Teagasc is strongly advising tillage farmers to be on the lookout for potash deficiency in spring cereals.
The disorder is quite common in cereal crops following long-term leys, especially where grass silage was intensively cut.
The signs of a potash deficiency include paper-like symptoms on the tips of leaves.
The problem also causes yellowing and chlorosis to the edge and tip of older leaves, with progressive senescence.
Plants may be stunted and exhibit excessive basal tillering.
Significantly, symptoms are not easily distinguished from those resulting from many other causes especially from physiological stress – drought, water-logging, wind, etc.
Potash affects both yield and quality of grain as well as the general health and vigour of the plant.
Cereal crops need as much, if not more, potash than any other nutrient including nitrogen.
Potash is needed in such large amounts because it is the major regulator of solution concentrations throughout the plant.
It controls cell sap content to maintain the turgor of the plant and supports the movement of all materials within the plant.
Potash supply is thus essential for all nutrient uptake by the roots and movement to the leaves for photosynthesis, and for the distribution of sugars and proteins made by the green tissue for plant growth and grain fill.
In the absence of satisfactory potash supply, plants will be poor and stunted, especially in dry seasons.
Physiological stress will be more damaging if potash nutrition is limiting – frost damage will be more severe, waterlogged areas will take longer to recover and plants will wilt earlier and remain flaccid for longer under drought conditions.
Crops will be more susceptible to disease and pests especially where nitrogen and potash availability are imbalanced.
This will result in weaker, sappier growth which will contain a higher concentration of soluble nitrogen compounds and simple carbohydrates providing a readily available food source and attractive focus for pathogens.
Thinner cell walls with less mechanical resistance to predators may also result from potassium shortage.
A review of over 1,000 cereal trials found that, where potash levels were low and out of balance with nitrogen supply, application of potash reduced disease and bacterial infections in over 70% of cases.
Cereals require a balance of nitrogen and potash to obtain full yield response to applied nitrogen.
Careful optimisation of nitrogen is a waste of time if potash supplies are not adequate. Both the level of yield and the shape of the nitrogen response curve are totally altered by potash limitations.
If potash supply is limiting, the uptake and utilisation of nitrogen will be restricted.
If soluble forms of nitrogen remain in the soil and are not taken up, there is increased risk of leaching when through-drainage occurs. Ready availability of both nutrients at peak crop demand helps the uptake of the large requirements of nitrogen and potash.