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Nitrogen, Phosphate and potash

The Effects of Nitrogen

Raising the level of N application up to a certain point, increases tuber yields. Higher applications delay the development of tubers. These tubers end up with a watery texture and of low cooking quality. The foliage of these plants with excessive nitrogen is very susceptible to blight and also delay potato set and maturity of the potato.

The Effects of Phosphorus

Phosphorus encourages early rooting as well as later maturity, harder skins, and may reduce tuber blight. P can increase dry matter.

The effect of Potash

Potash increases tuber size, but excess K (even excess sulphate of potash) may slightly reduce dry matter content. The use of sulphate of potash instead of muriate of potash (chloride) will help to increase tuber dry matter.

Recommended Fertiliser Rates

Fertiliser application should be based on a recent soil test. The generally recommended range of fertiliser application for maincrop ptatoes is as follows:

Fertiliser should be applied to the seed bed. Potatoes poorly utilise phosphate due to its root structure so a well prepared seed bed is essential for good uptake.

Table 42: The nutrient requirement kg/ha (units/acre) for 15t/ha (6t/acre) dry matter main potatoes are:

Soil Fertility (P & K Index)P kg/ha (u/ac)K kg/ha (u/ac)
Poor (1) 125 (100) 305 (244)
Deficient (2) 100 (80) 245 (196)
Moderate (3) 75 (60) 185 (148)
High (4) 50 (40) 120 (96)

Note: Where soil P test is above 15 mg/l no fertiliser P is necessary.

Further details on potato nutrition can be found on the Teagasc website at:


Details of general soil fertility can be found on the Teagasc website at: