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Potassium Deficiencies

Potassium (K) is an essential nutrient for plant growth and development. Because large amounts are absorbed from the root zone in the production of most crops and pastures, it is classified as a macronutrient. Potassium has many functions within the plant; including photosynthesis, protein synthesis, water translocation, carbohydrate metabolism for energy production, stomata control, pest and disease resistance and improving the cold tolerance of plant tissue.

Factors that affect potassium uptake


Higher soil moisture usually means greater availability of potassium. Both drought stress and excess moisture reduce the uptake of potassium.


Air is necessary for root respiration and potassium uptake. Root activity and subsequent potassium uptake decrease as soil aeration decreases.


Root activity, plant functions, and physiological processes all increase as soil temperature increases. This increase in physiological activity leads to increased potassium uptake. Potassium uptake is reduced at low soil temperatures.

Potassium level

If soil potassium levels are low, plant uptake levels will also be low.


Symptoms of a deficiency typically appear on the older leaves of a plant, either as scorching or spotting along leaf margins. Potassium deficient crops will grow slowly, have poorly developed root systems, have small leaves, stalks are often weak, lodging is common, seeds and fruit pieces can be shriveled and small and plants have limited resistance to pest and disease attacks.

Lucerne / pasture / legumes

White or yellow dots form along leaf margins.


Reduced internode spacing and scorching of the outer edge of the leaf.


Necrosis on leaf tips and margins, interveinal chlorosis of older leaves.


Old leaves become chlorotic and will eventual fall off.


Stunted and wilted plants, chlorosis at tips and along leaf margins.


Leaf edges become scorched and then broken with shrivelled non uniform seeds.

Management tools

A soil test for potassium is the best management tool for predicting the amount of potash needed in a fertilizer program. Available potassium in soils is estimated by measuring the total of solution K (water = soluble K) and exchangeable K. Plant tissue tests can also be used to assess how the crop and/or pasture is extracting potassium from the soil environment.


The Solution to Potassium Deficiency in Pasture, Crop and Fodder Production. To complement BioAg’s existing range of solid fertilisers, PotPhos® (9%P, 10%K, 5%S & 26%Ca) has been developed for situations where phosphorus, potassium, sulphur and calcium are required.

PotPhos combines the benefits of BioAgPhos®, a highly reactive phosphate rock source and potassium sulphate, a biologically friendly potassium source.

The product was formulated for the high rainfall zones in Victoria, Tasmania and New South Wales, where potassium deficiency reduces pasture, crop and fodder production.

PotPhos is a well-balanced fertiliser for both autumn and spring application in high rainfall environments, but it is also well suited to irrigated fodder production in the warmer climates.