Best Fertilizer for Onion in India
Onion is a long duration, shallow rooted crop that rewards careful, well timed feeding with bigger, firmer, longer storing bulbs. Because the roots stay near the surface, the crop cannot cha
Overview
Onion is a long duration, shallow rooted crop that rewards careful, well timed feeding with bigger, firmer, longer storing bulbs. Because the roots stay near the surface, the crop cannot chase nutrients deep in the soil, so fertilizer must be placed where the roots can reach it and supplied in splits. Onion has one feature that sets it apart from most vegetables, a strong response to sulphur, which builds pungency, colour and storage quality. Nitrogen drives early leaf growth, but the timing matters because all the top dressing should finish before the bulb starts swelling, otherwise the crop keeps making leaves and bulbing is delayed. Use the ranges below as a starting point and fine tune them to your Soil Health Card or a soil test, and check the right rate for your region and season with your local KVK.
Recommended NPK dose for Onion
A common recommendation for onion is about 100 to 150 kg N, 50 to 80 kg P2O5 and 50 to 100 kg K2O per hectare, which is roughly 40 to 60 kg N, 20 to 32 kg P2O5 and 20 to 40 kg K2O per acre. Just as important, apply 30 to 50 kg of sulphur per hectare, about 12 to 20 kg per acre, as a basal dose, with the higher rate on soils low in sulphur. The crop removes a large amount of potash and sulphur to fill bulbs, so do not skimp on these. These are starting ranges only. Your Soil Health Card or a fresh soil test will tell you whether your soil already supplies enough phosphorus, potash or sulphur, so you can adjust and avoid waste. Confirm the exact dose for your district with your nearest KVK.
Application schedule
Apply the full phosphorus, full potash, full sulphur and about one third of the nitrogen as a basal dose at transplanting, worked into the bed. Give the remaining nitrogen in two equal top dressings, the first around 30 days after transplanting and the second around 45 days. The critical rule is to finish all nitrogen top dressing before bulb initiation, usually by about 60 days, because nitrogen applied after that delays bulbing and encourages thick necks and poor storage. Where drip is used, fertigation suits onion well since the shallow roots benefit from small frequent doses kept in the moist surface zone. Place top dressing close to the rows and irrigate lightly so the nutrient moves into the root zone without leaching past it.
Organic & bio-fertilizers
Work in 20 to 25 tonnes of well rotted farmyard manure per hectare, about 8 to 10 tonnes per acre, during land preparation, or use roughly 5 tonnes of vermicompost per hectare. Organic matter is especially valuable for onion because it improves the loose, friable surface tilth that shallow roots and bulbs need, and it holds moisture and sulphur where the crop can use them. Apply biofertilizers such as Azospirillum or Azotobacter for nitrogen and a phosphate solubilising bacterium to improve phosphorus availability, either as a seedling root dip at transplanting or mixed into the manure. Adding well composted manure each season steadily improves bulb size and uniformity, and reduces how much chemical fertilizer you need to buy over time.
Micronutrients & deficiency signs
Sulphur is the standout nutrient for onion, not a true micronutrient but applied at micronutrient awareness, because it builds pungency, the deep colour, the firmness and the storage life of the bulb. Always include it in the basal dose. Among the true micronutrients, zinc deficiency shows as yellowing and stunting with pale striping on leaves, corrected with zinc sulphate in the soil or a 0.5 percent foliar spray. Boron deficiency can cause brittle, distorted leaves and poor bulb development, corrected with a light borax spray of about 0.1 percent, applied carefully since excess boron harms the crop. Apply micronutrients only on the evidence of a soil test or clear symptoms, and never guess the dose, since onion is sensitive to over application.
Tips & cautions
Finish all nitrogen top dressing before bulb formation begins, since late nitrogen delays bulbing, makes thick necks and ruins storage. Do not overdose nitrogen at any stage because it pushes leaves over bulbs and softens the crop. Never skip sulphur, which is the single biggest quality lever for onion, especially in soils that have grown many crops without it. Place fertilizer close to the shallow root zone and irrigate lightly so it does not leach away below the roots. If you have drip, fertigate in small frequent doses for the best efficiency. Stop or reduce irrigation as the tops fall over near maturity so the bulbs cure and store well. Build organic matter every season to keep the surface loose and the bulbs uniform.
These are general recommendations. For the exact dose, follow your Soil Health Card / soil test and local KVK, and avoid over-applying urea.
FAQs
Why is sulphur important for onion?
When should I stop applying nitrogen to onion?
What is the NPK dose for one acre of onion?
Why are my onion bulbs small and necks thick?
Onion pests & diseases
Get advice for your soil and crop
Ask farmers Onion price Fertilizer stock