Different Tillage Influence On Topsoil Structure And Organic Carbon In Cropland

Soil erosion is severe in west Loess Plateau, and the topsoil erosion is a main reason for degradation of cropland in this region. So far, many works have been done to try to stop the trend and protect soil, but soil degradation problem is still there or become more and more serious of whole region, caused by the complexity and difficulty of that problem. High rainfall variety and poor management of soil and water are the most important and limiting factors in crop system in this region. In agricultural management, tillage systems affect soil productivity through influences on soil properties. In Huangmian soil of Loess Plateau, however, there are not clearly understand for the aggregation characteristic, structure stability and infiltration characteristic under long term tillage. Through 2 experiments in Dingxi, China, and 3 experiments in New South Wales, Australia, the research was focused on aggregation characteristic of Huangmian soil and the effects of rotation and tillage types on topsoil structure properties and organic carbon accumulation. The results are summed up as below:A. Effects of long term tillage and cropping on topsoil structure stability and organic carbon accumulation of Huangmian soila. Generally, topsoil structure stability of Huangmian soil is very low and easily slaked in water. The water stability macroaggregates contents of long term tillage and 30 yrs lucerne fields were only 7% and 22% separately. Both in 0-5 cm and 5-10 cm layer, the water stability macroaggregates content of long-term tillage field was significantly low than that of 30 yrs lucerne field. Macro-aggregates of Huangmian soil are not only made up of micro-aggregates, but also silt and clay. This is different with the hypotheses of soil structure hierarchy. It is showed that the traditional microaggregates-macroaggregates model could not suit to Huangmain soil completely. This result can as a supplementary of the model for poor structure soil.b. Soil organic carbon content of long-term tillage field was significantly low than that of 30 yrs lucerne field. Both total organic carbon (TOC) content and percentage of easy oxidizible organic carbon fraction on TOC were increased in topsoil of 30 yrs lucerne field. The organic carbon content and the percentage of easy oxidizible organic carbon fraction on TOC were decreased with depth in topsoil of Huangmian. The larger the water stable macroaggregates, the higher organic carbon content in them. Soil management has significant impact on organic carbon in macroaggregates, but not on that in microaggregates.c. In topsoil of Huangmian, soil total organic carbon and easy oxidizible organic carbon fraction has significantly positive correlation with structure stability indexes, but difficult oxidizible organic carbon fraction has no significant correlation with these indexes.