ONIONS PRODUCTION

 Introduction

Onion (Allium cepa Linn), belonging to the Amaryllidaceae family [1], is an important vegetable crop and one of the most widely used ingredients for condiments in sauces, stews, and soups. Between 2010 and 2018, the average annual global production of dry onion was 89.18 million tonnes (t), with an average annual yield of 18.74 t/ha (ha)

Background

• Bulb Onion is one of the most widely grown & consumed vegetables in Nigeria 
• It is a biennial plant but considered an annual because it is harvested in its first growing stage
• It is a profitable crop. However, it requires a lot of labor during transplanting and weeding
• It is an important spice for foods when cooked or served raw
• Used to make pickles or chutneys
• It is rich in Calcium, Iron, Potassium, Vitamin B6 & B9, Vitamin E and has medicinal properties

Variety Selection

There are about five main onion varieties grown in Nigeria. They are:

 

Red Creole: This variety is a brilliant reddish, medium-sized flattened bulb of onions. It is the most popular variety in Nigeria due to its size and longer shelf-life. It usually produce one onion bulb per plant

 

Bombay Red: This variety originated from India. It survives both dry and warm weather conditions. It is globe shaped, purplish red and pungent. It does not mature quickly

.

 

White Creole: It is a short (white) onion variety that produces onions with exceptional great keeping quality. It has small to medium bulb sizes with a pungent smell. It is good for dehydration, suya and salad preparations.

Red Tropicana F1 Hybrid: This is an improved breed. It’s resistant to common fungi diseases, and does well in dry weather conditions. It is high yielding, produces many bulbs per plant. It is the largest with pungent flesh compared to other varieties. It requires special farm management practice, and it has a short shelf life, therefore, requires special storage.

 

Cherry Mountain F1 Hybrid: Cherry Mountain F1 Hybrid is a large, brilliant coloured, dark red Grano onion with excellent storage capabilities. This variety produces round bulbs that are uniform in shape with a refined neck. Highly single centered. Ideal for a fresh market. It is planted before the rains set in.

 

Optimal Ecological Requirements

 

Altitude	0 – 1,900 meters above sea level
Rainfall	500 – 700 mm of rainfall annually
Growing Temperature	15 – 30 0C
Soils	• Fertile and well drained soil • pH range 6.0 – 6.8

 

• Altitude: Onion can be cultivated up to 1,900 m above sea level
• Rainfall: Onions require well-distributed rainfall of between 500 and 700 mm during the growing period. Dry spell is needed at maturity.
• Temperature: The optimum temperature for growth is 15 – 30 0C. If the temperature exceeds 30 0C, maturity is hastened & small bulbs are produced, consequently lowering the yields. When the temperature is low, growth is slowed or the plant may result in flowering. Cold weather is also associated with increased leaf diseases.
• Soil: Onions require fertile and well-drained soil. The optimum pH range is 6.0 – 6.8. Sandy to silty loams with fine tilth are adequate.

Composting 

• During compost making, the organic matter need to be covered to prevent leaching of nutrients 
• Bulb Onion is a heavy feeder and does well in soils with high organic content (manure) 
• Based on the results of the soil analysis, prepare adequate compost for application 
• The recommended rate of application ranges from 10 – 16 tons per acre for Bulb Onion 

 Basal Application 

 Manure incorporation as a basal application 

Basal Application: 

• The manure/compost should be broadcasted (10 – 16 tons per acre) then worked into the soil (incorporated) preferably using a hoe 
• Manure/compost should be applied at least 1 – 2 weeks before transplanting the Bulb Onions 
• Onions respond very well to well decomposed organic manure 

 

A Bulb Onion nursery 

Raising Seedlings 

• Onion is propagated by seed (fresh) 
• Seed rate is 0.8 – 1.2 kg per acre and is sown in a nursery under a mulch cover 

Nursery Establishment: 

