Magnesium guide
Magnesium is a secondary nutrient at the centre of every chlorophyll molecule. The crop also needs it to make and use energy and to move...
Read the full guidePotash, magnesium and calcium: the balance that decides leaf colour
How potassium, magnesium and calcium compete at the root, why heavy potash causes magnesium shortage, and when a calcium problem is really magnesium.
Potassium, magnesium and calcium are taken up through the same doors in the root, so too much of one shuts out the others. Heavy potash brings on magnesium shortage, and an imbalance between magnesium and calcium can show symptoms that are treated with the wrong nutrient. A soil test that shows all three together is the way to see the balance.
By Gafar Laiya and the Gujarat Bio Organics team. Updated November 2026.
How the competition works
- Potassium, magnesium and calcium are all positively charged and compete for uptake.
- Heavy potash or ammonium lowers magnesium and calcium uptake.
- Heavy lime or calcium lowers magnesium and potassium uptake.
When the wrong nutrient gets the blame
- A crop can show calcium-type fruit problems when the real limit is magnesium balance or water movement.
- Spraying calcium again and again then does not solve it.
- Testing all three nutrients together shows which one is out of balance.
What to do
- Test exchangeable potassium, magnesium and calcium together.
- Apply potash to the test, not by habit.
- Add magnesium where it is short, especially on heavily potash-fed crops.
- Keep watering steady so calcium can move.
Read more
Doses depend on the crop, soil and product, so this page gives methods, not amounts. Take the dose from your soil test report, the product label or your local agriculture officer or KVK. Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.
Read next
Magnesium deficiency symptoms crop by crop
How magnesium deficiency looks in cotton, grapes, citrus, potato, banana, sugarcane and coconut, and how to tell it from potash and nitrogen shortage.
Read the full guideHow Gujarat Bio Organics can help
Since 2006, lakhs of farmers from Kashmir to Kanyakumari have used Immunity products on almost every crop: from the mango farms around Somnath to the apple orchards of Himachal Pradesh and Kashmir, the tea estates of Assam and Darjeeling, and the banana, coconut and cardamom farms of Tamil Nadu, Karnataka and Kerala. Each Special is one formula made for one crop and its common problems. Tell us your crop, soil test and what you see, and our team will tell you what to check, whether a micronutrient correction is needed, and which Special fits your programme.
- Cotton guide and Immunity Cotton Special
- Citrus guide and Immunity Citrus Special
- Potato guide and Immunity Potato Special
- Banana guide and Immunity Banana Special
- Sugarcane guide and Immunity Sugarcane Special
- Coconut guide and Immunity Coconut Special
Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.
Questions
Should I cut potash if magnesium is short?
Not below what the crop needs. Add magnesium so the two are in balance.
Which test shows the balance?
A soil test that reports exchangeable potassium, magnesium and calcium, and a leaf test if the problem continues.