Preliminary Analysis on Abnormal Granularity Layers of Soil Profile and the Response of Relative Factors in Loess Plateau

[Objective] The paper was to analyze organic carbon content (SOC), granularity, total nitrogen content (TN), carbon-nitrogen ratio (C/N), calcium carbonate content (CaCO3) of 1cm soil profiles in returning forest in Zhifanggou watershed of Ansai County in Loess Plateau, so as to study the changes of physical and chemical properties in abnormal layer of soil reflected with granularity, as well as the physical and chemical responses of soil. [Method] Three quadrats with the size of 10 m×10 m were randomly selected in three sampling plots in Loess Plateau, three profiles in upper, middle and lower slope were excavated, and the samples were collected with interval of 10 cm; the surface layer with the depth of 0-10 cm was divided into two layers of 0-5 and 5-10 cm for sampling, respectively. Eleven samples were collected in each profile with a total of 99 samples. Its organic carbon content, granularity, total nitrogen content, carbon-nitrogen ratio and CaCO3 content were analyzed. [Result] The soil profiles in three sampling sites contained five characteristic layers, including a1, b1, b2, c1 and c2, the content of soil granule with particle size less than 0.02 mm decreased, and those with particle size 0.02 mm increased, the organic carbon content and C/N value (a1, b1, b2, c2) increased, but the increase trend of CaCO3 content was not obvious. [Conclusion] The study shows that the characteristic soil layer is commonly existed in loess region, especially the eroded loess region, which should be paid attention in the research fields of modern soil science and ecology.