A practical guide to potassium chloride, why fertilizer analysis is quoted as K2O, when chloride sensitivity rules it out, and how it is supplied, from a US-based distributor.
Potassium chloride (KCl, CAS 7447-40-7), known in agriculture as muriate of potash or MOP, is the primary potassium fertilizer and the cheapest source of potassium by a wide margin. Fertilizer grade typically analyzes 60–62% K2O equivalent. It suits most field crops but not chloride-sensitive ones. Stratus Chemical supplies agricultural and technical grades in bags, supersacks, and bulk across the United States.
| Property | Value |
|---|---|
| Chemical name | Potassium chloride |
| Synonyms | Muriate of potash, MOP, potassium muriate, sylvite |
| CAS number | 7447-40-7 |
| Molecular formula | KCl |
| Molecular weight | 74.55 g/mol |
| EC / EINECS | 231-211-8 |
| Appearance | White solid crystal |
| Grades supplied | Agricultural (MOP), technical / industrial |
| Packaging | Bags, supersacks, bulk |
| Documentation | COA & SDS provided on request |
The figures below are representative of fertilizer grade potassium chloride. They are indicative rather than guaranteed: specifications vary by source and by lot, and the certificate of analysis for your material governs.
| Parameter | Typical | Guaranteed |
|---|---|---|
| Potassium oxide equivalent (K2O) | 62.2% | 62.0% min |
| Potassium chloride (KCl) | 98.4% | 98.2% min |
| Potassium (K+) | 51.6% | — |
| Sodium chloride (NaCl) | 1.44% | — |
| Sodium (Na+) | 0.6% | — |
| Calcium (Ca2+) | 0.015% | — |
| Magnesium (Mg2+) | 0.004% | — |
| Sulfate (SO42−) | 0.04% | — |
| Water insolubles | 0.02% | — |
| Moisture (H2O) | 0.08% | 0.5% max |
| Bulk density | 1,120 – 1,150 kg/m³ | — |
| Angle of repose | 24 – 28 degrees | — |
| Size guide number (SGN) | 51 – 64 | — |
| Packing options | 50 lb bags, big bags / totes, bulk | |
Potassium chloride is a simple ionic salt, mined from ancient evaporite deposits as the mineral sylvite or recovered from brines. It is the dominant potassium fertilizer worldwide, accounting for the large majority of potash consumption, and its position rests on economics: no other potassium source comes close on cost per unit of nutrient.
Potassium is one of the three primary plant nutrients alongside nitrogen and phosphorus. It regulates water movement and stomatal function, strengthens stalks and cell walls, improves disease resistance, and drives the quality attributes buyers pay for, including grain fill, fruit size, and sugar content. Deficiency shows first as scorching along the margins of older leaves.
This is the single most common source of confusion in potash specification, and it is worth being clear about.
Fertilizer labelling convention expresses potassium as potassium oxide equivalent, written K2O, rather than as elemental potassium. This is a historical carryover from oxide-based analysis, and no potassium oxide is actually present in the product. A material quoted at 62% K2O contains roughly 51% actual potassium; the conversion factor is about 0.83.
The practical consequence is that a product quoted on an elemental basis will look weaker than the identical material quoted as K2O. Before comparing two quotes, check which basis each is using. The specification table above lists both, which is why the K2O figure of 62.2% and the potassium figure of 51.6% describe the same material.
The primary use. Granular potassium chloride is spread directly or blended with urea, ammonium sulfate, phosphates, and micronutrients into custom NPK blends. Particle size matters here more than most buyers expect: if the size guide number of the potash does not match the other blend components, the blend segregates in the spreader and the field receives an uneven application.
Soluble grades dissolve for delivery through irrigation. Water insolubles and the sodium content are the parameters to watch, since insoluble residue blocks emitters and drip lines.
Potassium chloride is used as a potassium supplement in livestock and poultry diets, particularly in high-production dairy rations and in heat-stress situations where potassium requirements rise.
