ONION PRODUCTION

1. Introduction

The onion is a biennial vegetable that is grown twice annually in Rwanda. Onions are produced in almost all the provinces mainly in Northern and Southern provinces of Rwanda. Rwanda is currently producing more than 20,000 MT per year, mainly red, yellow and white onions A hundred grams of onion contains about 30 g calcium, 0.5 mg of iron, vitamin B, 0.2 mg of riboflavin, 0.3 mg nicotinamide, and 10 mg ascorbic acid (vitamin C). In most Rwandan communities, onions are incorporated in almost all recipes as a major ingredient. Onions can be used raw as a vegetable salad and cooked as a flavoring in soups, stews and is pickled. Onions can also play a role in traditional medicine such as diuretic. It is made from finely ground, dehydrated onions, mainly the pungent varieties of bulb onions, and has a strong odour. Onion powder is a seasoning widely used when the fresh ingredient is not available. Being dehydrated, it has a long shelf life

Figure 1 Onion Production in a farm

Varieties of onion

Variety	Maturity period	Yield potential	Varietal traits
Bombay Red Source: E-hinga	150 days	16 tons per acre	Early maturing, deep purple red color It produces small to medium onions Very pungent onion Popular with farmers and the market Excellent shelf life
Red Creole Source www.royalseed.biz	150 – 180 days	16 tons per acre	Deep red color Most preferred variety grown in the northern and western part of Rwanda. Yields big onions Well adapted to diverse climatic conditions Maturity 150 days from transplant Ideal onion for the fresh market Good storage quality
Green (evergreen) bunching Source : www.fruithillfarm.com	110 days	3 - 3.5 tons per acre	-It is a non-bulbing spring onion. -The leaves are tasty, attractive and dark green in color. -It matures early and it is grown for the stems and leaves rather than bulbs. -It is tolerant to sun scotch. -It is recommended for salads and fresh market.
Red Passion F1	90-120 Days	25tones per acre	-It is deep red in color. -The bulbs are uniform and medium sized bulbs. It is tolerant to Pink rot and Purple blotch disease. It has excellent curing qualities and storage.
Pink F1	90 – 100 Days		-It is dark red in color. -It is widely adaptable. -The variety has a high disease tolerance.
Red nice F1 Source: www.smartfarmingug.com	110-120 days	25-30 tons per acre	-It is dark red in color. -It has a wide adaptability -It is highly pungent with good curing quality. . -It is tolerant to purple blotch disease. -It can be stored for a long period up to 6 months.
Red piney Source: www.royalseed.biz	90 days	25-30 tons per acre	-Can be grown in rain fed or irrigated conditions. -It has a strong pungent. -It has a long shelf life of up to 6months when stored at room temperature. - The bulbs are deep red in color and have a high market demand - It is resistant to downy mildew and purple blotch.

2. Agro-ecological requirements

Soil The crop performs best in a well-drained fertile soil. The optimum soil pH range of 6.0 – 7.5 is required since onions are very sensitive to highly alkaline soils.

Rainfall: Onions do well in areas with an annual rainfall of between 650-800mm. Where rainfall is insufficient, irrigation should be done to ensure consistency in moisture content.

Temperature: Onions require an optimum temperature of 13-24⁰C and 18-26⁰C. This temperature is essential for vegetative and bulb formation stages of the crop. In seed production, the crop requires an optimum temperature of 20-25⁰C. Maturity of onions is hastened if the temperature greatly exceeds that required for bulbing. This leads to low yields because the bulbs do not grow to maximum size.

Altitude Onion does well up to an altitude of 2500m above the sea level.

3. Seedling and nursery establishment

Onion seedlings in nursery Source: www.ics-agri.com

In the East Africa onion is propagated by seed while in temperate regions, they are propagated by sets (immature bulbs ripened during the previous season). The seeds are first raised in a nursery bed before they are transplanted in the main field. Nursery beds should be made on a well-prepared land. The nursery bed should be raised, 1m wide and any desired length. Add well-decomposed farmyard manure and rock phosphate and mix well with the soil.

