ARCHIVE: Fertiliser Manual (RB209)

Calculating the amount of fertiliser to apply

The content of each nutrient in a fertiliser is given as a percentage of N, P2O5 and K2O.


Winter wheat grown on a P Index 2, K Index 1 soil and expected to yield 8 t/ha grain requires 200 kg N/ha, 65 kg P2O5/ha and 114 kg K2O/ha. A 20: 10: 10 NPK compound fertiliser is available and 100 kg contains 20 kg N, 10 kg P2O5 and 10 kg K2O. Applied at 1000 kg/ha this fertiliser will supply 200 kg N/ha, 100 kg P2O5/ha and 100 kg K2O/ha.

The surplus 35 kg P2O5/ha can be allowed for later in the rotation.

The deficit of 15 kg K2O/ha can be ignored.

Metric to imperial conversion tables are given in Appendix 8. If applying liquid fertilisers, manufacturers can supply tables which convert kg/ha of nutrient to litres/ha of product.


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