Most farmers in India know potash as the red granules of MOP, muriate of potash. Over the last few years PDM, potash derived from molasses, has become a common second option at the dealer counter. They are not the same product, and the cheaper bag is not always the cheaper choice.
What each one is
MOP is potassium chloride, mined and almost entirely imported into India. It carries about 60% K2O.
PDM is recovered from the spent wash left after sugar mills distil molasses. CNF PDM carries a minimum of 14.5% water-soluble K2O, along with organic matter and small amounts of other nutrients from the original cane.
Compare on potash, not on bags
A 50 kg bag of MOP holds about 30 kg of K2O. A 50 kg bag of PDM 14.5% holds 7.25 kg. So you need roughly four bags of PDM to put the same potash on the field as one bag of MOP.
To compare price fairly, work out the cost of one kg of potash:
- MOP: bag price ÷ 30
- PDM: bag price ÷ 7.25
Then add what each bag brings beyond potash. With PDM that is organic matter and the absence of chloride. With MOP it is fewer bags to carry and spread.
When chloride matters
MOP is about 47% chloride. For many field crops that is not a problem at normal doses. For some crops it is:
- Tobacco: chloride spoils leaf burning quality.
- Grapes, potato and many fruits and vegetables: sensitive to chloride, especially at high doses.
- Saline soils or salty borewell water: extra chloride adds to the salt load.
On these fields a chloride-free potash such as PDM, or sulphate of potash through drip, is the safer pick.
Timing for flowering
Whichever source you use, potash does most of its work from flowering onwards, moving sugars into the fruit or grain and helping the crop handle heat. Split the dose: part as basal, part as a top dressing just before flowering. In sugarcane, the second split goes in at earthing up.
The short answer
If your crop is chloride-sensitive, your soil is low in organic matter, or your water is salty, PDM earns its place. If you only need the cheapest potash on a tolerant crop, compare the cost per kg of K2O first. Ask your dealer for both prices, or ask us and we will work it out with you.
