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LCF Australia

Nutrient guide

Potassium (K)

Controls water use and plant strength. Often adequate on heavier soils, but short on many light, sandy soils.

What potassium does

Potassium regulates water movement in the plant, including how leaf pores open and close. It supports stem strength, disease resistance and grain fill.

Where it is often short

Many heavier Australian soils hold good reserves of potassium. Shortages are more common on light, sandy soils, in higher-rainfall areas, and in paddocks that have been cut for hay for several years, because hay removes large amounts of potassium.

Signs of deficiency

Older leaves yellow and then brown from the tips and margins. In clover, small pale spots appear around the leaf edges and join up. Crops may lodge more easily.

Testing and sources

  • Soil tests such as Colwell K or exchangeable potassium show whether reserves are low.
  • Common sources include muriate of potash (potassium chloride) and sulphate of potash, which also supplies sulphur.
  • Many compound fertilisers include potassium alongside nitrogen and phosphorus.

Crop guides

What potassium deficiency looks like

Photos of deficiency symptoms. Where we do not yet have a suitable photo, we will add our own trial photo. Symptoms vary with crop, variety, soil and season.

  • Potato leaves with brown, scorched and curled margins while the centres of the leaves stay green
    Potassium deficiency in potato: older leaves scorch and brown from the margins inwards. Photo: Simranpreetsidhu, CC BY-SA 4.0, via Wikimedia Commons.
  • Rows of dry bean plants in a trial, with one variety strongly yellowed and the neighbouring variety greener
    Potassium deficiency in dry bean, a pulse: two varieties on the same low-potassium soil, one showing severe yellowing. Photo: Alandmanson, CC BY-SA 4.0, via Wikimedia Commons.

Photos may show other crops with the same symptom. Full credits: Image credits.

How LCF products fit

LCF Australia supplies compound fertilisers made by our manufacturing partner Lardmee (LDM), including Urea Plus and zinc and manganese sulphates, on enquiry. We also supply the Field Spears soil testing kit, which reads soil N, P, K and pH in the paddock. Which product suits, how much and when depends on the soil, the crop, the season and how you apply it.