• Prepare beds maximum 1 m wide and incorporate well-decomposed compost /FYM 20 kg/m2 and add DAP/TSP 20 g/m2 
• Make rows about 15 cm apart, drill the seed thinly in 1 cm furrows and cover lightly with soil and mulch 
• Germination takes 7-10 days 

Nursery Management: 

• Irrigate the nursery bed regularly 
• After the seed emerges, remove the mulch 
• Prepare a raised cover 
• Manage weeds, pests and diseases

Transplanting 

Recently transplanted Bulb Onion seedlings 

 

Transplanting 

Appropriate Time 

• Seedlings are transplanted 6 – 8 weeks after sowing or at 3-5 well formed leaves when base is pencil thick 

Recommended Spacing 

• The seedlings are transplanted in 2.5 – 3 cm deep trenches at a spacing of 30 cm between rows and 8 – 10 cm between plants (when using furrow irrigation) 

Transplanting Method 

• Soil analysis results should be used to determine the nutrient requirements of the soil prior to planting 
• Irrigate the seedbed prior to pulling out the seedlings 
• Apply 80 kg/acre of TSP 
• Irrigate field well a day before transplanting 
• Carefully pull out the seedlings to avoid damage 
• Cut off 50 per cent of the green tops to hasten take off 
• When planting onion sets, don’t bury them more than one inch under the soil 

Water Requirement 

• Onions require light and frequent irrigation: 
•   At the growing stage: excessive moisture must be avoided 
•   At the bulbing stage: need a substantial amount of water 
•   Watering should be reduced/discontinued towards bulb maturity 
• Lighter soils need more frequent water applications, but less water applied per application 
• Increase the water application as plants and roots increase in size 
• Proper moisture management is important in 
•   Alleviating “Pink Root” 
•   General root health 
•   Vigorous bulb growth 
• Drought stress will cause splitting or formation of double/ multiple bulbs 

 

 

Bulb Onion Seedlings Under Irrigation 

 Strip/banding top-dressing of Bulb Onions 

Top-dressing 

• Soil analysis results should be used to know the 

nutrient requirements of the soil prior to planting 

• Top-dressing can be done in 2 splits 

1st Top-dressing: 30 days after transplanting at 40 kg/acre of CAN 

2nd Top-dressing: 45 days after transplanting at 80 kg/acre of CAN 

• Strip/banding method is preferred over broadcasting as it is more effective 
• Too much nitrogen results in thick necks 
• Top-dressing should be completed before initiation of bulbing 

Unearthing: 

• Unearthing is removal of excess soil around the bulb/loosening soil to allow the bulb to expand or develop well 
• Unearthing can also facilitate the coloring and curing 
• If the soil is hard during bulb formation, loosen the soil to allow bulbs to develop well 
• Unearthing is carried out during 2nd and subsequent weeding and is done by removal of the soil from the bulbs by hand 
• Watch out not to damage or expose the roots 

 

Major Pests 

Pest damage causes a reduction in quality and quantity of produce 

The following are the major pests of Bulb Onion : 

1. Onion Thrips 
2. Onion Fly 

Onion Thrips 

Onion Thrips Identification: 

• Adult thrips are small (0.5 – 2.0 mm), slender and winged 
• Wings are long, narrow and fringed with long hairs 
• Nymphs are white or yellow 
• Both adults and nymphs feed on the base of the plant within the leaf sheaths 

Damages: 

• Attacked leaves have sunken silvery patches 
• Under severe attack, the entire plant appears silvery and later the leaves wither, dry up and die 
• The pest excreta appears as black spots on the silvery leaves 

Control: 

• Keep plants well irrigated since water stressed plants are more susceptible to thrips damage 
• Maintain weed-free plots 
• Rogue heavily infested plants 
• Neem extracts can be sprayed on attacked plants 
• Spray with insecticide, such as Spinosad (Tracer®), Abamectin + Acetamiprid (AMAZING TOP 100 WDG® PHI:21 days), Acephate (ASATAF SP® PHI: 3-7 days) 

