Study On The Acid Base Buffer Capacity Of Variable Charge Soils By Potential Titration

Compared with the constant charge soils that distribute in temperate regions,the variable charge soils in South China are unique,with highly variable particle surface charges.The soils distributed in South China are typical variable charge soils.which rich in iron and aluminum oxides and colloid surface charges are variable.South China is the main agricultural production base in China,which rich in crops（such as rice,etc.）,cash crops（such as tea,vegetables,etc.）,fruits（such as bananas,citrus,etc.）,oil crops（such as peanuts,etc.）.However,the variable charge soils are seriously acidified in South China,which not only pollute the environment but also restrict the sustainable development of agriculture.Therefore,it is of great significance to strengthen the study on the acid base buffer mechanism of the variable charge soils in South China for the construction of ecological environment and the sustainable development of agriculture.In this thesis,In order to explore the natural environmental characteristic factor and long-term application of organic fertilizer on the influence of variable charge soil acid base buffer capacity,we chose the variable soils of Yingtan City,Guangxi Province as the research object,using potentiometric titration,and combined with the surface complexation model（SCM）,X-ray diffraction（XRD）,high-resolution transmission electron microscopy（HRTEM）and energy spectrum（EDS）,and other means.At the same time analyzed the effect of artificial fertilization disturbance on the acid base buffer system of variable charge soils and its mechanism from the microscopic level of element enrichment and mineral transformation.And the main conclusions are as follows.（i）This thesis established a set of suitable for variable charge soils acid base buffer capacity of the new method of trace and fast potentiometric titration,namely under the condition of the guarantee consistent electrode health,with 1.2 L/h in the suspension velocity of ventilation with N₂,respectively by 0.01,0.1,0.3 M Na Cl solution as electrolyte solution,balance 0.5 h before titration,with 6μL/20 s titration speed,the system of titration to p H 3,again to return to the titration to p H 9.And we to verify the feasibility of this method by surface complex model.（ii）It was also found that the concentration of surface species（≡SOH,≡SOH₂⁺and≡SO^-）would change by the S/L ratio in the range of 2 g/L to 16 g/L,thus further affecting the surface charge properties of the variable charge soils.In the range of 288 K to 303 K,the increase of temperature not only increases the number of species concentration on the surface,but also leads to the expansion of protonation/deprotonation range,which may further increase the acid base buffer capacity of the soils.（iii）It was also revealed that the application of organic fertilizer not only improved soil acidification,but also made the formation of clay mineral-iron oxide complex between iron oxide and clay minerals to provide a large number of sites for nutrient elements,thus promoting the conversion of 2:1 type layered silicate minerals to 1:1 type clay minerals,so as to improve soil acid base buffering capacity.