>ROLE OF POTASSIUM IN PLANTS

Potassium is an essential plant nutrient and is required in large amounts for proper growth and reproduction of plants. Potassium is considered second only to nitrogen, when it comes to nutrients needed by plants, and is commonly considered as the “quality nutrient.”

Potassium (K) is the third of the three primary nutrients required by plants along with nitrogen (N) and phosphorus (P). When you read the label on a bag of fertilizer (e.g.: 20-10-20), the third number indicates the percentage of potassium by weight in the fertilizer. Technically, this number refers to K2O, which is 83% elemental K by weight. Water-soluble fertilizers are typically formulated using potassium nitrate or potassium sulfate as the source of potassium. In cases where sulfate is lacking in a fertilization program, potassium sulfate is a useful material. However, potassium chloride could also be used, but should be avoided since the added chloride is not needed by plants and contributes unwanted salts.

It affects the plant shape, size, color, taste and other measurements attributed to healthy produce.
Plants absorb potassium in its ionic form, K+.

Function/ROLES OF POTASSIUM IN PLANTS:

Potassium has many different roles in plants:
• In Photosynthesis, potassium regulates the opening and closing of stomata, and therefore regulates CO2 uptake.
• Potassium triggers activation of enzymes and is essential for production of Adenosine Triphosphate (ATP). ATP is an important energy source for many chemical processes taking place in plant issues.
• Potassium plays a major role in the regulation of water in plants (osmo-regulation). Both uptake of water through plant roots and its loss through the stomata are affected by potassium.
• Known to improve drought resistance.
• Protein and starch synthesis in plants require potassium as well. Potassium is essential at almost every step of the protein synthesis. In starch synthesis, the enzyme responsible for the process is activated by potassium.
• Unlike nitrogen and phosphorus, potassium is not used in the structural synthesis of bio-chemically important molecules. Potassium is found within the plant cell solution and is used for maintaining the turgor pressure of the cell (meaning it keeps the plant from wilting). In addition, potassium plays a role in the proper functioning of stomata (cells located on the bottom of the leaf that open and close to allow water vapor and waste gases to escape) and acts as an enzyme activator.
• Activation of enzymes: potassium has an important role in the activation of many growth related enzymes in plants.
• The main role of potassium is to provide the ionic environment for metabolic processes in the cytosol, and as such functions as a regulator of various processes including growth regulation.[2] Plants require potassium ions (K+) for protein synthesis and for the opening and closing of stomata, which is regulated by proton pumps to make surrounding guard cells either turgid or flaccid. A deficiency of potassium ions can impair a plant's ability to maintain these processes. Potassium also functions in other physiological processes such as photosynthesis, protein synthesis, activation of some enzymes, phloem solute transport of photoassimilates into source organs, and maintenance of cation:anion balance in the cytosol and vacuole.

POTASSSIUM DEFICIENCY IN PLANTS:

In soilless growing media, potassium availability is not significantly influenced by pH. Potassium deficiency symptoms are most likely to appear when insufficient potassium is provided by fertigation. There are also situations where an induced potassium deficiency arises if calcium, magnesium or sodium levels are too high, but it is rare if a crop is fed with normal potassium rates.

Potassium deficiency might cause abnormalities in plants, usually the symptoms are growth related.

Potassium defficiency symptoms:
• Typical symptoms of potassium deficiency in plants include brown scorching and curling of leaf tips as well as chlorosis (yellowing) between leaf veins. Purple spots may also appear on the leaf undersides. Plant growth, root development, and seed and fruit development are usually reduced in potassium-deficient plants. Often, potassium deficiency symptoms first appear on older (lower) leaves because potassium is a mobile nutrient, meaning that a plant can allocate potassium to younger leaves when it is K deficient.[3] Deficient plants may be more prone to frost damage and disease, and their symptoms can often be confused with wind scorch or drought. The deficiency is most common in several important fruit and vegetable crops; notably potatoes, brassicas, tomatoes, apples, currants, gooseberries, and raspberries.
• Cholrosis: scorching of plant leaves, with yellowing of the margins of the leaf. This is one of the first symptoms of Potassium deficiency. Symptoms appear on middle and lower leaves.
• Slow or Stunted growth: as potassium is an important growth catalyst in plants, potassium deficient plants will have slower or stunted growth.
• Poor resistance to temperature changes and to drought: Poor potassium uptake will result in less water circulation in the plant. This will make the plant more susceptible to drought and temperature changes.
• Defoliation: left unattended, potassium deficiency in plants results in plants losing their leaves sooner than they should. This process might become even faster if the plant is exposed to drought or high temperatures. Leaves turn yellow, then brown and eventually fall off one by one.