Onion Flies 

Onion Flies Identification: 

• The onion fly maggots measure 8 mm long and are white cream in color 
• They are the most destructive stage of the fly 

Damages: 

• They eat the lateral roots causing tunnels into the taproot, plants become shriveled or eventually die 
• They are also found inside developing onion bulbs and their feeding exposes the plant to infection by diseases like Bacterial Soft Rot 

Control: 

• Practice crop rotation 
• Use well decomposed manure/compost 
• Practice field sanitation: remove and destroy infested plants 
• Carefully plough in crop residues immediately after harvest 

Major Diseases 

Disease infection leads to reduction in quality and quantity of produce 

The following are the major diseases of Bulb Onion in Nigeria : 

1. Onion Downy Mildew 
2. Purple Blotch 
3. Rust 
4. Pink Root 
5. Neck Rot 

 

Onion Downy Mildew 

Symptoms of “Onion Downy Mildew” infection on a Bulb Onion leaf 

General Descriptions: 

• The disease is caused by a fungus 
• It is prevalent in cool, humid and poor drainage conditions 

Symptoms: 

• Formation of lesions near the tips of the 

older leaves, 

• Yellow patches covered with gray wet 

fields 

• Leaf tips shrink, turn pale brown and later die 

Control: 

• Field hygiene 
• Crop rotation 
• Use tolerant varieties e.g. Red Pinoy F1 
• Use of fungicides e.g.) Mancozeb (Cadillac®, Dithane M45® etc.) 

  

Purple Blotch 

Purple Blotch General Description: 

• The disease is caused by a fungus 

Symptoms: 

• Small white spots on the foliage 
• Under moist condition, the spots rapidly increase to large purplish blotches often surrounded by a yellow to orange border 
• Lesions extend to girdle the leaf which leads to its collapse 
• Infection may spread to the bulb, where it may cause a wet, 

orange rot starting at the neck Control: 

• Use resistant varieties e.g. Red Passion F1 and Red Pinoy F1 
• Crop rotation 
• Field Sanitation: remove crop remains after harvest, do not leave volunteer plants in the field 
• Avoid over fertilization 
• Recommended spacing and good drainage to decrease humidity in the plant stand 
• Use of fungicides such as Mancozeb (Dithane M45®) Difenoconazole ( Domain 25% EC®), 
• Propineb + Cymoxanil (Milraz WP 76®) 
• Eugenol (e.g. Explorer 0.3 SL®) 

 

Rust 

Symptoms of “Rust” infection on a leaf of Bulb Onion 

General Description: 

• The disease is caused by a fungus 
• High humidity, high temperatures and dense plant population favor the disease development 

Symptoms: 

• Small reddish dusty spots (pustules) on leaves 
• Heavily infected leaves turn yellow and die prematurely 

Control: 

• Crop rotation 
• Application of proper agronomic practices: proper nutrition and spacing 
• Use of fungicides: 
•  Mancozeb (Dithane M45) 
•   Difenoconazole (Domain 25% EC®) 
•  Eugenol (Explorer 0.3 SL®) 

 

Pink Root 

Infection with “Pink Rot” on the roots and leaves of a bulb onion 

Pink Rot Symptoms: 

• Similar to nutrient deficiencies or stress associated with extremely dry conditions 
• Light pink to yellowish-brown discoloration on roots that becomes dark pink then red and eventually purple 
• Under advanced stages, roots eventually shrivel, become brittle and die 

Control: 

• Good management practices that reduce 

plant stress 

• Crop rotation 
• Use tolerant cultivars e.g. Red Passion F1 

 

Neck Rot 

Bulb Onion “Neck Rot” Symptoms 

General Descriptions: 

• Disease visible when onions are in store 
• Caused by a fungus which enters the onions through wounds or cracks in the fleshy neck part of the bulb. 

