This Calculator gives guide results only; the effects of applications of fertilisers or manures must be checked by soil analysis.
Large single applications of phosphate must be made with care to avoid losses to watercourses through surface run-off or via cracking clay soils.
It is recommended that deficiency-correcting applications of phosphate should not usually exceed 100 kg P2O5/ha per year.
Phosphate and potash applications made to correct deficiencies should be incorporated fully into the topsoil.
Potash should always be applied with care to avoid high concentrations close to seeds or seedlings. Ideally a major portion of corrective dressings of potash should be ploughed down.
Guidance on soil sampling is given in PDA leaflet 24; recommendations for sampling non-ploughed soils should be noted.
The current year application value does not take account of soils above target Index; on such soils no dressing may be required.
The soil nutrient values used (mg/litre) are those derived by Olsen's method for P and ammonium nitrate exchange for K. The Index numbers are those used in the AHDB Nutrient Management Guide (RB209) (2017).