Production Methods/onion

The Most Distinct Methods of Planting Onions Include
 Sowing seed directly in the field where the crop is to mature
 Sowing in a seedbed from which the plants are transplanted later to the field and
 Planting sets. A grower may buy these sets, or grow them from seed himself. The transplanting method is used more commonly for early production.
Autumn Crop
Onion is grown throughout Pakistan in varying volumes and with different harvesting seasons. However, supply of onion falls in short of requirements from December-January and prices soars to more than five times compared with normal season. The nursery for off-season / autumn crop of onion is raised in first week of July and the seedlings are transplanted in the field in the middle of August for harvesting of bulbs during December. It is difficult to manage nursery seedlings of autumn crop because of high temperature and monsoon rains.

Sometimes, the heavy rains cause severe damage to nursery seedlings. This difficulty can be overcome through direct planting of onion sets and to eliminate the step of nursery raising which is not only time consuming but laborious as well. All varieties of onion are not suitable for autumn crop. Furthermore, size of onion set is closely related to subsequent bulb yield. During 1999-2005, work on off-season/ autumn crop of onion production through sets was conducted at NARC. Phulkara variety of onion was found most suitable for autumn season cultivation. Set size in the range of 17-21 mm diameter produced the highest marketable bulb yield of onion.
Soil
Onion can be grown on a wide range of soils preferably sandy rich loam, well drained containing sufficient organic material to retain soil moisture for proper growth. Soil with pH from 6 to 7 is suitable for optimum crop growth. Hard soils induce the bulbs to be small and irregular in shape. Adequate quantity of manure and fertilizer is necessary for successful onion production.

Land Preparation
Proper land preparation is very important to ensure a uniform stand and higher onion bulb yield which can be achieved following below mentioned practices. Deep-turn soil at least three to four weeks prior to planting, using a moldboard plough. The soil should be ploughed to depth of 15 to 20 cm and one or two planking are sufficient to get good tilth and leveled seedbed. Rough and lumpy ground is not suited to the planting of onion seeds/seedlings/sets. Land must be leveled in order to irrigate the plants properly. Although onion has limited root system but is very responsive to manures and commercial fertilizers. Well-rotten farmyard manure @ 10 tonnes per acre should be ploughed down at the time of land preparation at least one month before land preparation. Before transplanting 3 bags of super phosphate, one bag of ammonium sulphate and one bag of potassium sulphate per acre should be thoroughly mixed in the soil.
Spacing
Onions are usually transplanted in the field at 10 cm plant-to-plant spacing and 25-30 cm apart in rows on flat beds from mid August to 1st week of September. Space the plants 10 cm apart in the row to produce large-sized bulbs (closer spacing significantly decreases bulb size). Keep onions free from weeds by shallow cultivation and hoeing.
Fertilization
A supplementary dose of one bag of ammonium sulphate per acre should be applied one month after planting. Another dose of one bag of ammonium sulphate may be applied at the time of bulb formation. Generally excess of nitrogen causes onion bulbs to become less firm. Similarly, late application of nitrogen as top-dressing should be avoided, as it causes thick-necked bulbs. A good combination of potash and phosphate promotes firmness of bulbs and regular ripening.
Irrigation
The onion has a shallow root system, with most of its roots in the top 12 inches of soil. An onion continues to produce new roots (three or four per week) throughout the entire growing season as older roots die. Root growth is most active during early plant growth. Proper soil moisture is critical for continuous root growth and for supplying the needs of the foliage and bulb. Make sure good soil moisture exists before and after seeding, transplanting or setting sets. Prior to emergence and during the first three weeks of seedling growth, it is essential that adequate moisture be maintained in the top three to four inches of the soil. The first irrigation is given immediately after sowing and transplanting. Thereafter, onions are usually irrigated after ten days interval which can be increased or decreased according to climatic conditions. Irrigation must be discontinued before neck fall, to allow the bulbs to ripen off. Over-watering just before harvest can increase disease, splits and doubles.

Hoeing and Weeding
Weeds and grass compete with the onion plants for nutrients and moisture during the growing season. Onions have shallow roots and compete poorly with weeds and grasses. Timely shallow hoeing and cultivation are important, especially when the onions are small. Onion plant grows slowly during early growth stages therefore, fast growing weeds affect crop very badly. It is essential that weeds must be kept under control to produce a good crop of onion. Onions should be hoed lightly, as it is a shallow rooted crop. Generally three to four hoeing are sufficient to control weeds.
Yield
The yield of onion crop in Pakistan is still lower as compared to others countries. One of the reasons for low yield could be low yield potential of existing cultivars. No doubt the use of improved agricultural practices may increase the yield of crop but genetically superior genotypes play a remarkable role in increasing the yield of onion crop.
Harvesting
Practices in onion harvesting include undercutting the onions, allowing them to cure (air dry) for two to three days, clipping the tops and roots, bagging in sacks, transporting to the grading shed and marketing. Remove any plants that have formed flower stalks. They do not produce good bulbs for dry storage. Harvest when most of the tops have fallen over. Keep the dry wrapper scales as intact as possible on the bulbs, as they enhance the keeping ability. Onions should be harvested when 50 to 70 percent of the tops have fallen over.

