After reading this article you will learn about the importance of potassium in the growth of plants.
Next to nitrogen, potassium is the mineral nutrient required in the largest amount by plants. The potassium requirement for optimum plant growth is in the range of 2-5 per cent of the vegetative parts fleshy fruits and tubers of plants (oven dry basis).
Now-a-days, due to intensive cropping systems as well as use of modem agro-techniques the higher rate of application of potassic fertilizers are employed. In order to maintain the fertility level of a soil, the amount of K+ taken up by plants and lost by leaching should at least be balanced by potassium fertilization. However, in highly developed agricultural systems, reserve potassium in soils is being depleted.
In soils having poor potassium availability, its uptake by crops from soil is also low and consequently poor yields are obtained. Under such conditions fertilizer recommendations based on an average total potassium uptake for a particular crop species will not meet the demands of crop nor enhance the soils fertility status.
On the contrary, in soils having high available K, the fertilizer (K) application based on crop K uptake can result in a higher potassium uptake than is needed for maximum yield and hence wastage of potassic fertilizers. The levels of available K in the soil which are considered optimum cannot be stated in general as it depends on plant species as well as climate and soil conditions.
In natrophilic plant species, the requirement for K can be much lower than that of natrophobic plants. When K is deficient, growth is retarded and net re-translocation of K+ is enhanced from older leaves and stems. Under acute K deficiency, the organs like leaves and stems become chlorotic and necrotic depending upon the intensity of light.
In order to assess potassium requirements of crops it is important to consider the total duration. Crops having some total uptake may have different K requirement (uptake/unit time). A requirement also varies depending on the stage of crop growth, the highest uptake rate usually occurs in the vegetative stage.
In cereal crops, potassium is particularly needed during vegetative growth and therefore, the potassium application during the reproductive stage seldomly affects grain yields.
Plants supplied with insufficient amount of potassium are usually more susceptible to frost injury which, at cellular level, is related to water deficiency. Besides, the changes in enzyme activity and organic compounds occurring due to K deficiency are responsible for increased susceptibility to fungal attack.
Such changes in composition of crops especially in fleshy fruits and tubers also affect the nutritional and technological (processing) quality of harvested products.
Type and extent of root systems of crops also affect the potassium uptake. Potassium uptake is considerably higher by cereals especially grasses than that of legumes. Root morphology i.e. length of root, number of root hairs etc., and potassium uptake potential (Reabsorbing power) of a crop species play important factors influencing competition between plant species for potassium.
The response to potassium uptake by different crops depends to a considerable extent on the level of nitrogen nutrition. It has been observed that crops supplied with nitrogen, the yield increase is more due to application of potassic fertilizers. Besides, the better utilization of applied nitrogen has been found only when potassium is applied sufficiently to the soil.
In moving from an extensive to an intensive cropping system responses to potassium fertilizers are frequently not found at the initial first year of its application. However, this is particularly true in more arid regions where little or no losses of potassium particularly through leaching take place.
The amount of potassium present on the surface soil layers is often sufficient to supply crop requirements during initial few years of intensive cropping. However, as soon as such reserve source of potassium in the surface soil is depleted due to crop removal, responses due to potassic fertilization may be expected.