potassium deficiency

Plants are similar to us humans and animals in that when under stress from poor nutrition, our bodies suffer in growth, development, and general health. Animals show these disorders in the form of weak bones, skin discolouration, and poor weight. Plants show nutritional defects in their vigour, strength of the stems, colour of the leaves and poor yields.

Whenever plants undergo any type of stress from environmental conditions to lack or excess of nutrients, they will express signs of disorders. Pest and diseases also cause stress and disorders within the plant.

Symptoms of disorders within the plant may be expressed as leaf yellowing (chlorosis), browning (necrosis), burning (white colouration due to loss of chlorophyll in leaves), deformation of leaves and growing tips, and stunting of overall growth. The first thing to observe with a nutrient disorder is the location of the affected tissue.

 

 

 

 

 

 

Leaves will, in general, show the symptoms first. If it is a root problem due to disease or lack of oxygen, examination of the roots will reveal that they are not turgid and white, but limy and brown. The plant will wilt during high light periods as the water loss by transpiration is greater than the roots ability to take up sufficient water.

The location of symptoms on the plant is the first clue as to the cause of the disorder. Focusing on leaf symptoms, if the lower leaves are expressing yellowing, browning, or spots first, then the group of nutrients responsible for the disorder would be those of “mobile” elements. Mobile elements can be retranslated within the plant from the lower order tissue to the younger tissues in the top of the plant. These elements include N, P, K, Mg, Zn and Mo. Initial symptoms will be a yellowing (chlorosis) followed by browning or drying (necrosis) of leaf tissue. If the symptoms appear in the young leaves at the tip of the plant, this disorder is a result of a lack of “immobile” elements that cannot move from the older plant parts to the growing tip. These immobile elements are Ca, B, Cu, Mn, S and Fe. To determine which of these is the cause of the disorder there are some visual “keys” listed below allowing you to make a number of alternative choices. Each selection narrows the possible causes in the final step, there is a single element identified.

• It is critical to recognize any symptoms occurring at an early stage of the plants, expression of these stress clues because as the disorder goes on without correction, the symptoms expand progressing from simple yellowing spots to complete yellowing and necrosis. At that stage, it is very difficult to know the first form of symptoms as they spread throughout the plant giving it an overall chlorosis, necrosis, and deformation of tissues. In addition, as the stress becomes more severe, it will be difficult, taking a lot of time to correct it once identified. The loss of the plant’s health may become permanent or event result in its death. Yields will be greatly reduced as the stress is not corrected. The stress may begin as a cause from a single element and then as it progresses, another element uptake is slowed or blocked and the plant suffers from multiple disorders. A very useful procedure when a symptom first appears is to immediately change the nutrient solution. That is, make up a new batch. At the same time, to determine the exact cause send a nutrient or tissue sample to a laboratory for analysis. Similar to soil analysis, the laboratory will give you guidelines as to what the normal leaves of each nutrient should be in the solution or in the plant and direct you to make adjustments in the nutrient solution formulation.

Mobile Elements Deficiencies: -   

Nitrogen: -

• Lower leaves become yellowish green and growth is stunted

Remedies: -

• Add calcium nitrate or potassium nitrate to the nutrient solution.

Phosphorous: -

• Stunted growth of the plant, a purple colour of the undersides of the leaves is very distinct and leaves fall off prematurely.

Remedies: -

• Add monopotassium phosphate to the nutrient solution.

Potassium: -

• The leaflets on older leaves of tomatoes become scorched, curled margins, chlorosis between veins in the leaf tissue with small dry spots. Plant growth is restricted and stunted. Tomato fruits become blotchy and unevenly ripen.

Remedies: -

• Apply a foliar spray of 2% potassium sulfate and add potassium sulfate to the nutrient solution.

 Magnesium: -

• The older leaves have interveinal (between veins) chlorosis from the leaf margins inward, necrotic spots appear.

Remedies: -

• Apply a foliar spray of 2% magnesium sulfate, add magnesium sulfate to the nutrient solution.

Note: - When applying foliar sprays, if in a greenhouse, avoid doing during high sunlight conditions as that can cause burning of the leaves. Apply in the early morning while the sun and temperatures are low.

 Zinc: -

• Older and terminal leaves are abnormally small. The plant may get a “bushy” appearance due to the slowing of growth at the top.

Remedies: -

• Use a foliar spray with1%-0.5% solution of zinc sulfate. Add zinc sulfate to the nutrient solution.

 Immobile elements: -

• First, the symptoms appear on the younger leaves at the top of the plant.

 Calcium: -

• The upper leaves show marginal yellowing progressing to leaf tips, margins wither, and petioles curl and die back. The growing point stops growing and the smaller leaves turn purple-brown colour on the margins, the leaflets remain tiny and deformed. Fruit of tomatoes shows blossom-end rot.

Remedies: -

• Apply a foliar spray of 1.0% calcium nitrate solution. Add calcium nitrate to the nutrient solution.

 Sulfur: -

• Upper leaves become stiff and curl down, leaves turn yellow. The stems, veins and petioles turn purple and plant growth is restricted.

