Potassium chloride (commonly referred to as Muriate of Potash or MOP) is the most common
Its nutrient composition is approximately:
Potassium: 50%
Chloride: 46%
MOP has a high nutrient concentration and is therefore relatively price competitive with other
forms of potassium. The chloride content of MOP can also be beneficial where soil chloride is low. Recent research has shown that chloride improves yield by increasing disease resistance in crops. In circumstances where soil or irrigation water chloride levels are very high, the addition of extra chloride with MOP can cause toxicity. However, this is unlikely to be a problem, except in very dry environments, since chloride is readily removed from the soil by leaching.
Why muriate of potash could be killing your soil
Muriate of potash is a naturally occurring substance that is usually mined. A chemically formulated version of this is used widely now as a potassium fertiliser. The problem with using Muriate of Potash as a fertiliser is that the potassium ion in this type of potash is also linked to a chlorine ion. The chemical formula for muriate of potash is KCl (Potassium Chloride).
The problem with Chlorine
Potassium Chloride is highly soluble and the high salt index may disrupt osmotic gradients in the rhizospere and thereby harm bacteria and fungi even at low concentrations. It is the presence of chloride in muriate of potash that causes concern for farmers. Free chloride in the soil solution may reduce activity of fungi, bacteria, algae and other soil microorganisms that are vital for healthy soil function.
Even a tiny amount can be harmful
Even a tiny amount can be harmful
Following an application of 100Kg/Ha of muriate of potash, enough chloride is present to create around 20 parts per million (ppm) of chloride in the soil solution to a depth of 75mm.
Luckily, chloride is highly soluble and therefore will not stay long in the soil so the effect of each fertilizer application is short lived. However muriate of potash will still disrupt the activity of many of the beneficial soil microbes every time it is applied. The soil can recover from this as the microorganisms gradually re-establish their populations once the chloride levels drop off, however, since plants rely on the microorganisms to feed and protect them it is better to choose another source of potassium when planning your biological fertiliser programme. After all, the less damage we can do to what are sometimes fragile populations of soil microorganisms, the better.
So what should you use instead?
Luckily, chloride is highly soluble and therefore will not stay long in the soil so the effect of each fertilizer application is short lived. However muriate of potash will still disrupt the activity of many of the beneficial soil microbes every time it is applied. The soil can recover from this as the microorganisms gradually re-establish their populations once the chloride levels drop off, however, since plants rely on the microorganisms to feed and protect them it is better to choose another source of potassium when planning your biological fertiliser programme. After all, the less damage we can do to what are sometimes fragile populations of soil microorganisms, the better.
So what should you use instead?
Fortunately, there are many other sources of potassium you can use which are just as effective in addressing potassium imbalances but don’t sterilise your soil. These include:
Potassium Sulphate (K2SO4) (Provides Sulphate sulphur as well as potassium)
Potassium Oxide (K2O)
Potassium Carbonate (K2CO3)
Mono Potassium Phosphate (MKP) (Provides soluble phosphate as well as potassium)
Potassium Sulphate (K2SO4) (Provides Sulphate sulphur as well as potassium)
Potassium Oxide (K2O)
Potassium Carbonate (K2CO3)
Mono Potassium Phosphate (MKP) (Provides soluble phosphate as well as potassium)