Make planting rows 15cm apart, sow the seeds and cover them lightly with the soil. The seed rate for onions is 2-3 kg per ha. The nursery bed should be well irrigated for the first 10 days. The mulching material should be removed after the seeds have emerged. Seed germination occurs after 7-10 days after sowing.

4. Seed multiplication and certification requirement

Onions require about 10 months in seed production to complete the cycle from seed to seed. In order for seeds to attain a 70% seedling emergence, temperatures of 13⁰C are required The seeds are directly sowed in the main field. This is a cheaper method of seed production since there is reduced labor of transplanting. Ensure that the minimum isolation distance is observed between the onion field and other nearby fields especially the ones having crops of the same family as onions. Field inspection should be done by RALIS to ensure that the seed grower is following the right standards for seed production.

Onion flowers: Source www.orientalseed.com

Onion seeds Source: www.exportersindia.com

5. Integrated soil fertility management

Onion plants require high amount of micronutrients and a moderate requirement for N-P-K.. It is a shallow rooted crop hence fertilizer application should be done near the base of the crop. Farmers should avoid application of fresh manure to the crop because it will cause the plants to develop thick necks and too much leaf at the expense of bulb formation. The fertilizer application requirements for onions vary with factors such as temperature, variety, spacing, soil type and available water. Fertilizer application should be done according to the soil test results.

Nitrogenous fertilizers such as urea should be added to correct the condition

Deficiencies

a)Nitrogen

The leaves of plants with nitrogen deficiency turn yellowish green, upright curled, wilted and dwarf. The symptoms develop first on the older leaves and gradually move to the younger leaves. The tissue above bulbs become soft at maturity.. Plants become more susceptible to water stress and they wilt. Premature leaf fall is common in plants with nitrogen deficiency. Nitrogen deficiency can be managed by adding organic matter in form of manure, compost, peat that improve the soil structure consequently improving the plant’s capacity to retain water and nutrients.

Nitrogen deficient onion Source: plantix.net/plant-disease

b) Phosphorous

Phosphorous deficient plants source www.agri.wa.gov.au.

The symptoms appear at all stages of development but are more noticeable in young leaves. Phosphorous deficiency leads to stunted plant growthIn a severe case, the stems and petioles have a dark green to purple discoloration. The tips of older leaves appear scorched. Phosphorous deficiency can be corrected by adding organic matter such as manure, organic mulch or incorporating crop residues to the soil. Fertilizers containing phosphorous such as NPK should also be applied Soil testing is necessary to know the exact amount of nutrients one should apply.

c) Zinc

Zinc deficient plant Source: https://expertsystm.wixsite.com

Zinc deficiency restricts plant growth, while leaves exhibit interveinal necrosis with the main veins remaining green in case of heavy deficiency. The yellowing of leaves starts from the margin, occasionally the leaves cluster around the stem, and leaves appear twisted and bend outwards. The deficiency can be controlled by applying organic manure to the field before transplanting. Onions are very sensitive to zinc deficiency and application of foliar sprays of zinc sulphate.

d)Potassium

Potassium deficient plant source: https//expertsystm.wixsite.com

Potassium deficiency symptoms mostly are seen on the young leaves because potassium is very mobile. The Leaves become dark green and erect while the tips burn, there is leaf necrosis and yellowing of the older leaves. Leaf curling and stunted growth makes the plants more susceptible to diseases and stresses such as drought and frost. Potassium deficiency can be controlled by adding organic matter inform of wood ash at least once a year. Potassium based fertilizers can also be applied as a base fertilizer during field preparation and at flowering stage.

e)Iron

Iron deficient onion plant https://www.yara.in

Dandelion plant http://survivalgardener.com

The deficiency symptoms start from the younger leaves. Iron deficiency will lead to complete yellowing of young leaves when the deficiency is not corrected, the whole leaf turns whitish yellow with brown necrotic spots forming on the leaf blade. The leaf veins remain green leading to retarded plant growth due to reduction of chlorophyll content. This can be corrected by application of organic manures can provide iron to the plants and also plant dandelions near the onion field because it makes iron available to the nearby crops and application of iron based fertilizers.

