Potassium chloride - the most common potash fertilizer (muriate of potash)

Potassium fertilizers are commonly used to overcome plant deficiencies.

Potassium deficient lettuce

 Where soils cannot supply the amount of K required by crops, it is necessary to supplement this essential plant nutrient. Potash is a general term used to describe a variety of K-containing fertilizers used in agriculture. Potassium chloride (KCl), the most commonly used source, is also frequently referred to as muriate of potash or MOP (muriate is the old name for any chloride-containing salt). Potassium is always present in minerals as a single-charged cation (K⁺).

Production

Deeply buried potash deposits are found throughout the world. The dominant mineral is sylvite (KCl) mixed with halite (sodium chloride), which forms a mixed mineral called sylvinite. Most K minerals are harvested from ancient marine deposits deep beneath the Earth’s surface.

Mining potassium salts in Belarus

They are then transported to a processing facility where the ore is crushed and the K salts are separated from the sodium salts. The color of KCl can vary from red to white, depending on the source of the sylvinite ore. The reddish tint comes from trace amounts of iron oxide. There are no agronomic differences between the red and white forms of KCI.

Potassium fertilizer comes in several colors, depending on their geological source

Some KCl is produced by injecting hot water deep into the ground to dissolve the soluble sylvinite min­eral and then pumping the brine back to the surface where the water is evaporated. Solar evaporation is used to recover valuable potash salts from brine wa­ter in the Dead Sea and the Great Salt Lake (Utah).

Salt beds at the Dead Sea

                      

                        Chemical Properties

                       Property:                            KCl

                     Fertilizer analysis             0-0-60

                     K content approx              50%

                     Water solubility (20^o C)   344 g/L

                     Solution pH                      approx. 7

Agricultural Use

Potassium chloride is the most widely used K fertilizer due to its relatively low cost and because it includes more K than most other sources...50 to 52% K (60 to 63% K₂O) and 45 to 47% Cl^-.

Over 90% of global potash production is used for plant nutrition. Potassium chloride is often spread onto the soil surface prior to tillage and planting. It may also be applied in a concentrated band near the seed. Since dissolving fertilizer will increase the soluble salt concentration, banded KCl is placed to the side of the seed to avoid damaging the germinating plant.

Potassium fertilizer (KMg-SO4)

Potassium chloride rapidly dissolves in soil water. The K⁺ will be retained on the negatively charged cation exchange sites of clay and organic matter. The Cl^- portion will readily move with the water. An especially pure grade of KCl can be dissolved for fluid fertilizers or applied through irrigation systems.

  

Management Practices

Potassium chloride is primarily used as a source of K nutrition. However, there are regions where plants respond favorably to application of Cl^-. Potassium chlo­ride is usually the preferred material to meet this need. There are no significant impacts on water or air associated with normal application rates of KCl. Elevated salt concentrations surrounding the dissolving fertilizer may be the most impor­tant factor to consider.

 

Red potassium chloride

Non-agricultural Use

Potassium is essential for human and animal health. It must be regularly ingested because the body does not store it. Potassium chloride can be used as a salt substitute for individuals on a restricted salt (sodium chloride) diet. It is used as a deicing agent and has a fertilizing value after the ice melts. It is also used in water softeners to replace calcium in water.

Crop Nutrition Problems Can Become Pest Problems

We are familiar with the concept of preventative medicine, where health problems are avoided by good practices instead of curing sickness after they occur. This same concept applies to damage caused to crops by plant diseases and pests when adequate and balanced nutrition is lacking.

Powdery mildew (photo: Wikipedia)

Each nutrient in plants has unique and specific functions that operate in an intricate balance of physiological reactions. A deficiency of a single nutrient will result in stress that impairs healthy plant growth. Until the symptoms of deficiency stress become visible, the hidden roles of proper nutrition in maintaining plant health are too frequently overlooked. 

Healthy and diseased corn leaves (with low potassium)

New scientific studies are again confirming what farmers have known for many years about the link between plant health and nutrition. Healthy plants can generally withstand stress and attack better than plants that are already in poor condition. For example, recent work with corn has demonstrated the link between an adequate K supply and increased leaf thickness, stronger epidermal cells, and decreased leaf concentrations of sugars and amino acids. All of these factors lower the attractiveness of plants for pests, such a spider mites.

The link between adequate K and soybean aphids has also been recently reconfirmed. Research shows that K-deficient soybeans tend to transport more N-rich amino acids in the phloem, making them a favored target of stem-sucking aphids.

Aphid feeding (photo: Wikipedia)

The link between plant nutrition and disease control generally falls into one of these categories where proper fertilization can:

Reduce pathogen activity: Proper mineral nutrition can slow or inhibit the germination and growth of a variety of plant pathogens in soil and in plant cells.

Modify the soil environment: The selection of a N source can temporarily modify the rhizosphere pH during critical periods between germination and seedling establishment. Likewise, the addition of elemental S is a common practice to acidify the root zone of some crops for disease control.

Increase plant resistance: Healthy plant tissues are less susceptible to infection. Proper nutrition can stimulate the production of physical and chemical defenses to cope with pathogens.

Increase tolerance to disease: Adequate nutrition can help plants compensate for disease damage and to sustain a high level of natural compounds that inhibit pathogen growth within plant tissue.

Rice brown spot is more severe with low potassium

Facilitate disease escape: Plants that are adequately fertilized with boron (B) and zinc (Zn) have been shown to have fewer fungal spores that break dormancy on the roots, compared to deficient plants. A healthy photosynthetic capacity also allows for a quick growth response to a pathogen invasion.


Compensate for disease damage: An adequate supply of plant nutrients is closely linked with vigorous root growth and photosynthetic activity. These healthy plants can better tolerate increased disease burdens than plants stressed by nutrient deficiency.

Nutritional and environmental stresses often trigger greater pest and disease damage to crops. While proper fertilization does not eliminate the risk of pests and diseases, it provides an important degree of protection from many yield-robbing factors.

Effective disease and pest management through proper plant nutrition improves crop quality and contributes to provide a safe, abundant, and nutritious food supply.

This post originally appeared in the series "Plant Nutrition Today" on the IPNI website.

Verticillium fungus growing in cotton roots deficient in potassium

The coffee rust fungal disease is not killing the plant, but is attacking the leaves, causing them to drop off. As a result, the plant has fewer coffee beans and at much inferior quality, which makes the cultivation not profitable.

Foliar nutrition can help coping with the coffee rust outbreak as part of the whole treatment. By spraying the fertilizer directly on the leaves, they absorb the nutrients in the most efficient way, leading to immediate response. Thus, the well-nourished plants and leaves have a much better capability of coping with diseases, including the coffee rust.
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