Fertiliser application rate calculator
A fertiliser bag is labelled with the percentage of each nutrient, so the product rate is the nutrient target divided by that share.
kg N/ha
%
%
%
Product rate
750.0kg/ha
- Rate per square metre
- 75.00 g/m2
- Product for the whole area
- 0.750 tonnes
- Phosphate applied
- 75.0 kg P2O5/ha
- Potash applied
- 75.0 kg K2O/ha
- Cost per hectare
- 337.50
- Total cost
- 337.50
- Cost per kg of nitrogen
- 2.250
Show the working
- Area = 1
- Nitrogen target = 150
- Nitrogen in the product = 20
- Phosphate in the product = 10
- Potash in the product = 10
- Price per tonne = 450
- Product rate = 150 / (20/100) = 750
- Product for the whole area = 750 * 1 / 1000 = 0.75
- Phosphate applied = 750 * 10/100 = 75
- Potash applied = 750 * 10/100 = 75
- Cost per hectare = 750 / 1000 * 450 = 337.5
- Total cost = 337.5 * 1 = 337.5
- Cost per kg of nitrogen = 20 > 0 ? 450 / 1000 / (20/100) : 0 = 2.25
- Rate per square metre = 750 / 10 = 75
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- product rate = nutrient target / nutrient fraction
NPK labels give nitrogen as N but phosphorus as P2O5 and potassium as K2O, which are oxides rather than elements. Multiply P2O5 by 0.436 for elemental P and K2O by 0.830 for elemental K.