Friday, 14 July 2006

Spatial Variation of Chemical Properties as Affected by Soil Erosion on Hillslopes and Terraces of Hilly Areas of Sichuan, China.

Shijun Ni1, Jianhui Zhang2, Xianghao Zhong3, and Shuzhen Liu3. (1) Chengdu University of Technology, 1 East Road 3, Erxian Bridge, Chengdu 610041, China, (2) Institute of Mountain Hazards & Environment, Chinese Academy of Sciences, PO Box 417, Chengdu 610041, China, (3) Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, PO Box 417, Chengdu 610041, China

The variation in soil nutrients that is crucial to the productivity of soils undergoing erosion and overall results in a decline in soil quality and crop production in the whole landscape. Two toposequences (the long slope and terraced field series) were selected from hilly areas of the Sichuan Basin, China to determine effects of soil redistribution rates and topographic changes on nutrient and chemical element dynamics, and examine the contribution of water erosion and tillage erosion to the variation and distribution pattern in soil nutrients and chemical properties within different landscapes. For the long slope, soil loss occurred at upper slope positions and a relative soil accumulation was present at lower slope positions. However, terrace bank create the line of zero downslope transport of soil, leading to abrupt changes in 137Cs inventories over very small spatial range between the upper (or lower) part of the terrace and the lower (or upper) part of the immediate terrace. Significant correlations between total P, K and 137Cs concentrations suggest that the distribution of total P and K is related closely to soil redistribution. Extractable K concentrations (g m-2) are also highly related to 137Cs on both the long slope and terraced fields. However, it is notable that no close relationship between extractable P concentrations (both mg kg-1 and g m-2) and 137Cs was found on the terraced fields, while there was a significant correlation between the two variables on the long slope. The variation in extractable P by soil redistribution was enhanced on the long slope, but was concealed on the terraced fields due to CaCO3. It is suggested that the variation in extractable P not only depends on soil redistribution in relation to fine soil particles, but also is influenced by other factors such as the P-fixation due to CaCO3 derived from parent materials which itself is linked to soil erosion and redistribution, and therefore extractable P dynamics in reference to soil erosion is relatively complex on carbonate-rich soil and parent materials in such areas as the Sichuan Basin. Tillage erosion, the dominant soil redistribution process on terraced fields was found to be a major contributor to the spatial variation in soil chemical properties in the terraced field landscape, while water erosion plays an important role in the variation in soil chemical properties in the long slope landscape. In the case of carbonate-rich soils or parent materials, however, tillage erosion would not create accumulations of extractable P in depressions, whereas water erosion results in extractable P losses at upper slope positions and accumulations at lower slope positions.

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