Effects Of Different Phosphate Fertilizer Application Rates On Soil Phosphorus Fractions And Bioavailability Under Long-term Experiment

The long-term application of phosphate fertilizer in agricultural production can cause P accumulation in soil,which not only affects the utilization rate of phosphate fertilizer,but also causes the risk of resource waste and phosphorus loss.Based on the long-term positioning test of calcareous fluvo-aquic soil to study the accumulation and consumption of phosphorus.The classification of inorganic phosphorus in soil was determined,and the relationship between available phosphorus and various forms of inorganic phosphorus determined by Olsen-P method,Mehlich3 method,resin exchange method and CaCl₂ method was discussed.The soil solution was extracted by laboratory culture test.By analyzing the ion composition,ion activity and Phosphate forms in different P treatments,the existence mechanism of soil Phosphate in fluvo-aquic soil was theoretically confirmed,and the control system and influence factors of phosphate solubility and availability in calcareous soil could be found out.The pot experiment of wheat was conducted to study the transformation of phosphorus in soil and the factors affecting bioavailability.The main results were summarized as follows:?1?Analysis and evaluation of soil P status under different phosphorus application levels in a 7-year long-term fertilization experiment of wheat-maize rotation.Compared with the initial soil,the total phosphorus of CK and P0 treatments were decreased by 15.2%and 29.7%,respectively,with the total amount of inorganic phosphorus decreased by 13.5%and 11.8%;the total amount of total phosphorus treated by P2 and P3 were increased by 8.2%and 27.2%respectively,with the total amount of inorganic phosphorus increased by 11.1%and 27.8%.The content of inorganic phosphorus in the tested soil was mainly Ca₁₀-P and Ca₈-P.The application of phosphorus fertilizer could increase the relative proportions of Ca₂-P,Ca₈-P,Al-P and Fe-P.In the depletion state of phosphorus,the inorganic phosphorus used by plants mainly came from slow-release phosphorus sources?Ca₈-P,Al-P,Fe-P;75%?,un-available phosphorus sources Ca₁₀-P?11.5%¹4.0%?,and available phosphorus sources Ca₂-P?7.5%⁸.9%?;At inorganic phosphorus surplus condition,excess inorganic phosphorus mainly converted to Ca₈-P?50%⁷0%?,Al/Fe-P?10%²3%?,O-P?8%?,and Ca₂-P?0.2%¹.8%?.Path analysis and stepwise regression analysis results showed that:Ca₂-P,Al-P had positive effects on available phosphorus extracted by four methods with the greater contributions.Ca₂-P and Ca₈-P could be effectively extracted by the Olsen method.WHile,the Mehlich3 method mainly extracted Ca₂-P,Ca₈-P and Al-P,the main extraction of AEM were soil Ca₂-P and Fe-P,and CaCl₂ method mainly extracted Ca₂-P.All the four methods were feasible for determining soil available phosphorus contents.Olsen method was the best.?2?The effects of temperature and phosphorus application level on the ion composition,ion activity and phosphate forms in soil solution.The content of DP?water soluble phosphorus?in the soil solution of calcareous fluvo-aquic soil was low.The cation composition of the soil solution was dominated by Ca²⁺,followed by Na⁺,Mg²⁺,K⁺,Fe²⁺,Cu²⁺,and the concentration of Al³⁺,Zn²⁺and Mn²⁺were very low.The concentration of Ca²⁺and DP in the soil solution were significantly affected by the phosphorus application level.The electrical conductivity of the solution increased with the increase of phosphorus application rate.The pH of the soil solution was not significantly affected by the phosphorus application level.The soil pH increased with the rising of temperature,and the electrical conductivity,Ca²⁺and DP concentrations in the soil solution decreased significantly.The results of the ion activity proved the significant effect of temperature on ions in the soil solution.The ion activities of Ca²⁺,Mg²⁺,Al³⁺,Fe²⁺,Cu²⁺,NO₃?and HPO₄²?in soil solution decreased significantly with