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Nutrient conversion and product dose

From the recommended dose in oxide form to the element and to the product you buy.

Pre-sizing and estimating tool: the results do not replace a design, calculation, or report signed by a qualified professional, nor verification against the applicable standards.

Preliminary estimateRevision 12/11/2026
Doses as oxide (kg/ha)
Commercial product (for phosphorus)

The conversion uses atomic masses: P = P₂O₅ × 0.437; K = K₂O × 0.830; Ca = CaO × 0.715; Mg = MgO × 0.603. The product is what you buy, with the guaranteed content on the package.

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—Elemental phosphorus (P) of the dose
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Doses in both forms

Each nutrient in oxide form and in elemental form, in kg/ha.

Tap the chart to see the values.

Commercial product by P₂O₅ dose

Amount of product needed to deliver each P₂O₅ dose, with the content you entered.

Tap the chart to see the values.

What if the data changes?

Drag the controls to simulate data different from what you entered (from 30% less to 30% more) and watch the result change instantly.

Tap the chart to see the values.

How much common fertilizer delivers your dose

Amount of product needed to deliver the doses you entered, using typical contents of common fertilizers. Check the content on the label.

Step by step with your numbers

The calculation done in steps, with the values you entered.

    The calculation memo gathers this page's inputs, results, equations, assumptions, and references, with fields for project, responsible person, and review. The full report also includes the charts and interpretations, in color. In the print window, choose Save as PDF.

    How to use

    Enter the P₂O₅, K₂O, CaO, and MgO doses in kg/ha as they appear in the fertilization recommendation, and the P₂O₅ content of the product you will buy. The calculator shows each element in its corresponding form and the amount of product.

    Hypothetical example

    Dose of 120 kg/ha of P₂O₅, 80 of K₂O, 60 of CaO and 20 of MgO, with a product at 41% P₂O₅.

    P = 120 × 0.437 = 52.4 kg/ha; K = 80 × 0.830 = 66.4 kg/ha; Ca = 60 × 0.715 = 42.9 kg/ha; Mg = 20 × 0.603 = 12.1 kg/ha.

    Product = 120 ÷ 0.41 = 293 kg/ha.

    Precautions

    • The product entered must be the one on the label or invoice; the actual content may vary from the guaranteed content.
    • This calculation does not consider the nutrient use efficiency in the soil. That depends on the soil analysis.
    • The factors are stoichiometric: P is not P₂O₅, but the fraction of P in the oxide.

    Method, assumptions, and references

    Equations used

    P = P₂O₅ × 0.437
    K = K₂O × 0.830
    Ca = CaO × 0.715
    Mg = MgO × 0.603
    Product (kg/ha) = nutrient dose (kg/ha) ÷ nutrient content in the product

    Assumptions and limits

    • Stoichiometric factors: each element is the mass fraction of the corresponding oxide.
    • The product content is the guaranteed value on the label; the actual analysis may differ.
    • Does not consider the nutrient's use efficiency in the soil or application losses.

    Standards and technical documents

    • Malavolta, E. Elements of Plant Mineral Nutrition. São Paulo: Agronômica Ceres, 1980.
    • Raij, B. van et al. Recomendações de adubação e calagem para o Estado de São Paulo. IAC Technical Bulletin 100. Campinas: IAC, 1997.

    Frequently asked questions

    Why does phosphorus appear as P₂O₅?

    Because this is how fertilizers and fertilization recommendations state the content. Elemental phosphorus is about 44% of P₂O₅.

    How do I use the result?

    Compare the product amount with the fertilization recommendation and with what you have in stock; the product is what you buy and apply.

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