Technical grades go into oilfield drilling fluids, where potassium chloride stabilizes reactive shale formations, into water softener regeneration as a sodium-free alternative, and into the manufacture of potassium hydroxide, potassium carbonate, and other potassium chemicals.
| Potassium source | How it behaves | Trade-off |
|---|---|---|
| Potassium chloride (MOP) | Approximately 60–62% K2O, fully soluble, lowest cost per unit K | Supplies chloride, which some crops and saline soils cannot tolerate |
| Potassium sulfate (SOP) | Approximately 50% K2O plus around 18% sulfur, chloride-free | Suits chloride-sensitive crops and adds sulfur, but substantially more expensive |
| Potassium nitrate | Supplies potassium and nitrate nitrogen, highly soluble, low salt index | Excellent for fertigation and foliar use, but the highest cost per unit potassium |
| Potassium magnesium sulfate | Supplies potassium, magnesium, and sulfur together, chloride-free | Useful where magnesium is also limiting, but low potassium analysis means high freight |
How to choose: chloride tolerance decides it first. Corn, soybeans, small grains, and most forages handle chloride without difficulty, and for those crops potassium chloride is the economically obvious answer. Tobacco, potatoes, grapes, citrus, avocados, and many vegetables are chloride-sensitive, and on those the sulfate is worth its premium. The second question is soil salinity: on already-saline ground, adding a high-salt-index material can do more harm than the potassium does good. Where the potassium goes through an irrigation system, solubility and insolubles matter more than headline analysis.
Store potassium chloride dry in closed original packaging, off damp floors. It is mildly hygroscopic, and caking is the routine practical complaint: material that has picked up moisture sets in the bag and will not meter or spread evenly afterward.
Potassium chloride solutions are corrosive to mild steel over time, so specify appropriate materials for dissolving tanks, pumps, and lines rather than assuming a benign salt is benign to equipment.
The material is not flammable and presents a low acute hazard, but dust control still applies during bulk handling. Follow the Safety Data Sheet for the specific grade.
Potassium chloride is used chiefly as a potassium fertilizer, supplying the potassium crops need for water regulation, disease resistance, and grain and fruit quality. It is applied directly, blended into dry NPK fertilizers, and dissolved for fertigation. Industrial and technical grades are used in drilling fluids, water softening regeneration, chemical manufacture, and as a raw material for other potassium compounds. Stratus Chemical supplies agricultural and technical grades across the United States.
The CAS number for potassium chloride is 7447-40-7. Its molecular formula is KCl and its molecular weight is 74.55 g/mol. Its EC number is 231-211-8. It is also known as muriate of potash, MOP, potassium muriate, and in its mineral form as sylvite.
They are the same compound. Muriate of potash, usually shortened to MOP, is the fertilizer trade name for potassium chloride; muriate is an archaic term for chloride. The name persists in agricultural markets while potassium chloride is used in chemical and industrial contexts. If a specification calls for MOP and another calls for potassium chloride, they are asking for the same material, though the grade and particle size may differ.
Fertilizer grade potassium chloride typically analyzes around 60 to 62% as K2O equivalent, which corresponds to roughly 50 to 52% actual potassium. Fertilizer labelling convention expresses potassium as K2O rather than elemental K, so the two figures describe the same material and the difference is a units convention, not a quality difference. Always read which basis a specification is using before comparing products.
Potassium chloride is substantially cheaper per unit of potassium and is the right choice for most field crops. Potassium sulfate suits chloride-sensitive crops such as tobacco, potatoes, grapes, and many fruits and vegetables, and it supplies sulfur as well, but it costs considerably more. The deciding questions are whether the crop tolerates chloride and whether the soil already carries a salt load.
Store potassium chloride dry in closed original packaging, off damp floors, and away from prolonged humidity. It is mildly hygroscopic, and the usual practical problem is caking rather than degradation: material that has taken on moisture sets in the bag and becomes hard to spread or blend evenly. Solutions are corrosive to mild steel over time, so use appropriate materials in dissolving and handling equipment.
Stratus Chemical supplies potassium chloride in bags, supersacks, and bulk, in agricultural and technical grades, with a certificate of analysis provided for each shipment. Tell us the grade, particle size, and volume and we will confirm pricing and availability within one business day.
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