Onion

INTRODUCTION

Onion (Allium cepa) is a vegetable crop which belongs to the family Alliaceous. It is a biennial plant but usually grown as annual. This is because the onion bulb and stem mature within one year while it takes the onion plant two years to fully grow and mature. For this reason, the onions that we commonly eat are harvested during the first year, and the plant is killed rather than being allowed to go to its second year. The onion plant consist of yellowish to bluish-green leaves which grow alternately in a flattened, fan-shaped swathe.The stem of the onion plant from which the roots arise is very short while the bulb consists of fleshy connective scales, which are enclosed in paper like wrapping leaves. The bulb, for which the crop is grown, is formed different and as the onion matures, food reserves begin to accumulate in the leaf bases and the bulb of the onion swells.

Onion is one of the most commonly consumed vegetable crops in the world with China being the number one producer of onions while Japan and India are the second highest producers of green onions and dry onions respectively. Nigeria ranks sixth amongst the top ten producers of green onion, and eleventh in terms of dry onion production. In Nigeria, onion is grown mostly in Kano, Kaduna, Jigawa, Sokoto, Plateau, Bauchi and Kebbi States. In 2012 alone, an estimate of about 240,000 tons of green onions and 1,350,000 tons of dry onions were produced in Nigeria. According to statistics and data research, Nigeria had a world share of 5.5% out of a total of 4, 339,925 tons of green onions produced in 2012 and a 1.6% share of a total of 82, 815, 927 tons of dry onions produced around the world in 2012.

 

Varieties grown in Nigeria

Red Creole: This is a brilliant red short day variety with medium-sized flattened bulbs. It is a popular standard variety in high demand because of its good keeping quality. It produces mainly single onions from transplants and has a pungent taste.

White Creole: This is a short day onion variety. It produces onions with an exceptional great keeping quality. Bulbs are firm, small to medium in size with a thick flat shape. They have pungent smell with excellent dry matter content. It is normally used for dehydration.

Red Tropicana F1 Hybrid: High yielding, large, red, thick-flat onion with firm pungent flesh. It is a highly productive and widely adaptable hybrid that needs good management. It is resistant to common fungal diseases. Keeps well in dry aerated conditions.

Bombay Red: It is a variety for dry and warmer conditions. It is small to medium sized, globe shaped, purplish red and pungent. This is a popular short-day variety in India. It is suitable for dry and warm conditions, with wide acceptance in home gardens. Bulbs are medium-large, semi round in shape and red in color. Flesh is firm and pungent. Medium-late maturity.

