Nutrient Management During Onion Bulb Development

Onion is an essential commercial crop, with its market value largely depends on bulb size, weight, shape, shine, and shelf life. Proper nutrient management throughout the onion growth cycle, especially during the bulb development stage, is crucial to achieving high-quality yields. The onion growth cycle consists of three phases: vegetative growth, reproductive phase, and maturity. Each stage requires specific nutrient inputs to ensure better crop establishment, nutrient uptake, and overall plant health. This article highlights the role of essential nutrients and appropriate fertilization strategies to improve onion bulb size and weight, enhancing farmers’ income and market competitiveness.

What are the Growth Phases of Onions?

Vegetative Growth Phase:

• Focuses on root development, crop establishment, and vegetative growth.
• Adequate phosphorus and potassium supply ensures strong plant growth and better nutrient uptake.
• Improved vegetative growth leads to enhanced nutrient flow during the reproductive phase.

Reproduction Phase (Bulb Initiation and Development):

• Nutrient allocation shifts from vegetative parts to bulb formation.
• Balanced phosphorus and potassium supply aids in energy transfer, cell expansion, and improved bulb size and weight.
• Secondary nutrients like calcium and sulphur enhance the structural integrity and pungency of the onions.

Maturity Phase:

• Emphasis on balanced nutrient management to improve bulb quality, weight, and shelf life.
• Proper water and nutrient management is critical to prevent rotting and ensure storage stability.

Importance of Nutrients During Bulb Development Stage in Onion

Primary Nutrients:

• Phosphorus (P): Enhances energy transfer, nutrient uptake, and movement towards the bulb.
• Potassium (K): Maintains water balance in bulbs, improving the size, shape, weight, shine, and shelf life.

Secondary Nutrients:

• Calcium (Ca): Strengthens cell walls, aids in proper bulb initiation, improves shape, and enhances storage life.
• Sulphur (S): Enhances pungency, taste, and overall onion quality.

Micronutrients:

• Zinc (Zn): Promotes auxin production, cell expansion, and uniform bulb development.
• Boron (B): Facilitates calcium movement, cell elongation, and proper bulb shape.

Nutrient Management in Onion During Bulb Development

During the vegetative growth stage, establishing a strong foundation for plant development is crucial. PeKacid 0-60-20 is highly effective in fulfilling the phosphorus and potassium requirements necessary for early growth. What makes PeKacid unique is its compatibility with calcium, magnesium, and zinc, which enhances nutrient availability. It also works effectively in solubilizing insoluble phosphorus and calcium, making them readily accessible for plant uptake. Applying PeKacid at a rate of 5 kg per acre (two doses) through fertigation or drenching, significantly improves phosphorus, potassium, and calcium absorption from the soil. To further optimize plant growth, the use of FertiFlow 12-6-22+12CaO provides a balanced supply of nitrogen, potassium, and calcium, which strengthens root tips, enhances cell division, and supports plant structure. Applying 5 kg per acre of FertiFlow 12-6-22+12CaO by two doses, with a 5-6 day interval between applications, ensures a steady nutrient supply. This combined approach not only meets the NPK requirements but also provides crucial calcium and micronutrients, essential for robust vegetative growth.

As the crop transitions into the reproductive and maturity stages, the focus shifts towards improving bulb size, weight, and overall quality. A strategic application of PeKacid 0-60-20 along with FertiFlow Potassium+ 8-0-47+7S ensures optimal potassium supply, which directly influences onion size, shape, shine, and shelf life. Potassium plays a key role in regulating water balance, which is crucial for extending storage longevity. Additionally, sulfur in FertiFlow Potassium+ 8-0-47+7S enhances pungency and color, contributing to better market value. While SOP (0-0-50) is commonly used to meet potassium requirements, FertiFlow Potassium+ 8-0-47+7S offers a more balanced nitrogen-to-potassium ratio, ensuring improved nutrient uptake efficiency. Since potassium absorption is enhanced by nitrogen during maturity, this balanced approach leads to superior results over SOP alone.

Furthermore, micronutrient application plays a vital role in onion cell division and overall growth. A 1-liter dose of Zinc Suspension (39.5% EC) per 200 liters of water, applied via fertigation or drenching, enhances plant metabolism and development. Meanwhile, boron application (250 ml of liquid Boron 10% per 200 liters of water) during both vegetative and reproductive stages ensures proper bulb initiation and cell expansion. Since calcium moves primarily from the root zone upwards, Liquid Calcium at 1 liter per 200 liters of water should be applied via fertigation or drenching to prevent calcium deficiencies like bulb splitting and poor shelf life.

In India, a small fraction of onion cultivation is under drip irrigation, while the majority of farmers still rely on traditional basal and foliar applications to meet the crop’s nutrient requirements. To enhance nutrient efficiency and maximize yield, ICL introduces its latest patented adjuvant technology in the Nutrivant series of foliar fertilizers.

During the bulb development stage, the application of Nutrivant Fruit (12-5-27+8CaO+Micronutrients) provides a balanced supply of NPK along with Calcium, which is essential for uniform bulb formation and improved storability. Additionally, the use of Nutrivant Peakvant (0-49-32) enhances bulb firmness, quality, and overall yield. For better results, it is recommended to apply two foliar sprays of Nutrivant Fruit and Peakvant at an interval of 7-8 days.

Furthermore, to enhance micronutrient availability, a foliar application of Chelated Zn EDTA (1 g/L) and Boron 20% (0.5 g/L) is recommended. These micronutrients play a vital role in cell division, root development, and overall plant metabolism, ensuring a healthy crop with a high marketable yield.

Conclusion:

Achieving higher onion yields with increased bulb size and weight requires a balanced supply of essential nutrients like phosphorus, potassium, calcium, sulphur, boron, and zinc. These nutrients are critical for energy transfer, cell division, bulb expansion, and overall storage quality. Proper nutrient and water management helps prevent issues like bulb rotting and uneven development. Selecting the right fertilizers enhances nutrient availability and uptake, leading to improved onion yield, quality, and market value. By adopting precise nutrient management strategies, farmers can significantly enhance onion productivity and profitability, ensuring high-quality produce that meets market demands.

References:

P.K.S. Jayathilake, I.P.Reddy, D. Srihari’, K.R. Reddy’ and G. Neeraja¹, Integrated Nutrient Management in Onion (Allium cepa L.), Tropical Agricultural Research Vol. 15: 1-9 (2003)

Khalid Mahmud Khokhar, Mineral nutrient management for onion bulb crops, The Journal of Horticultural Science and Biotechnology Volume 94, Pages 703-717, 2019

Talwar Dilpreet¹, Singh Kulbir¹, Sardana Varinder² and Singh Jagdish^3, Growth, Yield and Quality of Onion as Influenced by Integrated Nutrient Management, International Journal of Agriculture Sciences ISSN: 0975-3710&E-ISSN: 0975-9107, Volume 8, Issue 51, 2016, pp.-2295-2298.