Fertilizer Requirement

Free Fertilizer Requirement calculator with clear step-by-step results.

About Fertilizer Requirement

Fertiliser rates are specified as kilograms of nutrient per hectare, but products are sold as bulk material containing a percentage of that nutrient. Subtracting the soil's own supply, dividing by nutrient content and again by spreader efficiency converts an agronomic target into the product rate to actually set on the machine.

Formulas

Nutrient deficit

Deficit = target rate - soil supply

Product rate

kg product/ha = deficit / nutrient content / application efficiency

Worked example

With the default values below, Fertilizer Requirement returns Product application rate of 229.5. Change any input above and every figure here is recalculated in your browser.

Inputs used

Area to fertiliseminimum 0.01 ha: 4 ha
Target nutrient rateminimum 0 kg/ha: 120 kg/ha
Nutrient already supplied by the soilminimum 0 kg/ha: 25 kg/ha
Nutrient content of the productaccepts 1–100 %: 46 %
Application efficiencyaccepts 30–100 %: 90 %
Product priceminimum 0 $/t: 450 $/t

Results

Product application rate: 229.5 kg/ha
Total product to buy: 917.9 kg
Nutrient the crop needs from fertiliser: 95.0 kg/ha
Total fertiliser cost: $413.04

Step by step

1Values used
2Nutrient deficit
3Product rate
4Product application rate= 229.5 kg/ha
5Total product to buy= 917.9 kg
6Nutrient the crop needs from fertiliser= 95.0 kg/ha
7Total fertiliser cost= $413.04

Assumptions and limits

The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Nutrient application is regulated in many regions, with limits on rates, timing and proximity to watercourses. Follow a soil test and any applicable nutrient management plan or legal restriction.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Nutrient application is regulated in many regions, with limits on rates, timing and proximity to watercourses. Follow a soil test and any applicable nutrient management plan or legal restriction.

Frequently Asked Questions

Where does soil supply come from?

A soil test, plus mineralisation from organic matter and any residues from a previous legume crop. Ignoring it is the most common cause of over-application.

Why divide by application efficiency?

Spreading is never perfectly uniform, and some nutrient is lost to volatilisation or immobilisation before the crop uses it. The efficiency term compensates for both.