Initial Study On The Coupling Correlations Between Organic Carbon And Inorganic Carbon On The Loess Plateau

To evaluate the coupling relation between soil organic carbon and inorganic carbon in soil, collecting profile data of the second national soil survey of the Loess Plateau was to deliberate organic carbon storage and density, effects of land uses, elevation, average annual rainfall and temperature, and analyzed the correlations between the contents of organic carbon and inorganic carbon surface soil under different average annual rainfall in this study. On the other hand, regarding four topographies (tableland, terrace, slopeland and gullyland) and five land uses (shrubland, woodland, grassland, tillage and orchard) of Zhi Fanggou watershed in hilly and gully region as the object of study was to analyze the distribution of organic carbon content soil surface and profile under different topography and land uses. The main results as follows:On the Loess Plateau0-20cm and0-100cm soil organic carbon storage were1.68Pg and5.32Pg, respectively, the average density of organic carbon were2.69kg/m2and8.99kg/m2, the reserves of the organic carbon reserves in China respectively were1.90%and6.00%. The distribution area of soil types played a critical role in organic carbon content, and soil organic carbon on the Loess Plateau mainly distributed in ash brown soil and yellow loamy soil which have large area, the content of organic carbon were very low in alkaline grey desert soil and swamp soil which have small area. Compared with the eastern and southern of China, the density of soil organic carbon on the Loess Plateau is lower. Land uses and climate factors such as average annual temperature and rainfall and elevation had significant effects on the distribution of soil organic carbon content.Topography and land uses significantly (P<0.05) influenced soil profile organic carbon content in hilly-gully region on the Loess Plateau. The order of soil organic carbon contents influenced by topography factors were gullyland>lower slope>middle slope>upper slope>terrace>tableland. The order of soil organic carbon contents influenced by land uses were shrubland>grassland>woodland>tillage>orchard. The interaction between topography and land uses very significantly (P<0.01) influenced soil profile organic carbon content in hilly-gully region on the Loess Plateau. Soil organic carbon storage in deep soil in Zhifanggou watershed was large. The organic carbon reserve in20-100cm soil accounted for67.70%of that in0-100cm soil, the organic carbon reserve in100-200cm soil accounted for40.70%of that in0-200cm soil.On the Loess Plateau there were close relationships between soil organic carbon and inorganic carbon. Under500-800mm average annual rainfall there was significant negative correlation between organic carbon and inorganic carbon in surface soil, and under300-400mm there was not significant positive correlation between the two, but under<300mm there was significant positive correlation between the two.Topography (slope situation, slope direction and slpoe length) influenced the redistribution of land uses and soil moisture through the effects on illumination, temperature and rainfall, so could indirectly influenced the distribution of soil organic and inorganic carbon in hilly-gully region on the Loess Plateau. For topography, there were significant negative correlations between soil organic carbon and inorganic carbon in0-20cm and20-60cm layer under slopeland. There was significant negative correlation between soil organic carbon and inorganic carbon in0-20cm layer under tableland. There was no correlation between soil organic carbon and inorganic carbon under gullyland. For land uses, there were significant negative correlations between soil organic carbon and inorganic carbon in0-20cm and20-60cm layer under grassland, shrubland and woodland. There was significant negative correlation between soil organic carbon and inorganic carbon in0-20cm layer under farmland.