High-resolution studies of the oldest cultivated soils in the southern Loess Plateau of China

The Holocene loess-soil sequence on the Chinese Loess Plateau constitutes an excellent record of evolution of soil formation, monsoonal climate, eolian dust accumulation and influences of arable farming of over 8000 years. A high-resolution soil profile on the Zhouyuan loess tableland to the west of Xi'an was studied using particle-size analysis, measurement of magnetic susceptibility, total Fe, TOC and CaCO3. The results provide new insights into the roles of eolian dust deposition and human impact of cultivation on soil development in this environmentally sensitive zone. Several loess layers are found interbedded with cinnamon soils in the profile. This has been caused by changes in rainfall and intensity of dust deposition that is forced by changes in balance between the northwest continental monsoon and southeast maritime monsoon of East Asia during the Holocene. The processes of soil formation were interrupted several times by intensified dust-fall and climatic aridity in the last 11,500 years. The initial clearance of forest for arable farming occurred at ca. 7500 years BP on the loess tableland. It was contemporaneous with the arrival of the wetter and warmer climate of the Holocene Megathermal (8500-3100 years BP). Thereafter, arable fanning has been maintained during both the time of soil formation and that of intensified dust accumulation, though there could be temporary cessation or reduced intensity of cultivation in the drier intervals because of lack of rainfall and soil moisture. Increased intensity of dust accumulation has been ongoing since ca. 3 100 years BP in the Loess Plateau. A loess deposit of 40-80 cm has overlaid the Multiple or single-welded cinnamon soils on the flat land over the plateau. (C) 2002 Elsevier Science B.V. All rights reserved.