Remedies: -

• Add potassium sulfate or other sulfate compounds to the nutrient solution. A sulfur deficiency is usually rare because it is added to the nutrient solution by use of potassium, magnesium, and other sulfate salts.

 Iron: -

• The terminal leaves start turning yellow at the margins and progress through the entire leaf leading eventually to necrosis. Initially, the smallest veins remain green giving a reticulate pattern. Flowers abort and fall off, growth is stunted and spindly in appearance.

Remedies: -

• Apply a foliar spray with 0.02%-0.05% solution of iron chelates every 3-4 days. Add iron chelate to the nutrient solution.

 Boron: -

• The growing point withers and dies. Upper leaves curl inward and are deformed having interveinal mottling (blotchy pattern of yellowing). The upper smaller leaves become very brittle and break easily.

Remedies: - 

• Apply a foliar spray of 0.1%-0.25% borax solution. Add borax or boric acid to the nutrient solution.

 Copper: -

• Young leaves remain small, margins turn into a tube toward the midribs in tomatoes, petioles bend downward, and growth is stunned to get a “bushy” appearance of the plant at the top.

 Remedies: -

• Use a foliar spray of 0.1% - 0.2% solution of copper sulfate. Add copper sulfate to the nutrient solution.

Note: - whenever applying a foliar nutrient spray, apply it first to a few plants and wait to apply it to all plants for about a day to be sure that no burn occurs from the spray.

Manganese: -

• Middle and younger leaves turn pale and develop a characteristic checkered pattern of green veins with yellowish interveinal areas. Later small necrotic spots form in the pale areas. Shoots will become stunted.

Remedies: -

• Apply a foliar spray of 0.1% manganese sulfate solution. Add manganese sulfate to the nutrient solution.

Molybdenum: -

• All leaves show a pale green to yellowish interveinal mottling. Usually progresses from the older to the younger leaves.

Remedies: - 

• Apply a foliar spray of 0.07%-0.1% solution of ammonium or sodium molybdate. Add ammonium or sodium molybdate to the nutrient solution.

Potassium is a paramount macro-element for overall survival of living things. It is an abundant mineral macronutrient present in both plant and animals tissues. It is necessary for the proper functioning of all living cells. Potassium is relatively abundant in the earth's crust making up to 2.1% by weight. Potassium is mined in the form of potash (KOH), sylvite (KCl), Carnallite and Langbeinite. It is not found in free nature.

Importance of potassium to plants

Potassium is an indispensable constituent for the correct development of plants. It is important in photosynthesis, in the regulation of plants responses to light through opening and closing of stomata. Potassium is also important in the biochemical reactions in plants. Basically, potassium (K) is responsible for many other vital processes such as water and nutrient transportation, protein, and starch synthesis.

Potassium Uptake

Bio-availability and uptake of K by plants from the soil vary with a number of different factors. The rate of respiration by plants is largely the determining factor for proper uptake and transport of potassium by plants. Its uptake is dependent on sufficient energy (ATP). Potassium plays a vital role in the translocation of essential nutrients, water, and other substances from the roots through the stem to the leaves. It is also made available through fertilizers in the form of K2O. Plant tissues analyze the form of these fertilizers and convert it into a more bio-available form. It is absorbed in the form of ions- K+.

Functions of Potassium in plants

Potassium (K) essentially plays a major role in plant physiological processes. Therefore, it is required in large amounts for proper growth and reproduction in plants. It is considered vital after nitrogen as far as nutrients needed by plants are concerned. It is also termed "the quality nutrient" for its contributing factor in a number of biological and chemical processes in plants. Here is why Potassium is important in plants:

• Potassium regulates the opening and closing of stomata thus regulating the uptake of CO2 thus enhancing photosynthesis.
• It triggers activation of important biochemical enzymes for the generation of Adenosine Triphosphate (ATP). ATP provides energy for other chemical and physiological processes such as excretion of waste materials in plants.
• It plays a role in osmoregulation of water and other salts in plant tissues and cells.
• Potassium also facilitates protein and starch synthesis in plants.
• It activates enzymes responsible for specific functions.

Potassium deficiency in plants

Regardless of its availability from soils, potassium deficiency may occur and might start from the lower leaves and progress towards other vital parts of the plants. Deficiency might cause abnormalities in plants affecting reproduction and growth. Severity depends on with the type of plant and soil. Some of the potassium deficiency symptoms may include:

• Chlorosis: May cause yellowing of leaves, the margin of the leaves may fall off, and also lead to shedding and defoliation of the leaves.
• Stunted growth: Potassium being an important growth catalyst, its deficiency or insufficient might lead to slow growth or poor developed roots and stems.
• Poor resistance to ecological changes: Reduced availability of potassium will directly result in less fluid circulation and translocation of nutrients in plants. This will directly make plants susceptible to temperature changes.

Importance of potassium in agriculture

Potassium is important in agriculture and soil gardening. It is used as a constituent in artificial fertilizers. Potassium fertilizers have been seen to increase crop yields, enhance production of grains rich in starch and protein content of plants. Additionally, potassium fertilizers may help improve plants immunity to weather changes, diseases, and nematodes.

Potassium is majorly used in hydroponics to improve root growth and enhance drought tolerance. It also enhances the building of cellulose and thus reduces lodging.