Experiment And Simulation Study On Phosphorus Migration And Transformation In Soil Under Variable Waterlogging

Phosphorus is an indispensable element for the growth and development of plants.In order to increase agricultural production,a amount of phosphate fertilizer is embarked into farmland.Only some of the phosphate fertilizer applied to can be absorbed and utilized by crops in the farmland,which led to a large accumulation of phosphorus in the farmland.And phosphorus was enriched in soil.In the flood basin,along with surface runoff and even migrate vertically in the soil,phosphorus in the soil was carried into the water that flowed into rivers and lakes in the process of flood submergence and flood vanish,which could increase the risk of eutrophication of lakes and rivers.When the flood submerges the soil,being soluble active phosphorus?SRP?,phosphorus is desorpted from the soil and dissolved in water.After the flood recedes,soluble active phosphorus was carried into the rivers and lakes,which cause eutrophication of the water.Therefore,according to the law of varying waterlogging,it is very important to study the mechanism of phosphorus transfer and transformation under variable waterlogging.The research results can provide scientific method for the eutrophication of water caused by agricultural non-point source pollution.Taking alkaline farmland soil as the research object,the thesis adopted the indoor soil column model experiment and combined the theoretical knowledge of soil phosphorus adsorption to desorption the migration and conversion of phosphorus in the soil profile under the submerged-discharge-submerge-discharge-flooding condition.A one-dimensional flow model and a solute transport model was established to further analyze the rules of the migration and adsorption of SRP in soil profiles.With experimental research and simulation prediction in paper,three conclusions can be drawed in the following:?1?Analysis of the variation law for phosphorus in overlying water and draining water of different depths by flooded drainage.The results show that the Langmuir isotherm model is best for soil phosphorus adsorption,and the maximum phosphorus adsorption capacity is 335.57mg·kg^-1 soil for experimental soil samples.The results of SRP migration experiments in indoor soil columns are summarized.The distribution of SRP concentration in the soil profile of the soil column was different,and the SRP concentration varied from 0.2 to 2.5 mg·L^-1.During the first flooding period,the SRP concentration in the overlying water ranged from 3 to 35 mg·L^-1,while the SRP concentration at the observation point ranged from 0.2 to 2.5 mg·L^-1.Overlying water was observed as the number of flooding days increased.When the concentration of SRP decreased,the concentration of SRP at the observation point increased,and the highest concentration of SRP in the soil profile appeared at a depth of 5 cm observation point position.The highest concentration of SRP at the 19th day of flooding was 2.5 mg·L^-1.As the depth increases,the highest concentration of SRP decreases continuously.With the increase of the number of flooding,the SRP concentration of overlying water decreased from 34.5 mg·L^-1 to 0.3 mg·L^-1,and the concentration of SRP at the depth of 5 cm decreased from 2.5 mg·L^-1 to 0.08 mg·L^-1.Other observations decreased from 0.7 mg·L^-1 to 0.08 mg·L^-1.?2?.Analysis on the transformation of soil total phosphorus and various forms of inorganic phosphorus by flooded drainage.Studies have shown that after the first flood,the total phosphorus?TP?content in the soil profile increased by 5%to 10%before flooding,and after the second flood,the total phosphorus content in the soil profile was 5%to 15%lower than before.After the first flood,the soil profiles of Ca₂P,Ca₈P,Fe-P,and O-P were reduced by 15%to 40%,40%to 90%,20%to 60%,and 80%to 95%,respectively,before flooding.The soil profile of Al-P and Ca₁₀P increased by 10%to 20%and 20%to 50%before flooding,and after the second flood,the soil profile of Ca₁₀P decreased slightly,which was about5%lower than that before the second flooding.Other forms of inorganic phosphorus increased different,and the mean increase in Fe-P reached 20 mg·kg^-1soil in the soil profile,which was 30%to 80%higher than before.Soil profiles Ca₂P,Ca₈P,Al-P and O-P are stable.?3?One-dimensional flow motion and solute transport model based on soil column model measurement data was constructed,and the model by measuring SRP concentration results at the observation point was identified to demonstrate the rationality of the model.The isothermal adsorption parameters and the molecular diffusion coefficient of the model were calculated to be 60cm²·d^-1.The model prediction results showed that the changes of the initial SRP concentration and the change of the depth of flooding all affected the migration and adsorption of SRP in the soil profile,With the flooding time prolonging,the concentration of SRP increased in the soil profile,while the concentration of SRP in the Overlying water observation continued to decrease.