Green bunching: Non-bulbing spring onion

Cultivation

• Site selection: the site selected should be flat and free from stumps. The site should also have low atmospheric humidity and clear bright days are also necessary to ensure insect activity for pollination. The optimum temperature requirement for crop development is between 15oC –25oC while for seedling growth is between 20oC – 25oC. Trials have shown that growing onion in warmer weather leads to bulb retardation.
• Land Preparation: Ploughing and harrowing the land to prepare a good and flat seedbed is necessary. If adding manure or composted organic matter then add a few weeks before sowing / planting.
• Soil requirement: Onion can grow on most soil types. However, well-drained sandy-loam soils with PH 6-7 are particularly good for the crop. The soil should be loose and exposed to sunlight. The looser the composition of your soil, the larger your onion bulbs will grow. The soil should be moist before sowing so check the soil the day before sowing and water if the soil is dry.
• Nursery practices: In the tropics the seed is usually sown in a nursery under a mulch cover. In the nursery prepare raised beds maximum 1 m wide and incorporate plenty of well-decomposed compost and fowl droppings. For good germination in the nursery, a well-tilled seedbed with a fine loose surface is necessary. The seedbed should be marked out in rows, which should be about 10-15cm apart in a 120 cm wide seedbed. Then a groove of about 12mm depth is made along each row. To make this process easier, it is advised to use seedling trays for the nursery (click on the link to order for seedling trays https://sence-agricmarket.com/product/seedling-trays/ ). The seeds can now be sown in either of two ways. The first method is to mix the seeds with an equal amount of fine sand. The mixture of sand and seed is then evenly spread in the groove. The second method is to first spread the sand into the groove. The seeds are then spread evenly over the sand in the groove. Hand weeding and watering should continue until the seedlings are 6-8 weeks old when they should be ready for transplanting.
• Transplanting: The land for transplanting should be well prepared and leveled. Seedlings should be transplanted to the field six-eight weeks after sowing in the nursery. When transplanting, spread the roots carefully in the natural position before pressing the soil around. Again space rows about 30cm apart. Sow sets around 10 cm apart as they shouldn’t require any thinning. Dig a small hole for each set and place the set in neck upwards. When covered back up with soil the tip of the neck should just show through the soil surface. Onions could also be planted directly on the field. If sowing on field, sow seed in drills of about 2cm deep with about 1 inch between seeds. If sowing in rows then space the rows about 30cm apart. In the tropics such as Nigeria, only short day or day neutral onion varieties will form bulbs.
• Planting date: Onion setts then they can be planted around Mid to Late March. The dry season onion is normally grown in basins under favourable conditions of day length and temperature when the plant has reached a certain stage of growth.
• Irrigation: The field should be watered twice a month from November through February and weekly in March and April, and during the early part of May. The amount of moisture needed by the plant for irrigation purpose is about 350-550mm. The irrigation frequency is between 5-7 days and the number of irrigation per growing season is about 15-20 times. In addition, good drainage system should be installed to prevent water-logging.
• Fertilizer Application: Onion requires good fertilizer application. Before any fertilizer application a soil test should be done. Fertilizers can be applied four weeks after transplanting. The amount of nutrients required to onion production varies from location to location depending on the inherent soil fertility. For general purposes however, a fertilizer rate of 65 kg N/ha – 40kg p/ha and 45kg k/ha is recommended.
• Weeding: weeding can be done mechanically or chemically by spraying Dacthal herbicide over the beds after planting.

        

• Harvesting: Onions are ready to harvest a week after their tops have started to fall over and are yellowed. It can be harvested by hand pulling or using a fork to lift the onions out of the ground. In firm soils where pulling is difficult, the onion roots can be cut just below the bulbs by using a knife.Take care not to damage the skins as this invites decay organisms in to attack the onion flesh which could cause rotting during storage. Spring onions can be harvested when they are about 30-40cm in height and will store for up to a week in the fridge. To prepare spring onions simply remove the outer set of leaves and wash. Under good management practices, yield of 10-12 tonnes per hectare could be obtained. Onions pulled green keep better in the store than those allowed to ripen off completely in the ground. Bulbs that are harvested when they are too immature may take longer than others to dry properly for storage, and, if the necks are not yet soft, the inner leaves may still be growing and will continue to elongate from the topped bulbs, yielding an unsightly product. Harvesting must be done in dry weather.
• Curing: Before onion bulbs are placed in storage or marketed, the tops are usually removed and frequently also the roots. The neck tissues, and all other moist surface tissue of the bulb where organisms might become established, should be carefully dried before infection can occur. This drying procedure is known as curing. After harvesting and curing, the onion crop is kept in storage regardless of the season they are produced.
• Storage: The harvested onions are preserved in silos. The storage structures consists mostly of bamboo or wood stacks stuffed with grass. Ambient air is allowed to enter the storage structures. The onions could store for up to 6 months in these conditions. It is sad that most Nigerian onion producing communities lack modern processing and preservation plants. These are the areas the Ministry of Agriculture needs to look into. It is also an opportunity for private business people to explore too.

Economic Importance/uses

Onions are generally used for salads, pickling, cooking (such as in soups) and frying (for example, with meat). It also plays an important role in traditional medicine (for example, as a diuretic).

References

1. https://www.naerls.gov.ng/extmat/bulletins/Onions.pdf
2. https://afghanag.ucdavis.edu/educational-materials/principles-of-horticulture/exthortafgonionproductioneastregideappt.pdf
3. https://groworganic.com/media/pdfs/onions-l.pdf
4. https://www.agrifarming.in/onion-farming/
5. https://cagayandeoro.da.gov.ph/wp-content/uploads/2013/04/PRODUCTION-GUIDE-ON-BULB-ONION.pdf

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