the rising of temperature,while the activity of F?increased significantly.Correlation analysis showed that the pH of the soil solution significantly affected the ion activity.With the increase of pH,the ionic activity of HPO₄²?in soil solution increased,while that of Ca²⁺decreased.Ca²⁺activity was significantly negatively correlated with activity of HPO₄²?and H₂PO₄?.After the experiment of seven years,the phosphate forms of the soil solution were dominated by the free state and the complex state of inorganic ions.The proportion of DP from high to low were free state HPO₄²?,CaHPO₄?aq?,CaPO₄?,MgHPO₄?aq?,free state H₂PO₄?,NaHPO₄?,and the other forms of phosphorus were very low.With the increase of phosphorus application level,the ratio of HPO₄²?,MgHPO₄?aq?and NaHPO₄?to DP in soil solution decreased significantly,while the ratio of CaHPO₄?aq?and CaPO₄?increased significantly.With the increase of temperature,the ratios of HPO₄²?and H₂PO₄?to DP in soil solution decreased significantly,while the proportion of inorganic complexed CaPO₄?increased.The ratios of CaHPO₄?aq?and MgHPO₄?aq?to DP were not significantly affected by temperature.The results of phosphate solubility equilibria showed that the activities of Ca²⁺and H₂PO₄?were adequate to support the stability of hydroxyapatite and tricalcium phosphate minerals in soils.Phosphate activity in soil solution might be controlled by the solubility of the solid phase of TCP.?3?Effects of temperature and P fertilizer on wheat seedling growth and transformation of soil inorganic phosphorus forms in pot experiment.Taking calcareous fluvo-aquic soil as the research object,the effects of temperature and P fertilizer on wheat seedling growth and transformation of soil inorganic phosphorus forms were studied by pot experiments.The results showed that temperature and phosphorus were important factors affecting wheat growth,and the interaction between them was not significant.The effect of temperature on wheat growth was greater than applying phosphate fertilizer,and 15?was the suitable temperature for wheat growth during seedling stage.Compared with the treatment applied without P at 5?,the application of P fertilizer significantly promoted the growth of wheat;the biomass of wheat shoots and roots increased by 18.2%and 33.3%,respectively;the accumulation of phosphorus in shoots and roots increased by 30.6%and 13.3%,respectively;the root/shoot ratio,plant height,tiller and root activity increased by 3.5%,10.0%,10.5%and70.3%,respectively;At 15?,P application had no significant effect on wheat biomass and tiller,but the phosphorus accumulation in wheat shoots and roots increased by 32.3%and23.8%,respectively;the root/shoot ratio,plant height and root activity increased by 15.6%,2.5%and 32.8%respectively.P application at 25?did not significantly promote wheat growth.P application significantly increased the contents of Olsen-P,Ca₂-P,Ca₈-P,Al-P and Fe-P in each treatments at three temperatures.In non-rhizosphere soil,the content of Olsen-P in the treatments without P decreased significantly with the increase of temperature;treatments applied with P were not significantly affected by temperature.Temperature affected the contents of Ca₈-P,Al-P,Fe-P extremely,and had no significant effect on Ca₂-P content in reatments applied with P or not.The contents of Ca₈-P and Fe-P from high to low were 5?,15?,25?;the contents of Al-P from high to low were 25?,15?,5?.Ca₂-P,Ca₈-P,Al-P and Fe-P could be absorbed by wheat in rhizosphere soil during seedling stage,while Al-P and Fe-P were less effective in wheat than Ca₂-P and Ca₈-P.The difference of pH,O-P and Ca₁₀-P in each treatment was not significant.In short,the temperature mainly affected the growth of wheat by affecting the absorption of P.The application of P fertilizer at low temperature could significantly promote the growth of wheat.High temperature could accelerate the fixation of available phosphorus in calcareous soil.This process could be slowed by phosphate application.