DAP Requirement Calculator

Work out dap requirement instantly with clear inputs, formula shown and shareable results.

About DAP Requirement Calculator

Di-ammonium phosphate is 18-46-0, so it is sized on the phosphate requirement: DAP = P2O5 need / 0.46. It also delivers 18% nitrogen, and that nitrogen must be credited against the N plan by deducting the equivalent urea, otherwise the crop is over-fertilised with N.

Formulas

DAP quantity

DAP (kg) = P2O5 required / 0.46

Nitrogen credit

N supplied = DAP x 0.18; urea deduction = N supplied / 0.46

Worked example

With the default values below, DAP Requirement Calculator returns DAP Required of 130.43. Change any input above and every figure here is recalculated in your browser.

Inputs used

Phosphate Requiredminimum 0 kg P2O5: 60 kg P2O5
P2O5 Content Of DAPaccepts 1–100 %: 46 %
Nitrogen Content Of DAPaccepts 0–100 %: 18 %
Bag Sizeminimum 1 kg: 50 kg

Results

DAP Required: 130.43
Nitrogen Supplied By DAP: 23.48
Bags Required: 2.61
Urea That Can Be Deducted: 51.04

Step by step

1Values used
2DAP quantity
3Nitrogen credit
4DAP Required= 130.43
5Nitrogen Supplied By DAP= 23.48
6Bags Required= 2.61
7Urea That Can Be Deducted= 51.04

Assumptions and limits

The result is derived only from the 4 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.
Phosphate lost in runoff drives eutrophication of lakes and rivers. Do not exceed soil-test recommendations and keep applications away from watercourses.

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

Phosphate lost in runoff drives eutrophication of lakes and rivers. Do not exceed soil-test recommendations and keep applications away from watercourses.

Frequently Asked Questions

When should DAP be applied?

As a basal dose placed near the seed row at sowing. Phosphate moves very little in soil, so broadcasting it on the surface leaves much of it out of reach of young roots.

Can single super phosphate replace DAP?

Yes — SSP is 16% P2O5 plus sulphur and calcium, so you need about 2.9 times the weight of DAP for the same phosphate, and the nitrogen credit disappears.