Potash is a key nutrient for potato crops, impacting on the yield and quality of tubers, as well as the general health of individual plants.

It is involved in regulating the amount of water in the plant, because in the absence of sufficient potassium, crops do not use water efficiently, according to the Potash Development Association (PDA).

In addition, adequate potash (potassium or K) levels in the plant help it to withstand water stress during periods of drought.

As an element, K plays a vital role in maintaining the turgidity (rigidity) of plant cells, the PDA has said.

Because of its importance in turgor maintenance, K is essential in obtaining maximum leaf extension and stem elongation.

This helps to achieve rapid ground cover while maximising interception of sunlight, and therefore the rate of growth in the critical early periods of the growing season, which is of particular importance for spring sown crops such as potatoes.

All of the aforementioned issues are addressed in a detail in a potato crop advisory update recently published by PDA.

Ensuring an adequate supply of K is critically important for all crops because the plant nutrient plays a vital role in the movement of sugars, produced in the leaf by photosynthesis.

Specifically, where potatoes are concerned, these sugars are transported to the tubers where they are are converted to starch.


Potassium also contributes to various aspects of tuber quality that may be vital for a marketable sample. The balance between nitrogen (N) and K supply is of particular importance for this crop.

The PDA has stated that it is well established that crops deficient in potash are less able to handle stress caused by drought, waterlogging, frost, heat, or wind.

However, it appears that there is no advantage to be gained from applying larger amounts of K than those justified for yield and replacement requirements, unless aiming to build up soil reserves.

While yield variation will occur according to the growing conditions in different years, smaller yields in ‘poor’ years can be minimised by ensuring an adequate potash supply.

Potash shortage has a number of outcomes. These include: low yield; poorer marketable quality; thinner cell walls and less lignifications; weaker stems; reduced resistance to disease; lower starch content of the tubers; and a reduced response to N.

Potatoes take up more potash than many other arable enterprises. In the six weeks after plant emergence, the crop will take in at least two thirds of the total K uptake.

During peak vegetative growth, potatoes may require 10kg K2O/h/day from the soil.

Main crop potatoes contain the maximum quantity of potash in late July to early August, in both tubers and haulm. This figure can exceed 500kg of K2O/ha for high yielding crops.