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).
PDA Straw Calculator notes
This Calculator gives best estimates of phosphate and potash contents of a number of straws as harvested. These figures provide a useful guide, but the actual values for specific crops may vary. For example, the potash (but not the phosphate) contained in the straw may be reduced if there is appreciably more rain than average between the onset of senescence and baling.
On average the amount of straw produced per hectare is in proportion to the grain yield, so the nutrient content per hectare of straw can be estimated by multiplying the grain yield by standard factors for phosphate (P2O5), for potash (K2O) which take into account the ratio of straw to grain yield, where actual figures are not known.
When straw is sold off farm, it is useful to know the cost of the probable quantity of fertiliser nutrients in each tonne of straw to make a more informed decision on the value of baling. This calculator aims to simplify this calculation. Although this gives a financial value to the nutrients removed in straw, it does not take into account other factors such as soil structural remediation that may be required from baler wheelings, or the cost of organic matter removal where straw is not returned.