Simulated Effects Of Organic Acids In Rhizosphere Environment On Phosphorus Release In Wetland Soils

The phosphorus deficiency in soil is becoming more and more serious.A large amount of phosphorus fertilizer added to ensure the agricultural productions.The low absorption rate of phosphorus in crops may cause phosphorus loss and local non-point source pollution.From the perspective of ensuring the green and sustainable development of agricultural production and ecological environment protection,the research on the activation of soil phosphorus by low molecular weight organic acids is important particularly.The key point is that the selection of species and concentration of low molecular weight organic acids can provide technical support for the application of organic acids in regulating soil phosphorus in a large scale.Many studies focus on the ecological effects of organic acids,however,the results and conclusions are influenced by many factors such as soil properties,types and concentrations of organic acids,and other factors.In this paper,wetland soil and farmland soil samples were collected,citric acid,oxalic acid,tartaric acid and malic acid were selected as low molecular organic acid extracted soil phosphorus by chemical extraction method,and soil phosphorus concentrations were measured by phosphorus molybdenum blue colorimetric method.The phosphorus release characteristics of four low molecular weight organic acids in soil under different conditions were studied,and the effects of organic acid concentration,organic acid type and soil type on phosphorus release were discussed.The results were as follows:(1)Four organic acids were detected in three different lakeside soils and three different paddy soils.Organic acid contents were ranged from 0.76 to1.79 mg/Kg.The content of citric acid was higher,followed by oxalic acid and malic acid,and tartaric acid was the lowest.(2)Organic acids could activate phosphorus in lakeside wetland soil and farmland soil in a certain concentration range.Due to the difference of organic acid type,additive concentration and soil type,its activation ability to soil phosphorus is different.In all tested soils,the adsorption rates of phosphorus extracted by citric acid and oxalic acid increased and then decreased in the range of 0～20 mmol/L concentration,while the adsorption rate of phosphorus extracted by tartaric acid and malic acid increased with the increase of organic acid concentration.(3)Under the treatment of citric acid and oxalic acid,the maximum phosphorus release of wetland soil in winter was in the concentration range of 2～8mmol/L,and the maximum phosphorus release of wetland soil in summer was in the concentration range of 5～10mmol/L.In winter,Caizi Lake and Wuchang Lake had the strongest phosphorus release capacity under citric acid treatment,and Pogang Lake had the strongest phosphorus release capacity under malic acid treatment.In summer,the phosphorus release capacites of Caizi Lake and Pogang Lake were the strongest under oxalic acid treatment,and the lowest under tartaric acid treatment,while Wuchang Lake was the strongest under tartaric acid treatment.(4)The maximum amount of phosphorus released by citric acid,oxalic acid,tartaric acid and malic acid appeared in the concentration range of 5～10 mmol/L in farmland soils.Among the three sampling sites tested,the farmland soils of Xilian had the highest phosphorus release capacity under the treatment of tartaric acid,and the lowest phosphorus release capacity under the treatment of citric acid.The farmland soils of Zhongcang and Shifeng had the highest phosphorus release capacity under the treatment of citric acid.In summary,phosphorus release of soil was influenced by the concentration,type of low molecular weight organic acids,and soil properties.The four low molecular weight organic acids can promoted the release of soil phosphorus in low concentration,while showed the regularity of inconsistent in high concentration.The results showed that different response mechanism of organic acids on soil phosphorus release,which can provide scientific basis for selecting low molecular weight organic acids to activate soil phosphorus.