Symptoms:

• Top part of the bulb will turn browner and the skin will be darker brown. 
• Top of the bulb will be softer than the lower parts. 
• Gray mold and sometimes speckled with small black spots will appear, and the bulbs will deteriorate even further. 

Control: 

• Use fungicide treated seeds or sets 
• Avoid damaging onion bulbs at or during harvest 
• Don’t bend over foliage to hasten drying out 
• Only harvest onions when the necks have ripened and fallen over on their own accord. 
• Avoid using high nitrogen fertilizers 
• Crop rotation at least 3 years 
• Dry the bulbs out thoroughly after harvest 
• Good ventilation is more important in the drying process than the sun. 
• Store only bulbs with dried out thin necks 
• Store bulbs in a cool and dry place 
• Sort out bulbs which show signs of rot. 

 

Harvest 

• Harvesting can be done 90 – 150 days after transplanting depending on the variety 
• Bulb Onions are ready for harvesting when the leaves collapse or when 75 % of the tops of the crop have dried and fallen over 
• Leaf tops begin to discolor, bend and dry towards the ground 
• Reduced thickness of sheath leaves surrounding the bulbs (papery membranous cover) 

 

 

Post-Harvest Handling And Curing 

What is “Curing”? 

Curing is a technique used to remove moisture from bulb necks and outer leaves. 

The main objective is to prevent moisture loss in order to extend shelf life and fend off disease attacks. This can be accomplished in the field or in a protected area away from inclement weather, such as rain or direct sunlight. 

Field Curing 

Curing can be done in the field if the maturity and harvesting coincides with dry months 

Harvested onions are placed in rows with leaves partially covering the bulbs to prevent sunburn or greening 

Onions are then left in the field until the outer leaves and neck are completely dry and papery 

Field curing can take 2 – 3 weeks depending on the environmental condition 

Protected Curing 

Drying of Onions in a protected environment 

Curing is done in a warm, dry and well ventilated location protected from direct sunlight and rain 

The process involves the following: 

•  Removal of excess soil 
• Trimming of foliage leaving 2.5cm of section of stem at neck 
•  Placing onions in single layer in large flat tray 
• Onions can also be cured by tying tops of bulbs in bunches and hanging on a horizontal pole in well ventilated shade 

 

Sorting 

Bulb onions are sorted to get rid of the following things before storage: 

•   Onions with thick necks 
•   Onions which have bolted 
•   Injured onions 
•   Decayed onions 
•   Doubles and small bulbs 

Grading 

Before and after storage, grading needs to be completed.

 Onions are graded three times for the domestic market: large, medium, small. 

 Bulbs must be: 

•  Intact with firm flesh which is not exposed 
•   Clean and free from visible foreign matter 
•   Sufficiently dry with the first two outer skin and stem fully dry 
•   Free from abnormal external moisture 

Containers & Packaging Materials 

Bulk onions should be packed or stored in containers with good ventilation, like onion nets. 

 

Marketing

In Southern Nigeria, there is a ready market for onions. Nigeria produces 75% of its onions, which are consumed in the south. The remaining 99% of the onions are grown in the north and exported down the nation. Producing in the South brings you closer to the market, which lowers marketing expenses and waste. More profit results from this. Additionally, Northern produce (the Northern off-season) matures before Southern produce. At this period, onion is usually scare and costly. 

It is simple to sell onions. You can sell to distributors, off takers, or at retail markets that are dotted throughout South Africa that offer fresh farm produce.

 

Nigerian onions may be grown profitably because of the favourable environment and strong local demand. Expenses include of labour, fertilisers, fungicides, insecticides, and seeds. For those with limited resources, smaller-scale production is advised. Prices per kilogramme can vary from 150 to 200 Naira, while yields can range from 16 to 30 tonnes per acre. Per acre, net revenues might vary from 500,000 to 1 million Naira. The best practises include planting early, harvesting bulbs at local markets, applying drip irrigation, weeding often, curing bulbs after harvest, and taking into account value-added services like packing, grading, and cleaning.