How to calculate the amount of fertilizer applied to soil testing formula

At present, formula fertilization has become a hot spot in agricultural production. In general, the recommended application rate for the soil testing formula fertilization table is the amount of purity nitrogen, P205 (phosphorus pentoxide), and K2O (potassium oxide). Due to the different effective content of various fertilizers, it is difficult for farmers to accurately grasp the amount of fertilizer used in the production process. Assume that the recommended amount of fertilizer for a piece of land is 8.5 kg per mu of pure nitrogen, 4.8 kg of P2O5, and 6.5 kg of K2O.
The calculation method of single fertilization is: (recommended fertilization amount of effective fertilizer) × 100 = amount of fertilization. The calculation found the following results: the application of urea (the nitrogen content of urea is generally 46%) should be (8.5 ÷ 46) × 100 = 18.4 kg; the application of superphosphate (the content of P2O5 in superphosphate is generally 12% - 18%) should be (4.8÷12)×100=40kg; the application of potassium sulfate (the content of K2O in potassium sulfate is generally 50%) should be (6.5÷50)×100=13kg.
The amount of compound fertilizer applied should be calculated with the fertilizer with the least amount of recommended fertilizer, and then the other two fertilizers should be added. If the nitrogen, phosphorus and potassium content of a certain compound fertilizer bag is 15:15:15, then the compound fertilizer should be applied to the plot: (4.8÷15)×100=32kg. Because the proportion of nutrients in compound fertilizer is fixed, it is difficult to meet the demand for various nutrients in different soils of different crops. Therefore, it is necessary to add elemental fertilizer to supplement, and the calculation company is: (recommended fertilization amount - applied fertilizer amount), ready to apply fertilizer Effective content = the amount of fertilizer added. The plot was applied with 32 kg of compound fertilizer with 15% NPK content, which was equivalent to 32×15=4.8 kg of pure nitrogen applied to the soil, and 4.8 kg of P2O5 and K2O.
According to the recommended fertilizer application amount of pure nitrogen 8.5kg, K2O6.5kg, it is necessary to increase the application: urea (8.5-4.8) ÷ 46% = 8kg, potassium sulfate (6.5-4.8) ÷ 50% = 3.4kg.
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