Potash - stress relief for crops

There is increasing evidence that an adequate potash supply will help reduce crop stress caused by drought, chilling, high light intensity, heat and deficiencies of other nutrients. These stresses can result in oxidative damage to the plant from 'reactive oxygen species' (ROS) free radicals, and production of these damaging ROS can be greatly reduced by a satisfactory potash status in the plant.

Adequate supply of potash is essential to crop yield and quality, both of which are dependent on the role of potassium in maintaining the general health of the plant. When potash (K) supply is low, plants can become very sensitive to environmental stresses. The chart on the right shows photosynthesis rates in pot-grown cotton plants declining with increasing K deficiency, and this effect is more marked when atmospheric CO₂ levels are raised.
Ref: Cakmak, I. (2005). J. Plant Nutr. Soil Sci. 168, 521-530.

Frost damage:

Increasing the supply of potash has been shown to improve the resistance to cold damage in frost-sensitive plants. In potatoes and oilseed rape the yield reduction and increased leaf damage caused by frost can be significantly reduced by increased potash supply.

Drought:

Crops suffering from drought have an increased internal potassium demand and an inadequate potash supply will make a loss of yield in drought conditions more likely. It is particularly important that non-irrigated crops have a sufficient availability of K from the soil so that they are better able to resist damage from even temporary periods of drought (Fig. from Calmak, 2005).

High temperatures and extreme weather:

If recent indications of greater extremes in the weather become more frequent, it will be increasingly important to maintain an adequate soil potash status and therefore crop K supply to guard against potential poor crop performance. High light intensities associated with other stress factors can rapidly cause leaf chlorosis, often seen as leaf spotting.

Aphid multiplication:

Recent work in the USA has shown a significant effect of low K status in soybeans in increasing the reproductive rate and population growth in aphids. When K is deficient the synthesis of high molecular weight compounds (proteins, starch, cellulose) is impaired so that low molecular weight compounds such as sugars and amino acids accumulate; these are a good source of nutrition for aphids and plant pathogens. Although this specific work was carried out in the USA, several other authors have reported similar effects on aphids and other sap-feeding insects where N and K relationships are imbalanced.
Ref: Myers, S.W. and Gratton, C. (2006). Environmental Ecology, 35(2), 219-227.

Conclusion:

It is clear that a wide range of stress factors can have a much more serious effect on crop plants when the potassium supply is inadequate than when K availability is satisfactory. When seen, many of the symptoms, such as leaf spotting, are considered to be the normal result of 'stress', but there is sufficient evidence to suggest that in many cases they can be indicators of potash deficiency in the field. Whether or not potash is implicated can easily be checked by plant and soil analysis, but it must be remembered in the case of soil analysis that however small the area which is to be sampled, at least 16 cores must be taken and bulked together to provide a representative sample for analysis and to ensure a meaningful result.

For further information please contact:
PDA info@pda.org.uk
Potash Development Association

update: May 2007