Characteristics Of Phosphorus Pool In Farmland Soil And Activation Of Phosphorus By Different Acids In Guanzhong Plain

In China,fertilization habits are greatly influenced by national policy guidance and human factors,resulting in the surplus and accumulation of phosphorus in farmland.At the same time,with the adjustment of fertilization habits,the balance of phosphorus in soil has been changing.Therefore,it is an important link for agricultural sustainable development to understand the existing phosphorus status in soil and make full use of the phosphorus remaining in soil.Aiming at the problem of unscientific fertilization in Guanzhong area,this paper investigated the characteristics of phosphorus in Farmland soil in this area,and made clear the contents of total phosphorus,available phosphorus and the characteristics of inorganic and organic phosphorus components in the area.By adding different concentrations of oxalic acid,citric acid,hydrochloric acid and sulfuric acid to the soil,the dynamic changes of soil p H,water-soluble phosphorus and available phosphorus and the transformation between different forms of inorganic and organic phosphorus were analyzed,and the activation effect of different acidic substances on phosphorus was clarified.Finally,oxalic acid and sulfuric acid,which had better phosphorus activation effect in the culture experiment,were selected for pot experiment,and were applied to the soil once before sowing.After harvesting,the dry weight of wheat and its absorption of nitrogen,phosphorus and potassium nutrients were analyzed,so as to explore the activation effect of different acidic substances on soil phosphorus and their effects on crop growth and development.The main conclusions are as follows:（1）The contents of total phosphorus and available phosphorus in Farmland soil in Guanzhong Plain generally showed a decreasing trend from west to east.The total phosphorus content ranges from 0.52 to 1.32 g kg^-1,with an average content of 0.89 g kg^-1,and the available phosphorus content ranges from 12.40 to 77.83 mg kg^-1,with an average content of 32.11 mg kg^-1,which is quite different among different regions.Inorganic phosphorus is the main component in the study area,accounting for 78.12%of the total phosphorus content,and calcium and phosphorus are the main components in inorganic phosphorus.Organic phosphorus is mainly moderately active organic phosphorus.The contents of different phosphorus components in the soil in the study area are as follows:Ca₁₀-P>Ca₈-P>ML-OP>Al-P>Fe-P>O-P>HR-OP>Ca₂-P>MR-OP>L-OP.（2）Oxalic acid,citric acid,hydrochloric acid and sulfuric acid can activate potential phosphorus sources in soil by changing soil p H,and the activation effect is closely related to the type and concentration of acid.The ability of two inorganic acids to reduce soil p H is greater than that of organic acids,and the p H of H3 and S3 treatments decreased by 1.01and 0.72 units respectively compared with CK.The ability of inorganic acids to activate available phosphorus is significantly greater than that of organic acids,and the average increment of available phosphorus in H3 and S3 treatments is 56.91 mg kg^-1and 129.59 mg kg^-1,respectively.Adding 9.8 ml of oxalic acid with the concentration of 40 mmol L^-1increased the content of Ca₂-P in soil by 22.08 mg kg^-1,and decreased the content of Ca₁₀-P and HR-OP by 47.68 mg kg^-1and 16.79 mg kg^-1,respectively.Adding 9.8 ml of sulfuric acid with the concentration of 40 mmol L^-1increased the content of soil Ca₂-P by 124.25mg kg^-1,and decreased Ca₈-P and Ca₁₀-P by 41.17 mg kg^-1and 102.22 mg kg^-1,respectively.Organic acids mainly promote the decomposition of insoluble organophosphorus,while inorganic acids mainly promote it.（3）Applying 200 ml oxalic acid with a concentration of 60 mmol L^-1once before sowing significantly promoted the increase of wheat dry weight by 13.13%in Qishan（QS）soil,but had no significant effect on the absorption of nitrogen and phosphorus by wheat.Applying 200 ml sulfuric acid with concentration of 40 mmol L^-1once before sowing reduced the dry weight of wheat by 5%in Qishan（QS）soil,but significantly promoted the absorption of phosphorus by wheat,with the maximum increase of 36.19%.When sulfuric acid is used to improve soil and crop growth,it should be adapted to local conditions,especially for poorly ventilated soil.To sum up,the level of phosphorus in farmland soil in Guanzhong plain is high,and a large amount of phosphorus has accumulated in the soil;Adding different acids can achieve the purpose of activating phosphorus,and its activation is mainly realized by transforming insoluble phosphorus components into highly effective phosphorus components;The effects of oxalic acid and sulfuric acid on wheat seedling growth show different effects due to different soil properties,and their effects on soil phosphorus components are consistent with their effects on wheat phosphorus absorption.