Curing
The only post-harvest treatment required for the long storage of bulb onions is a thorough curing of the bulbs. The curing of dry bulb onions, carried out immediately after harvest, is a drying-out process. Onions are considered cured when neck is tight and the outer scales are dried until they rustle. The length of curing depends on temperature, humidity, wind or air movement and neck moisture at topping. If the onions are mature, humidity low and air movement good, couple of days may be sufficient. Under dry, warm conditions onions are left in the field for a few days until the green tops, outer skins and roots are fully dried. Under wet conditions, it may be necessary to dry onions on racks or trays under cover. The essentials of curing are heat and good ventilation, preferably with low humidity. It dries out the neck and the two or three outer layers of the bulb. The outermost layer, which may be contaminated with soil, usually falls away easily when the bulbs are cured exposing the dry under-layer, which should have an attractive appearance. If onions cannot be dried in the field, they can be staked in a warm, covered area with good ventilation.

After the bulbs dry, cut the tops 2 cm long (at or above the narrow spot where the stem bent over) and place the bulb in dry storage with good air circulation. The roots are trimmed close to the stem or base. The bulbs that are bruised, cut or diseased, or those with green tops or thick necks should not be stored. The roots are trimmed close to the stem or base. Cultivars with more dry matter content tend to be long storing types. The dry matter content of bulbs differs greatly between cultivars, ranging from 6 to 8 percent of fresh weight. Generally, pungent varieties of onion perform much better than mild varieties during storage. Onions should not be allowed to get damp; otherwise, they tend to start growth again.
Storage/Marketing
Sort and inspect onions immediately following curing, before shipping or storing. If the onions are left unattended for more than one week, inspect them again, since diseased onions are likely to infect other onions during shipping or storage. Fresh market onions should be in the hands of the consumer within four weeks of harvest.

Quality Standards and Grades
Quality is the most important factor when producing a marketable product. The onions must be free from rotting or deterioration to make it unfit for consumption and should be clean, practically free of any visible foreign matter. The outer skin of the onion must be fully dried. Bulbs should be without hollow or tough stems and free from damage caused by pests. In addition the stems must be twisted or clean cut and must not exceed 3 cm in length. Onions must be of good quality. They must be characteristic of the variety. The bulbs must be firm, compact, un-sprouted (free from externally visible shoots), free from swelling caused by abnormal development and practically free of root tufts. Size is determined by the maximum diameter of the equatorial section. Onion bulbs are graded in four sizes namely, large (64 mm and above), medium (51-64 mm), small (38-51 mm) and general (24-38 mm).

Packaging
Onions may be presented in appropriate packages. These may include polypropylene net bags, jute sacks or other such packages specified in the sale contract and allowed in the country of import. Onions are commonly packed in mesh bags containing 15, or 25 kg of bulbs. They should be transported and stored separately from other kinds of produce. Many types of fruits and vegetables will readily absorb the odor of onions. Well-dried onions also draw moisture readily from fresh vegetables. Green onions are normally tied in bunches by the growers. The contents of each package must be uniform and contain only onions of the same origin, variety, quality and size.
Phyto-sanitary Certification
The phyto-sanitary certificate is a prerequisite. It is issued by the National Plant Quarantine Department to the effect that the produce is fit for human consumption. It will neither pose any health risk to human beings nor will transmit any insect pest or disease to the importing country.
Development Strategy
There is a need to improve farm management practices leading to better quality and more yields. New cultivars should be introduced based on targeted import markets requirements and their suitability for processing like dehydration. Pack-houses with grading & packing facilities should be developed at farm level. The processing industries should introduce value added products such as onion flakes, onion powder and fried onion in the market. Seminars should be conducted to create awareness on Good Agriculture Practices (GAP).
Insects and Diseases of Onion
Insects
Onion Thrips
Onion thrips (Thrips tabaci) are small, yellowish sucking insects, which feed on the foliage of onion plants. Thrips are most injurious during dry weather. Spraying with appropriate insecticide at weekly interval on the plants has given excellent control.
Diseases
Downy Mildew
The downy mildew of onion (Peronospora destructor) is a fungal disease of onion grown in cool moist conditions. In humid weather, fungus develops as white or purplish downy growth over the leaf surface but in dry weather, only white spots are seen. Dithane M-45 or any other copper based fungicide can be used to control the disease.
Purple Blotch
Purple blotch (Alternaria porri) is a serious fungal disease of onion that occurs at temperature range of 25-30 0C with 70-90 percent relative humidity. The leaves and flower stalks show whitish flecks with purple colour centre, which on further development form dead patches. Spray the crop with Dithane M-45 at fortnightly interval before appearance of the disease. Keep the crop free from the weeds.
The Color of Onions
Bulb onions can be yellow, red, or white. Approximately 87 percent of the crop is devoted to yellow onion production, with about eight percent red onions, and five percent white onions.
Yellow Onion

Yellow Onions are full-flavored and are a reliable standby for cooking almost anything. Yellow onions turn a rich, dark brown when cooked and give French Onion Soup its tangy sweet flavor.
Red Onion

Red Onions, with their wonderful color, are a good choice for lots of fresh uses or for grilling, charbroiling, and roasting.

White Onion

White Onions are often used in prepared salads, white sauces, and is the traditional onion for classic Mexican cuisine. They have a golden color and sweet flavor when sauteed.

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