Bacteria approximately accounted for90%among the three kinds of soil microbes, followed by actinomycetes and fungi. However, there were significant differences between land use patterns in terms of the numbers and compositions of diverse micro flora (p<0.05). Moreover, the number of soil microorganisms in topsoil (0～10cm) was higher than that in subsoil (10～20cm) under each land use pattern. (4) Analysis of correlation indicated that soil microbial quantities and soil enzyme activities under different land use patterns had correlationwith each other.3. The effects of different land use patterns in sloping farmland:(1) The soil available nitrogen content in sloping faemland in0～20cm soil layer was significantly higher than that in40-60cm soil layer, and the content of soil available nitrogen in Citrus reticulata field was significantly lower than that in abandoned farmland. The soil total phosphorus content was also decreased with the increasing of soil depth in each kind of land use pattern. In the0～20cm and20～40cm soil layer, the soil total phosphorus content in Citrus reticulata and Zea mays field was significantly higher than that in abandoned farmland respectively. The content of organic matter in the0～20cm soil layer of citrus reticulata was significantly higher than that in the lower soil layer. Moreover, in the0～20cm soil layer, the soil pH value was significantly different between citrus reticulata field and abandoned farmland, while there was significant difference between soil pH value in citrus reticulata and Zea mays field.(2) The activity of soil catalase, urease, protease and phosphatase was significantly different in different soil layers in each land use pattern respectively, except for the invertase activity. In the soil layer of0～20cm and20～40cm, the activity of soil enzymes was significantly different among different farmland uses, while the activity of protease did not show significant difference among all the farmland use patterns.(3) The quantity of bacterial, fungi and actinomycetes decreased significantly with soil depth, and was also significantly different among all the farmland use types in the same soil layer.(4) The quantities of soil microorganisms, activities of five major soil enzymes and soil chemical properties interacted closely.