6. Regenerative Agriculture

Mulching : This aims at reducing the soil moisture loss to the atmosphere. It also helps in weed control by smothering the weeds. If organic materials such as clean plant materials are used it can lead to increased nutrients in the soil.

Plastic mulch

Source: http://farmbizafrica.com

Organic mulch

Source Isoko: https://greenfusestock.photoshelter.com

Crop rotation Crop rotation is necessary in onion production because it can help minimize pests and diseases. Crop rotation should be done with crops that are from different families.

Intercropping Onions can be intercropped with other crops from a different family. Onion plants are known to keep away some insect pests such as the diamond back moth in cabbage.

Onions intercropped with carrots Source : https://en.wikipedia.org/wiki/Polyculture

7. Land Preparation

Choose the planting site where no onion family crop has been cultivated for at least 2 years.
Land preparation should start as soon as the seeds have been planted on the nursery bed.
Clear the land of all the vegetation including the weeds and all the volunteer crops.
Burning the vegetation is highly discouraged as this will lead to destruction of useful soil microorganisms and lower the soil fertility.
Remove all the obstacles including the tree stamps and stones to make other farm operations easier.
Land can be ploughed by the use of hand tools such as a hoe.
It can also be done by the use of ox drawn or tractor drawn ploughs if the farmer has a large piece of land.
Harrow the soil to break all the large soil clods to attain a fine tilth.
The soil should be well levelled to ensure uniform crop growth.

8. Fertilizer application

Fertilizer requirements for onion production vary with the soil type.
Application of well-decomposed farmyard manure at the rate of 11 to 22 t/ha can supply nutrients and fulfill early season N requirements
With efficient irrigation, a total of 260 kg/ha of N should maximize yield on most mineral soils, with less needed on soil types with high residual N.
Nitrogen should not be applied in excess because it will lead to excessive vegetative growth hence delayed flowering.
Too much nitrogen can also promote unwanted secondary growth.

9. Transplanting

The seedlings are ready for transplanting 6-8 weeks after sowing or when they have a base as thick as a pencil and are about 15cm tall with 4 to 5 leaves.
Transplanting should be done early in the morning and watered immediately or later in the evening to avoid wilting due to evapotranspiration.
The nursery bed should be well watered one hour prior to transplanting to avoid root damage during uprooting of the seedlings. The seedlings are planted in the main seedbed as soon as they are uprooted from the nursery bed at a spacing of 8x10cm.

Crop development stages ibyiciro byo gukura kw’ igihingwa Source isoko: www.haifa-group.com

10. Crop management

Thinning : Involves the removal of excess seedlings to attain the correct plant population and to avoid competition for space, light and nutrients.

Source Isoko: www.vegetablegardener.com

Weeding Onion plants have a poor competing ability with the weeds hence weed control is very crucial. The field should be kept weed free at all times. Weeding can be done manually or by spraying with selective herbicides that will not affect the useful insects.

Weeding

Source:

Irrigation On light sandy soils irrigation is necessary. Irrigation could be either overhead or on drip. Onions at the bulbing stage need a substantial amount of water, but excessive moisture must be avoided during the growing season.

Sprinkler irrigation

Source Isoko: startuptipsdaily.com

Drip irrigation

Source Isoko: irrigazette.com

11. Pest and diseases control

Physiological disorders

Bolting This is the production of flower stalks at the expense of bulb formation and enlargement. The bolted onion bulbs should be harvested as soon as possible and consumed immediately because they cannot be stored. Bolting is caused by abnormal temperature fluctuations and cold weather stress, loose soil and over fertilization. The disorder can be managed by choosing the right variety according to specific climatic conditions, planting at the right time and fertilizer application in the right amounts.

Onion bolting Source: kb. gramophone.in

2.Onion greening This is caused by exposure of bulbs to sunlight for extended period of time whereby they form chlorophyll. Excessive or late application of nitrogen fertilizer can cause delayed maturity leading to onion greening. It can be managed by fertilizer application at the right time and in correct amounts. Avoid curing onions for long periods.

