Identification Of Naturally Occurring Phosphate Minerals And Mechanism Of Phosphate Activation In Calcareous Soils With Long-Term Heavy Application Of Phosphate Fertilizers

In agricultural production,the applied phosphorus fertilizer cannot be fully absorbed and utilized by crops,and most of the phosphorus will accumulate in the soil due to the role of soil fixation,which will lead to the accumulation of a large amount of accumulated phosphorus in the soil in the long term,which not only reduces the utilization rate of phosphate fertilizer,wastes the limited phosphorus resources,but also easily causes serious environmental problems.The aim of this study was to verify the formation of stable phosphate crystal mineral in typical calcareous fluvo-aquic soil with long-term and large application of phosphate fertilizer,and to clarify the correlation between phosphate mineral species,approximate formation time and the solubility of phosphate in soil and phosphorus classification.Ten soil samples representing the three utilization modes were collected from the forest land,grain cultivated land and vegetable greenhouses in Shouguang city,Shandong province.To investigate the effects of coated phosphate fertilizers and plant inducers?Paecilomyces variotii?metabolites on maize yield and phosphorus utilization rate in fluvo-aquic soil and its mechanism for activating phosphorus.The morphological transformation and final products of phosphorus in calcaric soil in Shouguang vegetable field,grain cultivated land and forest land were studied,and the method and mechanism of efficient utilization of phosphorus were studied by means of maize pot experiment.The main research contents and results are as follows:?1?Carbonate-removed soil samples were divided into sand,clay and silt.X-ray diffraction was used to identify the soil.No obvious diffraction peaks were found in the clay and sand of all samples.Obvious diffraction peaks matching the peaks of apatite were found in silt grains of vegetable soils that had been fertilized for more than 20 years and a 10²0 years period.However,in uncultivated and cultivated vegetable soils with short cultivation time and long-term cultivation The crop soils have not been found in the presence of crystalline apatite.The results show that phosphorus application is the direct cause of the formation of phosphorus minerals in the soil,and the crystalline phosphorus minerals mainly exist in silt grains due to the adsorption and fixation of the soil itself,and the formation of phosphorus minerals is a long-term process.Through soil cultivation,the soil solution was extracted without phosphorus and66.8 mg kg^-1 P control group,and the activities of Ca²⁺and H₂PO₄^-calculated by the MINTEQ3.1 chemical equilibrium model were sufficient to support the vegetable soil.Stability of hydroxyapatite?HA?,fluoroapatite?FA?,tricalcium phosphate?TCP?and octacalcium phosphate?OCP?minerals,but octacalcium phosphate?OCP?in uncultivated soil and agricultural soil Unstable.The classification of soil inorganic phosphorus indicates that Ca₈-P accounts for the main position in vegetable soils with a large amount of phosphorus applied for a long time,while the proportion of Ca₁₀-P in grain farming and forest land is much higher than that in vegetable fields,and the proportion of Ca₂-P Low level.Therefore,long-term large-scale application of phosphate fertilizer will lead to the formation of stable phosphorus minerals in calcareous soil.?2?Under the condition of equal phosphorus,CP can significantly increase the yield by5.89%¹0.07%,improve the utilization rate of phosphate fertilizer by 6.83⁸.14 percentage points;P+PGR can significantly increase the production by 7.46%⁹.31%,and the utilization rate of phosphate fertilizer by 4.79⁶.16.The percentage of phosphatase activity in rhizosphere soil increased by 17.65%²7.90%;CP+PGR significantly increased production by 7.78%¹6.28%,and the utilization rate of phosphate fertilizer increased by 8.76¹4.00 percentage points.When phosphorus is reduced by 20%,the coating and spraying attractant have synergistic effect.Compared with CP and P+PGR treatments,CP+PGR significantly increased rhizosphere soil phosphatase activity by 21.81%and 11.66%,pyruvate phosphobiskinase activity by 33.33%and 14.28%,and AGPase enzyme activity by 75.47%and 47.62%.The effective phosphorus content of the soil was 33.66%,19.45%,14.99%,and 26.05%at 58 and103 days after sowing.The difference between the yield and conventional phosphorus treatment was not significant,and weight loss and stable yield were achieved.Under the conditions of this study,coated diammonium phosphate combined with an attractant can increase the activity of maize phosphatase in the rhizosphere of key growth stages,enhance the supply of soil phosphorus,increase the photosynthetic enzyme and amylase activity of the leaves,and then improve the utilization rate of phosphate fertilizer.Under the condition of reducing phosphorus by 20%,the production remained stable.In summary,the conversion of applied phosphate fertilizer in calcareous soil is mainly based on the calcium-phosphorus system,and the presence of apatite was directly identified by XRD in three calcareous soils with large amounts of phosphorus applied for a long time.The final reaction product in the soil is a stable phosphate mineral.The phosphate solubility map reveals that the phosphate form in the soil is controlled by the solubility of the phosphate,and the soil phosphorus classification data shows that the phosphate fertilizer will be quickly converted to phosphoric acid after being applied to the soil.Stable phosphorus forms such as octocalcium,and the application of phosphorus will promote the transformation of phosphorus forms in the soil;coated phosphorus fertilizers control the slow release of nutrients to avoid the rapid transformation of phosphorus fertilizers into the phosphorus form that cannot be directly utilized by plants such as Ca₈-P after being applied to the soil.Plant lure can reduce soil pH,and at the same time promote plant secretion of phosphatase to activate soil phosphorus,increase soil effective phosphorus content,the utilization rate of phosphorus fertilizer in the season,reduce the fixed conversion of soil phosphorus,reduce the amount of phosphorus fertilizer application,and save phosphorus resources and prevention of environmental pollution risks from agricultural activities.