Chitosan for crops: what a natural molecule from prawn shells can do
Chitosan is sold to farmers as a biostimulant. Here is what it is, what research shows it can and cannot do, what a cotton trial reported, and how to use it wisely.
Key points
- Chitosan is a natural molecule made from crab and prawn shells. In plants it works mainly as a "wake-up signal" that switches on the crop's own defences, and it can support growth.
- It is a biostimulant, not a fertilizer and not a registered insecticide. Use it alongside good nutrition and pest management, not instead of them.
- In a cotton trial co-authored by Dr. Mathur, sprayed plots were reported taller, with more leaves and about a third fewer bollworms. These figures come from the five best plots, and yield was not measured.
- Buy a registered product, follow its label dose, and compare it against an unsprayed strip in your own field.
What is chitosan?
Crabs, prawns and shrimps carry their skeleton on the outside, as a hard shell. That shell is made largely of chitin, one of the most common natural materials on earth. Insects and many fungi are built from it too.
When chitin from seafood waste is cleaned and treated with a strong alkali, it becomes chitosan. Break chitosan into short pieces and you get chito-oligosaccharides (COS), which dissolve more easily in water.
So chitosan turns a waste product of the fishing industry into a farm input. It is biodegradable and breaks down in soil.
Biostimulant or fertilizer: what's the difference?
Chitosan is a biostimulant. That word is now common on product labels, and it is often confused with fertilizer.
| Feature | Fertilizer | Biostimulant |
|---|---|---|
| What it does | Supplies the nutrients a crop needs (nitrogen, phosphorus, potassium, micronutrients) | Helps the crop take up and use nutrients, and cope with stress such as heat, drought or disease pressure |
| How much is used | Kilograms per acre | Small doses, usually a few grams or millilitres per litre of spray |
| Examples | Urea, DAP, potash, farmyard manure | Seaweed extracts, humic acids, amino acids, chitosan |
| Can one replace the other? | No | No |
A biostimulant cannot feed a hungry crop. A well-fed crop, though, can get more out of each bag of fertilizer when a good biostimulant helps it. They work best together.
Since 2021, biostimulants sold in India have been brought under the Fertiliser Control Order (FCO), and products must be approved before they can be sold. Before you buy, check the pack for registration details.
How chitosan helps plants: what research shows
Scientists have studied chitosan in crops for decades. Reviews of this research describe a few main effects:
- It switches on the plant's defences. The plant senses chitosan much as it would sense a fungus attacking it. It responds by strengthening its cell walls and making its own protective compounds. This "priming" helps it resist disease that arrives later.
- It acts directly against some fungi and bacteria, slowing their growth.
- It can support growth and stress tolerance. Studies report effects on leaf pores (stomata), which can reduce water loss. It has also been tested as a seed coating and as a coating that keeps harvested fruit fresh for longer.
Results vary with the crop, the dose, the timing and the type of chitosan used. Chitosan is a helper, not a cure-all.
What the cotton study tested
The study was published in 2021 in the Journal of Advanced Scientific Research. Its authors are Manjit Kaur and Sanjeev Kalia of RIMT University, Punjab, and Dr. Abhishek Mathur, then at the R&D department of Prathista Industries, Telangana. Dr. Mathur was the third author.
The team did three things:
- Made chitosan and COS from crab and prawn shell waste in the laboratory.
- Tested COS against three crop fungi on lab plates: the fungi behind wilt (Fusarium), collar rot (Sclerotium) and anthracnose (Colletotrichum) in many crops.
- Sprayed cotton in field plots with a chitosan solution at 5 ml per litre and compared them with unsprayed plots. Each plot had 25 plants, both sets got cow-dung manure, and the crop was measured after two months.
What they found
| Measure | Unsprayed | Sprayed with chitosan |
|---|---|---|
| Plant height | 15 cm | 56 cm |
| Leaves per plant | 22 | 33 |
| Fall in bollworm numbers | — | 33% |
Averages of the five best plots, as reported in the paper.
- In the field, sprayed cotton was reported much taller, with half as many leaves again, and with about a third fewer bollworms. The paper does not say which bollworm (pink, American or spotted).
- In the lab, COS slowed all three fungi. It was less strong than the comparison, an anti-fungal medicine used for people.
In simple words: the signs are promising, and they match what other research says chitosan can do. But this one trial cannot tell you how much chitosan will do in your field.
What this study does not tell us
- The field figures are the averages of the five best plots, not of all plots. They show chitosan at its best, not on an average field.
- Yield was not measured. We don't know whether the taller plants gave more cotton.
- No statistics were reported for the field results.
- Key details are missing: where and when the trial was run, the cotton variety, how many times it was sprayed, the strength of the chitosan solution, and which bollworm was counted.
- The fungus test was on lab plates only, not on diseased plants in a field.
The study is a useful early signal. It is not proof that chitosan will control bollworm or raise yield.
Using chitosan on your farm sensibly
- Buy a registered product and follow its label dose. You cannot copy this study's "5 ml per litre", because it does not say how strong its chitosan solution was.
- Spray early. Chitosan primes the plant's defences, so it helps most before disease or pests build up. Follow the crop stages given on the label.
- Check the label before mixing chitosan with other sprays.
- Keep the crop well fed. Chitosan adds almost no nutrients. Base your fertilizer on a soil test.
- Test it yourself. Leave one strip of the field unsprayed and compare growth, pest damage and yield at the end of the season.
Bollworm in cotton: what ICAR-CICR advises
Products sold in India for pest control must be registered with the Central Insecticides Board. Chitosan is not a replacement for proper bollworm management. ICAR's Central Institute for Cotton Research (ICAR-CICR), Nagpur, advises cotton farmers to:
- Monitor with pheromone traps, about 5 per hectare, from around 45 days after sowing.
- Remove and destroy rosette flowers (twisted, half-open flowers that hide pink bollworm larvae).
- Check about 20 green bolls per acre for larvae and damage.
- Sow on time, using short- to medium-duration Bt hybrids recommended for your region; rotate crops and don't stretch the cotton season.
- Spray a registered insecticide only when monitoring shows it is needed, as your KVK or agriculture officer advises.
What comes next
Dr. Mathur has worked on chitin and chitosan for more than a decade, as part of his wider work on natural molecules for farming. As he puts it: "Natural molecules are the future for tomorrow."
NanoKheti does not sell a chitosan product. This article is here to help you judge the chitosan products you see in the market.