Other symptoms of Potassium deficiency:
• Poor resistance to pests
• Weak and unhealthy roots
• Uneven ripening of fruits
Leaf tissue analysis shows that potassium levels are often close to those of nitrogen at around 3 to 5% on a dry weight basis. Plants that are potassium deficient typically show symptoms such as chlorosis followed by necrosis at the tips and along the margins of leaves. Since potassium is mobile within the plant, deficiency symptoms appear on older leaves.

Potassium deficiency in Poinsettia:

“Potassium deficiency seen in poinsettias as necrotic leaf edges.”

In potatoes:

Tuber size is much reduced and crop yield is low. The leaves of the plant appear dull and are often blue-green in color with intervenal chlorosis. Leaves will also develop small, dark brown spots on the undersides and a bronzed appearance on the upper surfaces.

In brassicas:

Leaves are blue-green in color and may have a low degree of intervenal chlorosis. Scorching along the outside edges of leaves is common, and leaves are often tough in texture due to slow growth.

In tomatoes:

The stems are woody and growth is slow. Leaves are blue-green in color, and the intervenal area often fades to a pale gray color. Leaves may also have a bronzed appearance and yellow and orange patches may develop on some of the leaflets. Fruits often ripen unevenly and sometimes have green patches near the stalks.

In apples:

Leaves are scorched around the edges, and intervenal chlorosis is common. Apple fruits often have a slightly acidic or woody taste.

In gooseberries, currants, and raspberries:

Dieback of shoots and branches is common and although the plant may produce many blossom buds in the early stages of deficiency, fruit yields turn out low and the fruits are of poor quality.

Potassium deficiency and plant disease:

For many species, potassium-deficient plants are more susceptible to frost damage and certain diseases than plants with adequate potassium levels. Increased disease resistance associated with adequate potassium levels indicates that potassium has roles in providing disease resistance, and increasing the potassium levels of deficient plants have been shown to decrease the intensity of many diseases. However, increasing potassium concentration above the optimal level does not provide greater disease resistance. In agriculture, some cultivars are more efficient at K uptake due to genetic variations, and often these plants have increased disease resistance.[1] The mechanisms involved with increased host resistance and potassium include a decreased cell permeability and decreased susceptibility to tissue penetration. Silica, which is accumulated in greater quantities when adequate potassium is present, is incorporated into cell walls, strengthening the epidermal layer which functions as a physical barrier to pathogens. Potassium has also been implicated to have a role in the proper thickening of cell walls.

Proper fertilizer management can avoid potassium deficiencies and damage to crops.

Toxicity:

Potassium toxicity does not exist per se. However, excessive levels of potassium can cause antagonisms that lead to deficiencies in other nutrients such as magnesium and calcium. If this occurs, it is best to test the growing medium and plant tissue for nutrient content and adjust the fertilization program or application rate. Prevention and cure:The most widely used potassium fertilizer is potassium chloride (muriate of potash). Other inorganic potassium fertilizers include potassium nitrate, potassium sulfate, and monopotassium phosphate. Potassium-rich treatments suitable for organic farming include feeding with home-made comfrey liquid, adding seaweed meal, composted bracken, and compost rich in decayed banana peels. Wood ash also has high potassium content. Adequate moisture is necessary for effective potassium uptake; low soil water reduces K uptake by plant roots. Liming acidic soils can increase potassium retention in some soils by reducing leaching;[1] practices that increase soil organic matter can also increase potassium retention.