Onion cultivation and marketing: A Pakistan Issue

Districts where onion is mainly produced in Punjab are Khanewal, Vehari, Okara, D. G. Khan, Bahawalpur and R. Y. Khan d. Ghotki, Nausherhro Feroze, Nawabshah, Shikarpur, Sanghar, Mirpur Khas and Hyderabad are main onion producing district in Sindh. Similarly Swat and Dir in KPK and Mastung, Kalat and Chagai are main onion producing districts in Baluchistan.

When the day length is of the proper duration onions starts bulb formation. Different varieties of onions require different day lengths to initiate bulbing. Generally most common varieties fall into one of two classes, long-day and short-day. For this reason, onion varieties that are grown in the South are not adaptable to the North and vice versa.

The agro-ecological diversity obtained in the country enables production of onions almost around the year. However, production volumes greatly differ from crop to crop as follows:

• ·        Punjab & Khyber Pakhtoon Khawa Plains (June-July )  = 13%
• ·        Khyber Pakhtoon Khawa Uplands (August-September) = 16%
• ·        Baluchistan (August-October) = 26%
• ·        Sindh (November-May) = 45%

From the above information, it appears that bulk of the onion crop is harvested from August to May. The augmented supplies tend to keep prices in the domestic market low thereby offering an opportunity for export. Therefore, onion exports are mainly undertaken during this period, predominantly from Sindh crop. Due to limited shelf life and absence of suitable cold storage facilities in the country, onion is disposed in the domestic and international market as fresh harvest. 

Following issues need to be addressed in this regard:

• Identification of suitable varieties for short to intermediate days, high yield with better storage quality.
• Inadequate supply of good quality seed
• Hoeing and weeding for control of weeds in onion crop is very expensive.
• Considerable damage is done to onion crop by thrips, purple blotch and downy mildew.
• Phosphorus and potash fertilizers are rarely used by the farmers. As a result the bulbs have very poor storage quality.
• Marketing of surplus produce of onion during the year of over production is a great problem.

As onion is a cool season plant, its optimum temperature for seed germination ranges from 20-25 °C, early growth stages before bulbing require 13°C to 20°C and bulb development needs 16°C to 25°C. Best growth and quality is obtained when the temperature is cool during the early development and warm near maturity. A dry atmosphere at harvest is desirable to obtain satisfactory curing of the bulbs. The onion is fairly resistant to frost injury, but not unaffected. At low temperature, bulbing takes place very slowly and if the temperature is very low, no bulbing takes place. At low temperature onions are more inclined to run to seed called bolting.

The most distinct methods of planting onions include.

1.      Sowing seed directly in the field where the crop is to mature.

2.     Sowing in a seedbed from which the plants are transplanted later to the field.

3.      Planting sets. 

A grower may buy these sets, or grow them from seed himself. The transplanting method is used more commonly for early production.

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. Heavy rains may 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.

Onion can be grown on a wide range of soils preferably sandy rich loam, if it is 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.

Appropriate land preparation is very important to ensure a uniform stand and higher onion bulb yield which can be achieved following some practices.

1.      Deep-turn soil at least three to four weeks, prior to planting, using a moldboard plough.

2.     The soil should be ploughed to depth of 15 cm to 20 cm and one or two planking are sufficient to get good tilth and leveled seedbed.

3.      Rough and lumpy ground is not suited to the planting of onion seeds/seedlings/sets.

4.      Land must be leveled in order to irrigate the plants properly.

5.    Although onion has limited root system but is very responsive to manures and commercial fertilizers. Well-rotten farmyard manure @ 10 tons per acre should be ploughed down at the time of land preparation at least one month before land preparation.

6.     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.

Transplantation of onions in the field is done at 10 cm plant-to-plant spacing and 25-30 cm apart in rows on flat beds from mid August to 1^st week of September. the plants should be spaced 10 cm apart in the row to produce large-sized bulbs (closer spacing considerably decreases bulb size). Onions should be kept free from weeds by shallow cultivation and hoeing.

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, because it causes thick-necked bulbs. A good combination of potash and phosphate promotes firmness of bulbs and regular ripening.

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 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.

Onions have shallow roots and compete poorly with weeds and grasses. Weeds and grass compete with the onion plants for nutrients and moisture during the growing season. 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.

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.

Onions should be harvested when 50 to 70 percent of the tops have fallen over. Practices in onion harvesting include undercutting the onions, allowing them to cure 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.

The curing of dry bulb onions, carried out immediately after harvest, is a drying-out process. The only post-harvest treatment required for the long storage of bulb onions is a thorough curing of the bulbs. 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  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. 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 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 3cm 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 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).

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 certificate is a pre-requisite. 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.

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.