Calcium deficiency
Usually an uptake failure, not a soil shortage — it starves growing tips and the far end of fruit. Blossom-end rot and groundnut "pops" are its signatures.
- Nutrient type
- Secondary
- Mobility in plant
- Immobile
- Symptoms start on
- Growing tips & fruit ends
- Most at risk
- Acidic, sandy soils; erratic moisture
Overview
Most Indian soils, unless strongly acidic, hold plenty of calcium — so calcium deficiency is usually not about how much is in the soil, but whether the plant can move it to where it is needed. Calcium travels only upward with the water stream (transpiration), and cannot be redistributed once deposited. So it reaches leaves easily but starves the parts water reaches last: the growing tips and the blossom (far) end of rapidly-swelling fruit.
That is why the symptoms are so specific — blossom-end rot, a sunken black patch at the bottom of tomato, chilli and capsicum fruit; tip burn of the inner leaves of cabbage and lettuce; and "pops" in groundnut, empty pods that never fill. Anything that interrupts the water stream — erratic irrigation, humidity swings, root damage, or too much potassium/magnesium competing for uptake — can trigger it even on a calcium-rich soil.
How to spot it
- Blossom-end rot: a water-soaked spot at the bottom (blossom end) of tomato, chilli and capsicum that turns into a sunken leathery black patch.
- Growing tips and the youngest leaves distort, hook and die back; new leaves may stay small with brown scorched edges (tip burn) in cabbage and lettuce.
- In groundnut, "pops" — pods that rattle empty because the kernel never filled, a calcium shortage in the pegging zone.
- Roots are short and brown-tipped; the plant looks otherwise green because mature leaves get enough calcium.
Why it happens
- Erratic or interrupted irrigation — calcium rides the water stream, so a dry spell followed by a flush is a classic trigger for blossom-end rot.
- Strongly acidic soils (low pH) are genuinely low in available calcium; sandy soils hold little.
- Too much potassium, magnesium or ammonium fertiliser competes with calcium at the root and blocks its uptake.
- In groundnut, calcium must be present in the top-soil pegging zone at pod-set; a deficiency there causes pops even if deeper soil has calcium.
Confirm before you spend
- Blossom-end rot is often mistaken for a disease or pest — it is neither; it is a calcium-delivery problem driven by uneven watering. No spray fixes erratic moisture.
- Check whether the soil is genuinely acidic/low in calcium (a soil test) or whether this is an uptake problem on adequate soil — the fix is different for each.
How to correct it
- Steady, even soil moisture is the single most effective control for blossom-end rot — mulch and regular irrigation matter more than any calcium product.
- On acid soils, lime (or dolomite where magnesium is also low) to raise pH and supply calcium; gypsum supplies calcium without changing pH.
- For groundnut, apply gypsum at the pegging stage into the pod zone — this is a routine practice, not a rescue.
- A foliar spray of 0.5% calcium nitrate or calcium chloride can reduce blossom-end rot on a fruiting crop, but only alongside fixing the watering.
Prevent it coming back
- Irrigate evenly and mulch to buffer soil moisture, especially through fruit set and swelling.
- Keep potassium and magnesium balanced rather than excessive, so they do not crowd out calcium at the root.
- Lime acid soils to a healthy pH, and make gypsum at pegging a standard step for groundnut.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
The bottom of my tomatoes has a black sunken patch. Is it a disease?
No — that is blossom-end rot, and it is calcium deficiency in the fruit, not a fungus or pest. It is almost always caused by uneven watering: the plant cannot move calcium to the far end of a fast-swelling fruit when the water stream is interrupted. Steady irrigation and mulch fix it better than any spray.
My soil test shows enough calcium but I still get the symptoms. Why?
Because calcium deficiency is usually a delivery problem, not a soil-quantity one. Calcium only moves upward with water and cannot be relocated within the plant, so erratic moisture, humidity swings or too much potassium/magnesium can starve tips and fruit ends even on a calcium-rich soil. Fix the watering and nutrient balance, not just the soil calcium.
What are "pops" in groundnut?
Pops are empty groundnut pods that rattle because the kernel never developed — caused by a calcium shortage in the pegging zone at pod-set. Groundnut takes calcium directly into the pods from the surrounding topsoil, so applying gypsum at the pegging stage into that zone is the standard prevention.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.