Role of potassium in frost resistance

February 2021

With the recent cold conditions experienced throughout the UK it is worth considering the impact of nutrition on plant tolerance to cold. The role of K in protecting crops against frost damage is widely recognised, however the detail behind the mechanisms may not be so clearly understood.

When potash is deficient in plants, the stomatal activity is inhibited resulting in poor control over gas exchange, impairing photosynthesis and water control, making plants more susceptible to stresses from drought, frost, water uptake, and soil salinity.

Plant stress brought about by frost or cold temperatures results in photooxidative damage to chloroplasts. This is brought about as a result of high light energy in excess of the capacity of chloroplasts to use it for CO₂ fixation at low temperature. This excess energy forms reactive oxygen species (ROS) which impair the photosynthetic processes and damage cells.

A major function of K in plants is the role of osmotic pressure in cells through the maintenance of a high concentration of K in the cell sap. Cold temperatures can result in the formation of ice crystals in plants, which protect themselves against this process by storing sugar and potassium within their cells. Both these substances act to lower the cells freezing point, maintaining cell functionality.

Additionally, the activities of numerous enzymes which might play a part in frost resistance are also dependent on adequate K levels.

There is evidence that plants exposed to stress benefit from more than the usual amount of potassium. For example, large applications have reduced the extent of cold damage in oilseed rape (Table 1).

Table 1. Effect of potassium supply on cold damage in oilseed rape (Australian Soil Fertility Manual)
K2O applied kg/ha	Plants with cold damage %
0	62
75	35
225	19
450	8

The alleviating effect of K is also demonstrated in Table 2 from results of a field experiment on potato grown on sandy soils of varying K levels.

Table 2. Effect of increasing K supply on frost damage (%) and K content of leaves (mg g−1 DW) and tuber yield (t ha−1) of potato on sites with different soil K status (Grewal and Singh, 1980)
K status of the site		K fertilisation rate (kg ha−1)
		0	42	84
low	Frost damagea	65	26	12
	K content	1.64	1.96	2.85
	Tuber yield	18.0	22.9	29.6
medium	Frost damage	52	30	4
	K content	2.28	2.80	2.80
	Tuber yield	19.8	26.0	26.3
high	Frost damage	12	12	0
	K content	2.61	2.79	2.82
	Tuber yield	20.7	22.4	23.4
a Percentage of foliage damaged by frost in the field

In this experiment, potassium fertilisation increased frost resistance on all three soils and particularly so on the soil of lowest K status. The effect of increasing potash fertiliser application in mitigating frost damage on the soil of medium K status without effecting tuber yield indicates the requirement of higher K supply to improve frost resistance at low temperatures.

It is not just potassium that can improve a crops tolerance to cold temperatures, various observations have been made relating to the impact of calcium and phosphorus, as well as some micronutrients. Potassium should not therefore be considered in isolation for this purpose.

The risk of frost may have subsided for the time being as temperatures have risen dramatically, but late frosts arguably are a greater cause for concern, when plants are further forward, containing more water, and the potential for potassium deficiency is greater.