UNIT IV: Bulb Crops – Onion (Allium cepa L.) and Garlic (Allium sativum L.)
A. ONION (Allium cepa L.)
1. Introduction
Onion is a major bulb crop grown globally and widely consumed. Native to Central Asia, it belongs to the family Amaryllidaceae. In India, it's cultivated in Maharashtra, Karnataka, Madhya Pradesh, Gujarat, and Tamil Nadu.
Uses: Used in culinary preparations, pickles, salads, and as a spice. Dehydrated onions are used in processed food industries.
2. Botany and Taxonomy
- Family: Amaryllidaceae
- Genus: Allium
- Species: Allium cepa L.
- Chromosome number: 2n = 2x = 16
- Growth Habit: Biennial (for seed), cultivated as an annual for bulbs
- Inflorescence: Umbel
- Pollination: Cross-pollinated (entomophilous)
- Bulb: Formed by modified leaf bases (scales)
3. Climatic and Soil Requirements
- Climate: Cool weather during growth and dry weather at maturity
- Optimum temperature: 13–24°C
- Photoperiod sensitivity: Long-day types for temperate zones, short-day for tropics
- Soil: Well-drained sandy loam to clay loam, rich in organic matter; pH 6–7
4. Varieties/Hybrids
- Kharif Season: Agrifound Dark Red, Bhima Super, Bhima Red
- Rabi Season: Pusa Red, Arka Niketan, Bhima Raj
- Export Purpose: Nasik Red, Bhima Shakti
- Hybrids: NHRDF Red, Arka Kalyan
5. Sowing/Planting Times and Methods
- Nursery raised seedlings transplanted at 6–8 weeks age
- Kharif sowing: May–June
- Rabi sowing: October–November
- Spacing: 15 × 10 cm
6. Seed Rate and Seed Treatment
- Seed rate: 8–10 kg/ha
- Seed treatment: Carbendazim @ 2 g/kg + Trichoderma @ 4 g/kg
7. Nutritional and Irrigation Requirements
Fertilizer recommendation:
- FYM: 20–25 t/ha
- N: 100–120 kg/ha, P: 50 kg/ha, K: 50 kg/ha
- Split nitrogen: Half at planting, rest after 30 days
- Irrigation: Light frequent irrigation; critical during bulb formation
8. Intercultural Operations and Weed Control
- Hoeing and weeding: Regular during early stages
- Weedicides: Oxyfluorfen @ 0.3 kg a.i./ha as pre-emergence
9. Mulching
Plastic mulch or organic materials help in moisture retention and weed suppression.
10. Physiological Disorders
- Bolting: Premature flowering due to cold exposure. Bolting refers to a plant's premature shift from vegetative growth to reproductive growth (flowering).
- Splitting of bulbs: Due to excessive irrigation or nutrients
- Sunscald: Direct exposure to sunlight
11. Harvesting
- Time: 100–150 days after transplanting
- Signs: Tops start yellowing and falling
12. Post-Harvest Management
- Curing: 7–10 days under shade
- Storage: Well-ventilated rooms at 30–35°C and low RH
13. Plant Protection Measures
Pests:
- Thrips: Spray Imidacloprid @ 0.3 ml/L. It is an agricultural pest that can damage crops of onions and other plants, and it can additionally act as a vector for plant viruses.
- Onion fly: Drench soil with Chlorpyrifos
Diseases:
- Purple blotch: Mancozeb + Carbendazim. It is caused by the fungus Alternaria porri and results in lesions on onion leaves, stems, and bulbs, often with a purple or reddish-brown appearance.
- Stemphylium blight: Difenoconazole sprays. Caused by the fungus Stemphylium vesicarium (formerly Pleospora allii), this disease thrives in warm, humid conditions and can lead to significant yield and quality losses.
14. Seed Production
- Method: Seed-to-seed or bulb-to-seed
- Isolation distance: 1000 m (foundation), 500 m (certified)
- Seed yield: 800–1000 kg/ha
B. Garlic (Allium sativum L.)
1. Introduction
Garlic is a bulb crop grown for its cloves, used both as a spice and medicine. India is one of the major producers globally.
Uses: Culinary, medicinal (antibacterial, cholesterol-reducing), and pickles.
2. Botany and Taxonomy
- Family: Amaryllidaceae
- Genus: Allium
- Species: Allium sativum L.
- Chromosome number: 2n = 2x = 16
- Bulb: Composed of several cloves enclosed in papery skin
- Reproduction: Vegetative via cloves (no true seed)
3. Climatic and Soil Requirements
- Climate: Cool season crop; prefers mild climate
- Temperature: 12–18°C
- Soil: Well-drained loam to sandy loam, rich in organic matter, pH 6–7
4. Varieties
- Agrifound White
- Yamuna Safed
- G-41
- Bhima Purple
5. Planting Time and Method
- Time: October–November
- Spacing: 15 × 10 cm or 10 × 10 cm
- Depth: 2–3 cm
6. Seed Rate and Seed Treatment
- Clove requirement: 500–600 kg/ha
- Treatment: Cloves treated with Bavistin @ 2 g/kg
7. Nutrient and Irrigation Requirements
Fertilizer recommendation:
- FYM: 20 t/ha
- N: 100 kg/ha
- P: 50 kg/ha
- K: 50 kg/ha
Apply nitrogen in split doses.
Irrigation: At 10–15 day intervals; avoid waterlogging.
8. Intercultural and Weed Management
- Manual weeding and hoeing should be done regularly.
- Mulching with straw or dry leaves helps conserve moisture and suppress weeds.
9. Physiological Disorders
- Bulb sprouting: Occurs due to high humidity.
- Clove shrinkage: Happens in high-temperature storage.
10. Harvesting
Harvest when leaves start yellowing and falling, usually 4–5 months after planting.
11. Post-Harvest Management
- Curing: In shade for 10–15 days.
- Storage: Keep in dry, well-ventilated places, tied in bunches or mesh bags.
12. Plant Protection Measures
Pests: Thrips and onion fly – same control as onion (Imidacloprid spray, soil drenching with Chlorpyrifos).
Diseases:
- White rot: Use Trichoderma and follow crop rotation.
- Purple blotch: Spray Mancozeb or copper oxychloride.
13. Seed Production
Garlic is propagated vegetatively through cloves only. Select healthy, disease-free bulbs from a good crop for next planting.
