Screening And Mechanism Research Of Phosphate Fertilizer Synergist

Phosphate fertilizer has poor mobility in calcareous soil,easy to be fixed,and has low utilization rate.This article intends to screen out suitable synergists through indoor cultivation experiments and add them to phosphate fertilizers to reduce and inhibit the soil’s solidification rate of phosphorus and increase the utilization rate of phosphate fertilizer.There are 8 materials includingγ-polyglutamic acid,lignin,malonic acid and sulfur powder are used as synergists,monoammonium phosphate is used as phosphorus source,and the fluvo-aquic soil in Zhengzhou area,cinnamon soil in Zhoukou area and sandy soil in Changtu area were used as test soil,the effect of different synergists on the effective phosphorus content of the soil and the suitable ratio of synergist and monoammonium phosphate were studied through 90-day indoor culture experiment.Inorganic phosphorus classification method and phosphorus adsorption experiment were used to study the influence of synergist on inorganic phosphorus form and phosphorus adsorption characteristics.By measuring the physical and chemical properties of some soils,the reasons why synergists affect phosphorus fixation and adsorption characteristics were analyzed.The effect of synergist on phosphorus availability of three calcareous soils was studied through a90-day indoor culture experiment,and the reasons for this difference were discussed.The main research conclusions are as follows.Compared with the single application of monoammonium phosphate（NH₄H₂PO₄）,the soils treated with 8 synergists increased the phosphorus availability by 47.7%,17.8%,13.2%,8.8%,5.6%,5.5%,12.8%and 5.5%,respectively,of whichγ-polyglutamic acid had the best effect in improving the effectiveness of phosphorus;different additions ofγ-polyglutamic acid,lignin,malonic acid and sulfur powder mixed with monoammonium phosphate（NH₄H₂PO₄）can all improve the effectiveness of phosphate fertilizer.The addition amount of synergist and monoammonium phosphate was 0.5 g:0.5 g had the best effect.By the classification of the soil inorganic phosphorus content,it was found that the addition of synergists can reduce the rate of Ca₂-P conversion to Ca₈-P,which was the reason for the increase in the availability of soil phosphorus.Phosphorus adsorption kinetics experiments showed that the soils treated withγ-polyglutamic acid,lignin,sulphur powder and malonic acid had a change in the adsorption rate of phosphorus compared with CK.Within 0～1 h from the beginning of the adsorption kinetics experiment,the adsorption rate of phosphorus decreased by22.7 mg·kg^-1·h^-1,9.0 mg·kg^-1·h^-1,9.1 mg·kg^-1·h^-1and 6.79 mg·kg^-1·h^-1,indicating that the addition of the synergist can reduce the phosphorus adsorption rate in the soil.The results of isothermal phosphorus adsorption showed that the maximum phosphorus adsorption capacity in the treatment group supplemented with four synergistic agents decreased by 67.3 mg·kg^-1,47.8 mg·kg^-1,13.2 mg·kg^-1 and 37.0 mg·kg^-1,respectively,compared with CK,indicating that the addition of synergistic agents could reduce the adsorption of phosphorus in soil.By analyzing the physical and chemical properties of the soil,it was found that the addition of synergist reduced the content of calcium carbonate（CaCO₃）in the soil.Therefore,it was concluded that the synergist could reduce the probability of soil phosphorus fixation and improve the effectiveness of phosphorus by reducing the content of calcium carbonate in the soil.Adding 4 kinds of synergists can increase the availability of phosphorus in fluvo-aquic soil,cinnamon soil and sand soil,but their effects are not the same.Taking the three soils treated withγ-polyglutamic acid as an example,on the 90th day of cultivation,the effectiveness of phosphate fertilizer was increased by 57.9%,26.8%and 10.1%,respectively,compared with the single application of phosphate fertilizer.The results of redundancy analysis showed that the main reason for the difference ofγ-polyglutamate effect was the difference of the contents of calcium carbonate and soil organic matter（SOM）in the three soils.