Quantifying Agricultural Land Degradation Processes Related to Soil Carbon and Nitrogen Redistribution in Western China Using Fallout Radionuclide (FRN) and 6~(13)Cs Techniques

摘要

Over the last 50 years, soil erosion rates at field scale have been well documented in China, but knowledge of their quantitative impacts on soil quality is very limited, especially on an area-wide basis. The objective of this study was to quantify the agricultural land degradation processes related to soil carbon (C) and nitrogen (N) redistribution in cultivated slope land of the Chinese Loess Plateau. A cultivated sloping land (a slope gradient of 3.1°-16.8°) in Pucheng County on the Loess Plateau was selected and the history of upland degradation processes reflected by changes in water and tillage erosion and crop productivity was reconstructed through the dated chronology of soil accumulation at deposited sites using fallout radionu-dides(FRNs) caesium-137 and excess lead-210 (~(137)Cs and 210Pbex), and sources of soil organic carbon (SOC) were identified using 6~(13)Cs tracer. The results showed that between 1954 and 2008, bulk soil translocation processes arising from intensive tillage activities were mainly responsible for land degradation in the cultivated slope catchment. Further, changes in crop productivity could be determined from records of C input by crop roots derived from the deposited profile. Models were established using FRN integrated with terrain attributes for slope-catchment evaluation of SOC and total nitrogen (TN) stocks covering a timeframe of 50-100 years. These models had a very high accuracy for quantifying changes in SOC and TN stocks in cultivated slope catchments. Using FRN profile dating in combination with natural 6,3C tracer, it was possible to explain the role of water erosion and intensive tillage processes in affecting upland degradation over the past 100 years.