Onion greening

Source: expertsystm.wixsite.com

3. Sunscald: This disorder is a problem in young seedlings and in bulbs. The damage is caused by very high soil temperatures where the seedling tissues are damaged resulting in shriveling collapsing of plants. On bulbs, the affected tissues become bleached, soft and slippery. When the affected areas dry, they result in brown scales that are necrotic. It can be managed by curing onions at temperatures below 29⁰C.

Onion sunscald Source: www.science.oregonstate.edu

4. Pinking: This involves the formation of a pink color, which normally occurs when the onion bulb is bruised, especially during harvesting and post-harvest handlingThe discoloration reduces the quality and salability of the onion bulbs. Farmesrbshould harvest onion bulbs more carefully to avoid bruising them.

Onion pinking disorder Source: Howard F. Schwartz, Colorado State University, Bugwood.org

12. Pests of Onion

Pest

Damage

Management

Onion thrips

Source: Chris Wallwork Agrii (www.aafarmer.co.uk)

-The thrips pierce the upper surface of the leaves and feed on the plant sap.

-This leads to formation of silvery patches on the leaves. The excreta of the thrips are visible as small black dots on the silvery leaves.

- Under heavy infestations it can lead to browning of the leaf tips, stunted plant growth, distortion of leaves and bulbs, and reduction in bulb size

-Keep plants well irrigated because dry plants are more susceptible to thrips damage.

-Keep the field weed free because they can be alternate hosts for thrips.

- Remove the heavily infested plants and plant materials and destroy them.

Leaf miners

Source: gardener.shoutwiki.com

-They feed on the leaves leaving minis or tunnels on the leaves which may cause rejection of onions in the market.

-They can be controlled by the natural enemies, especially parasitic wasps.

-Spraying with pesticides is not highly recommended because leaf miners have the ability to develop resistance to pesticides in a short period.

Onion fly

Source: gardening.which.co.uk

-Attacked leaves wilt and the leaves turn bluish.

-The plants become shriveled and die eventually.

-Onion fly maggots feed just above the base of seedlings killing them.

-Avoid planting in soils that have high amounts of undecomposed organic matter, or in very weedy conditions.

-Allow enough time for organic manure to decompose well before planting.

-Avoid planting successive onion crops.

-Practice crop rotation.

-The infested plants should be removed and destroiyed or burnt.

cutworms

Source : bulletin.ipm.illinois.edu

-The caterpillars cut and eat the stems of young seedlings.

-Heavy infestations can lead to total crop loss, if not controlled.

-Destroy all the plant residues from a recent crop and avoid planting in fields coming out of pasture.

-Keep the field weed free before and after planting.

13. Diseases of Onion

Symptom

Management

Disease

Damping off

Source: http://vikaspedia.in

-It is a soil borne disease which attacks the seeds and seedlings. Infected seedlings fall over and die due to breakdown of plant tissues at the soil level.

-Sterilize the soil before planting.

-Regulate watering. Avoid overcrowding of seedlings in the nursery.

Downy mildew

Source Isoko: www.greenlife.co.ke

-Diseased leaves turn pale-green, then yellow, and collapse and eventually die.

- This disease is favored by cool and humid weather.

-Use clean and healthy seeds or sets.

-Use resistant varieties.

-Practice crop rotation with crops of different families.

-Use a wider spacing to reduce humidity and downy mildew.

Purple blotch

Source: www.greenlife.co.ke

-The infected leaves have small water soaked lesions with whitish centers.

-The leaves may turn yellowish-brown, lose erectness and eventually wilt, if the disease is not controlled.

-Use varieties that are more resistant.

- Increase spacing between plants - - Treat the seeds before planting. - - Practice crop rotation.

- Remove all crop debris and plant in well-drained soils.

- Use fungicides when the disease is very severe.

Onion rust

Source: www.namayasai.co.uk

-Whitish to yellow spots appear on the leaves, which enlarge as disease progresses which become orange and develop into black lesions overtime.

- It leads to stunted bulb formation under heavy infestation.

-Practice crop rotation and keep the field weed free.

Botrytis neck rot

Source: blog.pestprophet.com

-It affects the onions in store but it originates from the soil.

