Phosphate fertilizer conversion method

Transformation of superphosphate in soil: After superphosphate is applied to soil, the main reaction is the dissolution of different components. That is, after fertilization, water gathers to the fertilization point to dissolve and hydrolyze monocalcium phosphate to form a saturated solution of monocalcium phosphate, phosphoric acid and dicalcium phosphate with water, and the reaction is as follows:
At this time, the concentration of phosphorus in the soil solution around the fertilization point can be as high as 10mg/kg-20mg/kg, so that the phosphoric acid continues to diffuse outward. At the point of fertilization, the pH of the saturated solution in the micro-domain soil range can reach 1-1.5. In the process of outward diffusion, it can dissolve iron, aluminum, calcium, magnesium, etc. in the soil, and interact with phosphate ions to form phosphates with different solubility. In calcareous soil, phosphorus and calcium react to form dicalcium phosphate and octacalcium phosphate, and finally most of them form stable hydroxyapatite. In acidic soil, monocalcium phosphate usually reacts with iron and aluminum to form iron phosphate and aluminum precipitation, and then further hydrolyzes into basic iron aluminum phosphate. In weakly acidic soil, monocalcium phosphate is easily adsorbed and fixed by clay minerals. In neutral soil, calcium superphosphate is mainly transformed into CaHPO4·2H2O and dissolved Ca(H2PO4)2, which is the best state for the phosphorus supply ability of crops. CaHPO4·2H2O is weakly acid-soluble and remains at the fertilization point, so the mobility of superphosphate in the soil is very small, with a horizontal range of 0.5cm and a depth of no more than 5cm, and its annual utilization rate is also very low, usually 10%-25%.
Transformation of calcium magnesium phosphate fertilizer in soil: Calcium magnesium phosphate fertilizer can be dissolved under the action of acid secreted by crop roots and microorganisms for absorption and utilization by crops.
Transformation of phosphate rock powder in soil: After phosphate rock powder is applied to the soil, it will gradually decompose under the action of chemical, biochemical and biological factors, changing the original state and transforming into new phosphorus compounds.
The main factors affecting this conversion are soil pH, Ca2+ concentration and H2PO4- concentration. Obviously, acidic conditions are conducive to this conversion of phosphate rock powder, so phosphate rock powder is applied on acidic soil. Fertilizer efficiency is higher.