Choosing the right fertilizer for onion is becoming more critical as input costs rise and soil fertility declines in many onion-growing belts of India. Agronomists are now advising a balanced, stage-wise nutrient approach rather than heavy, one-time fertilizer use. Recent field trials and extension advisories show that yield, bulb size, and storage life depend less on “more fertilizer” and more on the right nutrients at the right time. Farmers planning rabi and kharif onion crops should reassess their fertilizer strategy before sowing or transplanting.
What Nutrients Onion Needs Most
Onion is a shallow-rooted crop with high nutrient demand, especially during bulb formation. The most important nutrients are:
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Nitrogen (N): Drives leaf growth and bulb development
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Phosphorus (P): Supports early root growth and plant establishment
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Potassium (K): Improves bulb size, firmness, and shelf life
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Sulphur (S): Essential for pungency, flavour, and oil content
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Micronutrients: Zinc and boron are critical in many Indian soils
Ignoring sulphur and micronutrients is one of the most common reasons for poor bulb quality, even when NPK is applied correctly.
Best Fertilizer Combination for Onion (Recommended Practice)
Based on ICAR and state agriculture university recommendations, the most effective fertilizer program for onion includes both organic and inorganic sources.
Basal application (before transplanting):
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Well-decomposed FYM or compost: 20–25 tonnes per hectare
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Single Super Phosphate (SSP): 250–300 kg/ha
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Muriate of Potash (MOP): 50–60 kg/ha
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Gypsum (for sulphur): 100–150 kg/ha
SSP is preferred over DAP because it supplies both phosphorus and sulphur, which onion needs in large quantity.
Nitrogen application (split doses):
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Urea: 100–120 kg N per hectare
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Apply in 3 splits:
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20 days after transplanting
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40 days after transplanting
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At early bulb formation stage
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Avoid late nitrogen application, as it delays maturity and reduces storage life.
Role of Sulphur: Why It Matters More Than Ever
Soil sulphur deficiency is increasing due to reduced organic manure use and high-analysis fertilizers. For onion, sulphur is not optional.
Benefits of adequate sulphur:
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Better bulb formation
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Improved pungency and taste
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Higher market value
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Reduced incidence of thin, hollow bulbs
Best sulphur sources for onion:
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Gypsum
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Bentonite sulphur
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SSP (partial requirement)
Sulphur should be applied before planting so it is available during early growth.
Micronutrients: Small Inputs, Big Impact
Many onion fields show zinc and boron deficiency, especially in light and alkaline soils.
Recommended practice:
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Zinc sulphate: 25 kg/ha (once in 2–3 years)
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Borax: 10 kg/ha (if deficiency is confirmed)
For quick correction:
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Foliar spray of zinc sulphate 0.5% at 30–35 days
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Boron spray 0.2% during bulb initiation
Unnecessary micronutrient use should be avoided. Soil testing remains the safest approach.
Organic and Bio-Fertilizer Options
For farmers reducing chemical input or practicing integrated nutrient management:
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Neem cake: Improves soil health and controls nematodes
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Vermicompost: Enhances microbial activity
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Azospirillum and PSB: Improve nitrogen and phosphorus availability
Organic inputs alone may not meet full nutrient demand, but they significantly improve fertilizer efficiency when used together with NPK.
Common Fertilizer Mistakes in Onion Farming
Extension officers frequently report these errors:
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Excess nitrogen causing thick neck and poor storage
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No sulphur application despite visible deficiency
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Using DAP repeatedly without organic matter
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Applying all fertilizer at once instead of split dosing
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Ignoring soil test reports
Correcting these mistakes often increases yield without increasing total fertilizer cost.
Conclusion
There is no single “best” fertilizer for onion. The most reliable results come from a balanced fertilizer program that combines organic matter, adequate nitrogen, sufficient phosphorus and potassium, and mandatory sulphur supplementation. Onion productivity today depends on precision, not excess. Farmers who follow soil testing, split nitrogen application, and sulphur-inclusive fertilization consistently achieve better bulb size, higher yields, and longer storage life—outcomes that directly matter in today’s volatile onion market.