- The diseased onion necks become watery, brown and hardens to wizened papery leaves

- In case of high humidity a grey mold may grow between the onion layers.

-Timely applications of nitrogen fertilizers

-Harvest the crop when it is well matured and ensure proper curing.

Bacterial soft rots

Source: Lindsey du Toit, Washington State University (mtvernon.wsu.edu)

-It causes huge losses in storage.

-At this stage, the affected tissues are water-soaked and pale yellow to light brown.

- As the rot progresses, the invaded fleshy scales become soft.

-Allow the onions to mature well before harvesting.

-Avoid bruising during harvesting and packaging.

-Onions should be stored in well-ventilated stores to avoid accumulation of moisture on the surfaces of bulbs. They should be stored at 0 degree Celsius and at a relative humidity (RH) of 65-70%.

14. Harvesting, post-harvest handling and storage of onions

a) Harvesting

Manual harvesting is the most common practice in most developing countries .Depending on the variety and the prevailing environmental conditions, onions can take about 4-5 months to mature. This is normally carried out by levering the bulbs with a fork to loosen them and pulling the tops by hand. In developed countries, especially in large-scale farms, mechanical harvesting is commonly used. The harvesting techniques adopted are influenced by weather condition at harvest time. In areas where warm, dry weather occurs reliably, the curing and bagging of the crop can be done in the field (two phase harvesting). In wetter, temperate regions, mechanical harvesting and artificial heating and ventilation for drying are essential for reliable production of high quality bulbs on a large scale. The following steps are followed during two-phase harvesting of onions:
Onions should be harvested one week after 50% of the leaves have fallen.
The onions are mature when; the leaves turn yellow, the bulbs turn red and have attained a maximum size.
In small-scale farming, harvesting is done by pulling out the bulbs.
Mechanical harvesters can also be used in large-scale onion farming.

mowing the leaves (if necessary);

stubbing, undercutting and sieving the onions to remove stones and clods;

roll the soil in the row to get a plane surface;

drying the bulbs (windrowing) 8 to 10 days in the field;

turning the bulbs 1 to 2 times;

harvesting, sieving and hand grading, overloading into a trailer or in crates; and

transport.

Mature onions ready for harvesting source smartbusiness.co.ke

Harvested bulbs are placed in containers (basket, bins) or tied into bunches and placed directly on the floor of a trailer for transport. These trailers can be pulled by an animal (such as donkey) or mechanical transport such as a tractor. Both packaging and transport systems must be selected to ensure minimum handling damage to produce. Hard surfaces should be cushioned with leaves, foam or other appropriate force decelerators. The following aspects should be observed when harvesting:

Stop irrigation at maturity- 1 (soils with low water retention) or 2 weeks (soils with high water retention) before harvest to prevent bulbs from being waterlogged.

Harvest bulbs during the cooler part of the day (early morning & late evening).

Manual harvesting- levering the bulbs with a fork to loosen them and pulling the tops by hand

Avoid damaging the bulbs

b) Drying and curing

Both curing and drying remove excess moisture from the outer layers of the bulb prior to storage. The dried skin provides a surface barrier to water loss and microbial infection, thereby preserving the main edible tissue in a fresh state. Drying also reduces shrinkage during subsequent handling, reduces the occurrence of sprouting, and allows the crop to ripen before fresh consumption or long-term storage.

This process of dehydration is sometimes called ‘curing’, but the use of the word ‘curing’ for onion drying is rather inaccurate since no cell regeneration or wound healing occurs as in other root crops such as yam and cassava. Drying reduces bulb weight and since they are sold mostly on a weight basis, achieving the desired level of dehydration is critical. Weight losses of 3-5% are normal under ambient drying conditions and up to 10 % with artificial drying. In traditional small-scale operations, onion drying is carried out in the field in a process commonly called ‘windrowing’. It involves harvesting the mature bulbs and laying them on their sides (in windrows) on the surface of the soil to dry for 1 or 2 weeks. In hot tropical climates, the bulbs storage should be in such a way to reduce the exposed surface to minimize damage due to direct exposure to the sun. In wet weather, the bulbs can take longer time to dry and may develop higher levels of rots during storage. The side of the bulb in contact with wet soil or moisture may also develop brown strains or pixels, which reduce the appearance quality and value.

