David McRae – IPF Technical Agronomist

Maintaining adequate supply of nutrients during cotton lint development is critical. A large proportion of plant potassium (K) requirements need to be taken up and redistributed from early flower until maturity. Foliar applications can supplement K availability and support plant K sufficiency during periods of high demand or restricted soil supply. However, the effectiveness of foliar K fertilisers varies depending on the form of K and the spray application pH.

Potassium function for fibre development

Potassium’s primary plant function is mainly involved with enzyme activator. It is involved in many processes such as:

  • Photosynthesis
  • Respiration
  • Carbohydrate metabolism
  • Protein synthesis
  • Maintenance of osmotic potential and water uptake


Potassium plays a particularly important role in cotton fibre development, and a shortage will result in poorer fibre quality and lowered yields. K is a major solute that provides turgor pressure necessary for fibre elongation. If K is in limited supply during active fibre growth, there will be a reduction in the fibre turgor pressure, resulting in less cell elongation and shorter fibres at maturity (Oosterhuis 2002).

Figure 1: Early flowering irrigated cotton

Cotton Plant K requirements

High-yielding cotton crops generally require 200 to 250 kg/ha of K. The uptake pattern for nitrogen (N) and K by cotton plants is similar, with approximately 70% occurring after the commencement of flowering. Rates of K uptake range between 3.5 and 5 kg/ha/day during the flowering to cutout period (Oosterhuis 2002). This places a large demand on the soil’s ability to supply plant K requirements during a period of diminishing root growth.

The ability of cotton plants to take up K is affected by the:

  • size of density of the plant’s root system
  • concentration of K in the soil
  • stability of the soil structure (sodicity)
  • amount of water in the soil
  • health of the plant’s roots

Plants use two systems to take up potassium: passive and active. At high soil solution K concentrations, K crosses the root membrane, moving from higher to lower concentration inside the root system. At low K concentration, active transporter systems are needed to transport K inside the root system against the concentration gradient (Ragel et al 2019). Under low K availability conditions, plants expend energy to satisfy crop requirements, and this demand can reduce yields.

Supplementing soil potassium with foliar K during periods of high K demand and reduced root activity can benefit yields. Foliar applications have the advantage of rapid absorption into the leaf and efficient movement to the developing bolls (Chang and Oosterhuis 1995).


Research has shown that foliar K applications are not justified in every situation. However, when high fruit loads, restricted root growth and prolonged cloudy weather associated with tropical storms occur, providing readily available K with foliar fertilisers can help maintain or improve yields.

Maximising foliar K uptake and translocation to bolls

To maximise the uptake of foliar potassium and its movement to cotton bolls, consider these factors:

  • Spray Application: The amount of water, droplet size, and concentration of the spray solution affect how well the potassium is absorbed.
  • Rate and Timing: Aim to apply 3-4 kg/ha of potassium in each application. Cotton plants take up 3.5-5 kg/ha per day, starting 7-10 days after the first flower. Applying 30 L/ha of EASY Liquids® K-FLOW 12 three times, 7 days apart, will add 11 kg/ha of potassium.
  • Spray Solution pH: Many foliar potassium products are alkaline and can cause leaf burn, which harms the plant. Lowering the pH of the spray solution to 4 can improve yields. However, some products are hard to acidify to this level.
  • Potassium Form: Different forms of potassium have varying effects. Research shows that potassium nitrate with a pH of 4 gives the best yield. Other forms like potassium acetate and potassium thiosulfate are less effective (Shafer and Reed 1986, Chang and Oosterhuis 1995).

By considering these factors, you can improve the effectiveness of foliar potassium applications and potentially increase your cotton yields.

Managing K this season

If you are considering applying foliar K in cotton this season, below are some points to consider:

  • Monitor K levels in leaf and petiole samples before and after the start of flowering.
  • Send samples to the Nutrient Advantage® laboratory using the PT4 plant tissue sample code.
  • If the plant tissue results indicate low or marginal K concentrations, consider applying foliar K.

Further information

If Foliar K application is required, contact Bob Moorfield – 0488 067 736 (EASY Liquids Whitton) or Matt Urquhart – 0429 789 298 (EASY Liquids Moree) to discuss application rates or agricultural chemical compatibilities and your requirements.

For further information, please feel free to contact david.mcrae@incitecpivot.com.au or 0477 987 321.

References

Chang M.A. and Oosterhuis (1995). Cotton Response to Foliar Application of Potassium Compounds at Different pH Levels. Better Crops Vol. 79, No. 2.

Howard D.D., Gwathmey C.O. and Sams, C.E. (1998). Foliar Feeding of Cotton: Evaluating Potassium Sources, Potassium Solution Buffering, and Boron. Agronomy Journal. 90:740-746.

Oosterhuis D. M. (2002). “Potassium Management of Cotton.” In Potassium for Sustainable Crop Production. 331–346.

Ragel P., Raddatz N, Leidi E.O., Quintero F.J. and Pardo J.M. (2019). Regulation of K+ Nutrition in Plants. Front. Plant Sci. 10:281. Doi: 10.3389/fpls.2019.00281.

Shafer W.E and Reed D.W. (1986). The Foliar Absorption of Potassium from Organic and Inorganic Potassium Carriers. Journal of Plant Nutrition. 9(2):143-157.