The Differences Research Of Dissolved Organic Carbon Sorption In Upland Soil And Paddy Soil

In order to reveal the process and mechanism of dissolved organic carbon(DOC)adsorption and desorption in soil,the typical upland soil and paddy soil and its typical soil minerals(kaolinite,montmorillonite and goethite)in red soil area of tropical area were studied in this paper.The process of DOC isotherm adsorption and desorption in soil and its typical minerals was quantitatively studied by controlling the conditions of the amount of DOC added,pH and DOC composition using the batch adsorption equilibrium method.The change characteristics of the aromatic components of DOC,the amount of DOC adsorption and desorption after adsorption equilibrium were analyzed.Also the difference mechanism of DOC adsorption and desorption in two soils was systematically discussed in this paper.This study can preliminary reveale the relationship between the process of DOC adsorption and desorption and pH or DOC composition in paddy soil and upland soil,and provide the theoretical basis for the regulation of soil organic carbon(SOC)in farmland soil.The main conclusions were as follows:(1)The proportion of aromatic components of paddy DOC(DOC from the paddy soil condition)was significantly reduced after adsorption in soil,and the adsorption amount of aromatic components decreased with increasing pH.The proportion of aromatic components of upland DOC(DOC from the upland soil condition)was no significant change after adsorption in two kinds of soils.The change of proportion of aromatic components of upland DOC which adsorbed by kaolinite and mixed minerals were not significant,but the proportion of aromatic components of upland DOC which adsorbed by montmorillonite and goethite were significantly increased.The proportion of aromatic components of paddy DOC which adsorbed by soil minerals were significantly decreased,and the adsorption capacity was kaolinite<mixed mineral<goatite<montmorillonite.(2)With the increase of the initial concentration of DOC,the capacity of DOC adsorption in upland soil and paddy soil and its typical minerals increased.The effect of soil use on the process of DOC adsorption was less,which was not the main reason for the difference of the capacity of DOC adsorption in upland soil and paddy soil in the field conditions.The farmland soils were most acidic in the red soil area,and the capacity of DOC adsorption in montmorillonite was higher than other minerals and,followed by goethite and mixed minerals,finally by kaolinite.The amount of DOC adsorption in mixed minerals was the closest to goethite.Under the condition of pH4,the amount of paddy DOC desorption in paddy field was significantly higher than that in upland soil,but the soil type had no significant effect on the capacity of DOC desorption in soil in other reaction conditions,DOC desorption behavior is not only related to the specific surface area of minerals,but also significant impacted by the pH and DOC composition.The stronger the capacity of DOC adsorption in the minerals,the weaker the capacity of DOC desorption.The results showed that the adsorption and desorption of DOC in soil solution were affected by soil mineral species.(3)Under acidic conditions,the capacity of DOC adsorption in soil and its typical minerals decreased with the increase of pH.The upland soil and paddy soils in red area were acidic.The DOC composition was not the main reason for the difference of the capacity of DOC adsorption in upland soil and paddy soil under field conditions,but pH was the main influencing factor.The capacity of paddy DOC adsorption was significantly higher than upland DOC in the alkaline soil,and the composition of DOC had a significant effect on soil DOC adsorption.Acidic conditions was favorable for the desorption of DOC in paddy soil,but it was not conducive to the desorption of DOC in upland soil.The rate of paddy DOC desorption in kaolinite was pH6>pH4>pH8.The rate of paddy DOC desorption in montmorillonite,goethite and mixed minerals decreased with the increase of pH.The rate of upland DOC desorption in typical minerals increased with increasing pH.In summary,it was shown that the difference of DOC content in upland soil and paddy soil was influenced by pH and DOC.(4)The IM isotherm equation,Freundlich equation,Langmuir equation and Temkin equation were used to fit the capacity of DOC adsorption.And invented that coefficient of determination of the isothermal adsorption fitting equation was influenced by mineral type,environmental pH and DOC composition.