The Influence And Spatial Variability Of Main Clay Mineral Composition In Loess On The Soil Fertility And Corrosion Resistance

Since the quaternary period, loess plateau is the deep loess sediments formed and developmentaled with special landform types, it is the world’s lagest loess deposition area,so it is an ideal area of study the soil erosion and nutrient change. Based on the loess plateau, this paper selected eight typical small watersheds as the research object. The latitude of research area range from34°45’to39°45’, each basin choosed9sampling points in the relative consistent patterns of land use from slope top to bottom (Liudaogou had7sampling points), each sampling point took0-20cm and20-40cm two layers,for a total of140soil samples.Through determining the content of organic matter, the total nitrogen, the available phosphorus, the exchange capacity of cation, the moisture content in air dried, the composition of soil mechanical, the content of water stable aggregate, the damage rate of structure and the main minerals in the clay soil, this paper discussed the influence mechanism and spatial variability of mineral composition on the soil corrosion resistance and fertility, and the main research results were as followed:1. The content of all fertility index in the plough layer were higher than the b-horizon layer (except a few sampling points), it showed that the nutrient supply ability of plough layer was stronger than the lower. From slope top to bottom, the organic matter, total nitrogen and available phosphorus showed an increasing trend, accompanied with the soil erosion, the soil nutrient deposited down in the mid-lower of each basin; add the interaction between the nutrients, the change of the nutrient content were consistent with the slope change. The exchange capacity of cation presented an increasing trend only in basin of Wufendigou, Nihegou and Zhifanggou from slope top to bottom, and showed a reverse trend in other basins.2. With the reduce of latitude, the soil nutrient displayed an increasing treand from north to south in study area. The total nitrogen, available phosphorus and the exchage capacity of cation were all achieved a maximum in Nihegou which is the lowest latitude basin, the organic matter achieved maximum in Liudaogou. In all, the soil nutrient condition showed a certain latitudinal zonality.3. In the study area, soil organic matter content with illite and chlorite content was a significant positive correlation, but with the orthoclase showed significant negative correlation. The total nitrogen conent with illite content was a highly significant positive correlation. The effective phosphorus content with orthoclase content showed significant negative correlation. The cation exchange capacity with chlorite content was a significant positive correlation, but with orthoclase and anorthite had significant negative correlation.4.It leaned to sandy soil in study region. Because the sand content account for more than60%, so in the same basin, the impacts of external environments on the sand content were not great, but to silt and clay content would have a considerable impact. Besides the Liudaogou basin, the water stability aggregate content of other basins reduced from slop top to bottom, and the soil structure body damage rate showed the opposite trend. It demonstrated that with the decreasing of sampling points height, the soil water erosion resistance ability strengthened in the same basin, and the soil erosion phenomenon would be lightening.5. The soil corrosion resistance showed a certain regularity by the double effect of latitude and landform types in study area. With Jiuyuangou as the center, the water stability aggregate content on both sides have an incredsed trend, meanwhile the strcture body damage rate showed the opposite changes. With lower latitude, soil sand presented decreasing trend, the silt and clay content presented the increasing trend, this showed that with lower latitude, soil texture tend to be good.6. From north to south, the change trend of illite and clay almost unanimously. The change trend of chlorite and kaolinite content with clay content was consistent in the first four basin, in the last four river basin, it showed opposite changes. The change trend of orthoclase content and water stability aggregate content was almost the contrary. In Jiuyuangou, soil water stability aggregate content achieve minimum value, and the orthoclase content was the highest.7. The main mineral showed latitude zonality in study area. And the clay minerals were mainly consists of illite. With latitude reduced, three kinds of clay mineral which included illite, kao linite and chlorite showed an increasing trend. The study area primary mineral was calcite, feldspar secondly. Calcite and feldspar content were all decreased with latitude reduction. It stated that the dry climate transform to hot and humid climate with latitude reduced, suitable climatic conditions conducive to mineral weathering.