After harvesting, expose onions to a mild temperature in a dry and ventilated area (curing).
Curing can also be done in warm shades for some time.
This process is important especially for long-term storage of onions.
During curing process, the skins dry into papery wrappers, the pungent compounds replace the sugars and the necks at the top of the bulbs come together sealing out moisture and microorganisms.
Dry the onions thoroughly before storage to avoid sprouting.

Onions should be stored in net bags, crates, in pallet boxes, or in bulk bins

c) Cleaning

Freedom from any impurity, which may materially alter the appearance or eating quality, is essential. Soil and other foreign materials must be removed and badly affected produce must be discarded. Cleaning may be carried out using air or by manually removing unwanted materials on the bulb surface. Care should be taken to avoid physical injury on the bulb during these operations.

Source: www.onehundreddollarsamonth.com

d) Storage

Before storing, bulbs should be properly dried and cured. Use some technique that will both remove surface moisture and allow high temperature formation of strong, intact outer protective skins and neck closure of the onion. High temperatures (e.g. 27° C or 80°F), low humidity (< 60% RH) and good ventilation are important in drying. Laying the onions on the soil in windrows is the simplest form of field drying. Alternatively, they may be removed from the field and placed in a heap, or spread in a shallow layer, preferably on a cement slab to avoid contamination of soil-borne pathogens. Problems associated with outdoor drying can include poor drying rates, sunscald, and rain.

A simple outdoor shaded structure can avoid these problems. A good design for natural ventilation is to make shallow trays with screen or woven bottoms. Arrange trays vertically, spaced sufficiently apart to catch the prevailing winds. If clear corrugated plastic sheeting is available, heat required for the curing process can be achieved by using it in the roof structure and thereby capturing passive solar energy.

Maintaining the bulbs at suitable temperature and humidity is vital to the successful storage of onions. The optimum relative humidity range is from 65-75%. There are two favorable temperature regimes. Minimal storage losses occur at 0-5°C (32-41° F), but for the farmer or villager not having refrigeration, 25-30°C (77-86° F) would be the best choice. Temperatures that are either too high or too low will increase rotting or sprouting. These are the greatest enemies to successful storage of onions. A high technology solution to the sprouting problem is to add chemical "sprout suppressants” prior to storage.

Onion Bags Sacks and nets used for onion packaging fall into three groups:

(i)general-purpose jute sacks, as used for many agricultural commodities, (ii) open-weave sacks of sisal-like fibre,

(ii)open-mesh nets, normally of plastic materials and

(iii)big bags, used alternatively to crates, containing up to 1000 kg . Jute sacks are readily available in most developing countries, but their disadvantages include: (i) generally too large - may contain 100 kg onions, hence difficult to handle and an increased risk of mechanical damage;

(iv)bulbs are not visible through the fabric, and it is difficult to monitor condition during storage;

(v)there is some resistance to airflow if they are used in an aerated store;

(vi)difficult to label effectively; and

Recycled sacks may encourage spread of postharvest diseases. Sisal sacks are made from sisal-like hard fibres and have an open weave, with thick threads spaced between about 10 and 15 cm apart. The rough nature of the fibre provides a sufficiently stable weave. These sacks are similar to jute sacks, but will allow limited visibility of the onions and impedance to airflow is less. Open-mesh nets are the most widely used package for onions, and they are normally red or orange in colour.

e) How to reduces Losses

The leaves and roots of the bulb should be trimmed off in order to remove soil in order to prevent the movement of pathogens into storage

Selection of good varieties.

Cautious use of nitrogenous fertilizers

Timely harvesting and proper curing of bulbs

Proper drying of leaves and shade curing

Fumigation and use of ventilated store

Large-scale onion storage

Source: theorganicfarmer.org

Onion stored in a net bag Ibitunguru

source: www.harrisseeds.com

15.Marketing

Most onion farmers sell their produce at farm gate especially in large-scale production. Farmers are not prone to huge losses because onions can be stored for a long period as long as they have been properly cured.