Soil Test Recommendation Calculator

Work out soil test recommendation instantly with clear inputs, formula shown and shareable results.

About Soil Test Recommendation Calculator

Targeted-yield fertiliser recommendation works from a nutrient balance: the crop's total requirement is target yield x uptake per tonne, the soil supplies roughly half of the available pool measured by the test, and the shortfall must be met by fertiliser divided by its use efficiency. Nitrogen efficiency is typically 30-50%, phosphate 15-25% and potash 50-70%.

Formula

Targeted yield equation

Fertiliser dose = (target yield x uptake per tonne - 0.5 x soil test value) / fertiliser use efficiency

Worked example

With the default values below, Soil Test Recommendation Calculator returns Recommended Fertiliser Dose of 252.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Soil Test Valueminimum 0 kg/ha available: 18 kg/ha available
Target Yieldminimum 0.1 t/ha: 5 t/ha
Nutrient Uptake Per Tonne Of Yieldminimum 0.1 kg/t: 22 kg/t
Fertiliser Use Efficiencyaccepts 1–100 %: 40 %

Results

Recommended Fertiliser Dose: 252.50
Total Crop Nutrient Requirement: 110.00
Nutrient Supplied By Soil: 9.00
Nutrient Deficit: 101.00

Step by step

1Values used
2Targeted yield equation
3Recommended Fertiliser Dose= 252.50
4Total Crop Nutrient Requirement= 110.00
5Nutrient Supplied By Soil= 9.00
6Nutrient Deficit= 101.00

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.

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

Frequently Asked Questions

What uptake figures should I use?

Roughly 20-25 kg N, 10-12 kg P2O5 and 25-30 kg K2O per tonne of cereal grain including straw. Vegetables and fruit differ substantially, so use a crop-specific table.

Why only credit half the soil test value?

The extractant measures a pool that is only partly accessible in a single season. State recommendation systems fit an empirical soil-contribution coefficient, commonly 0.4-0.6, from field trials.