Effect on cereal yield components

Adequate available potash is essential for the production of high-quality marketable grain with good specific weight and well filled grains. A shortage will result in premature ripening with significantly lower individual grain size and weight, and will also prevent some potential grain sites from developing, thus reducing the number of grains per ear.

	Level of potash
	Deficient	Intermediate	Sufficient
Days from flowering to ripening	46	68	75
Grain number per ear	36	38	43
1000 grain weight (g)	17	33	34

Effect on straw strength

Potash enhances the development of strong cell walls and therefore stiffer straw. Lodging is affected by obvious factors such as variety, nitrogen rate and weather, but low potash levels also increase the risk of lodged crops with the associated loss of yield and quality. The effect can be as dramatic as a lack of growth regulator in some circumstances as illustrated in the photograph above.

Effect on plant vigour, health and stress resistance

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 1000 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.