Forming Process of Diagnostic Horizon of Loutu Soil and Its Significance in Guanzhong Areas

【Objective】Through extensive analomical analysis of Loutu soil profile in Guanzhong Areas, this paper tries to illustrate the forming process of diagnostic horizon and its significance.【Method】According to data from field investigations and experimentations in laboratory, the Loutu soil profile was anatomized at diagnostic horizon dividing, micromorphological features soil profile pattern difference and soil age.【Result】Bt horizon was formed from 8 500 to 3 100 a B.P., Bc horizon from 3 100 to 2 000 a B.P., and Ap horizon has formed since 2 000 a B.P. Bc horizon very resemble the Malan Loess in physical and chemical characters, structure and micromorphological features, but it has distinct difference with Ap horizon and Bt horizon. Comparability coefficient, between different horizons and Malan loess, is 0.8105-0.8951 in Ap horizon, 0.9051-0.9352 in Bc horizon and, 0.6718 in Bt horizon, respectively. 【Conclusion】All the results in this study suggest that Loutu soils have Ap1-Ap2-Bc-Bt-Bk-C profile pattern, which is caused by change of the soil forming intensity that is caused by environmental change. Ap horizon has formed since 2000 years, which infliction loessal dung and eolian dust deposition and cultivation occur simultaneously in the process of Ap horizon-formation, which is mainly controlled by the degree and manner of human activities. Bc horizon is aeolian sedimentary deposit in relative aridity period during 3 100-2 000 a B.P., with weak degree of soil forming. Bt horizon is formed during the Holocene Megathermal.