Potassium for Optimal Water Supply and Water Use Efficiency of Plants
The uptake of water by the plant’s root and the transport of the water to other parts of the plant are significantly determined by potassium (K+). Mainly K+, but also other “osmotically” effective compounds, such as sugar, are necessary for the osmotic process of taking water in. Following the same principle, water is then transported to the xylem. The pressure created by this is called `turgor´.
Potassium Protects Plants Against Desiccation
Due to its osmotic properties, potassium is involved in the opening and closing process of the leaves’ guard cells, and thereby in controlling the vapour loss to the environment. Releasing vapour into the atmosphere helps to keep plants cool. If this evaporation is too strong, with insufficient water entering the roots, the stomata are closed to better protect the plant against desiccation.
Lack of Potassium and Water Stress Will Result in the Following:
- The osmotic effect of the potassium will need to be replaced by organic compounds (sugar). These compounds are then no longer available for plant growth and for storage in the storage organs.
- Opening and closing of the stomata no longer functions. The plant will initially wilt, and if the lack of potassium is prolonged, will drop its older leaves.
In both cases, harvests will be reduced, i.e. depending on the crop there will be fewer grains, smaller cobs, smaller roots, etc. Potassium deficiency will impede the plant’s ability to fully use the water available in the soil or supplied by irrigation for yield formation. Adequate potassium fertilisation can improve water supply to the plant and increase water use efficiency (dry mass yield per water unit [g/l]).
Higher Yields with Potassium Fertiliser
A water supply of 60% of the maximum water storage capacity to oilseed rape showed the expected yield raise after potassium fertilisation. A water supply of only 30% of the maximum water storage capacity showed even more pronounced effects of potassium fertilisation on yield.
Potassium Support the Water Storage Capacity of the Soil
Even beyond the direct effect of potassium on the plant, there is evidence that a sufficient supply of potassium raises the soil’s water storage capacity, i.e. to keep more water within the top soil, against the effect of gravity. This effect of potassium on the soil is the topic of ongoing scientific research.