Ensuring an adequate supply of potassium can improve the ability of crops and pastures to tolerate stress from soil moisture, temperature, disease and pests.
The positive effects of potassium include improved:
Water Use Efficiency
Where crop yields are limited by soil moisture, correcting potassium deficiencies can ensure the most efficient use of available water. Water use efficiency (WUE) is defined as the amount of plant yield produced per unit of water used. Water can be lost from a field by transpiration through the plant, and by evaporation (collectively evapotranspiration).
Adequate potassium fertilisation can improve WUE by increasing yields and decreasing water lost by evapotranspiration. The positive effect of potassium on photosynthesis means that the plant has more photosynthetic substrate available to produce vegetation and grain. In addition, the canopy of a rapidly growing crop will close earlier than that of a nutrient deficient crop, and will therefore reduce evaporative losses from the soil surface. Improved control of stomata because of adequate potassium supply can also improve the efficient use of water by speeding up the opening and closing response to environmental conditions such as hot dry weather.
Disease and Insect Resistance
Potassium is known to affect plant susceptibility to diseases and pests by influencing tissue cell structures and biochemical processes. Physical resistance to pests is improved because adequate potassium supply ensures complete closure of plant stomata and increases the lignification of vascular tissue.
Potassium deficient plants have low total carbohydrate content, but have a higher concentration of soluble sugars which provides a suitable substrate for the growth of many pathogens.
Where nitrogen is well supplied, cell walls of plants can be thinner because of rapid growth rates, exposing plants to attack from pests or diseases. So it is important to ensure that nitrogen application is balanced with adequate potassium.
The positive effect of potassium on cell and tissue structure means that crops which are well supplied with potassium are more resistant to lodging than crops which are potassium deficient.
Application of potassium fertiliser to a North American sorghum crop in a soil with very low potassium supplies resulted in a dramatic decrease in lodging. Click on the graph below for more details.
Overseas research has suggested that adequate potassium nutrition can reduce frost damage in tree fruits, potatoes and ornamentals. But attempts by Australian researchers to measure the effect of potassium application on frost damage in wheat have so far been inconclusive.