ONION BULBS PRODUCTION TECHNOLOGY IN PAKISTAN

 

INTRODUCTION:

Vegetables are an integral part of the cropping pattern but occupy only 2 % of the total cultivated area of Pakistan. Almost 50 kinds of vegetables, onion being one of them, are grown in the country. Onion, Allium cepa L., a bulb, is a member of the family Alliaceae, originated from Central Asia i.e. Afghanistan, Tajikistan and Uzbekistan. Most of the wild species were found in Central Asia.

Onion occupies an important place in vegetable culture here in Pakistan. It is grown throughout the year in the entire country and used as a vegetable and condiment in almost every savoury dish of the family menu. Onion being pungent in nature is an essential item of the Asian kitchen, which is due to the presence of a volatile oil, allylpropyl disulfide and numerous other sulfur-containing compounds.

            Freshly harvested onions bulbs.

In Pakistan, onions can be grown at locations from sea level to snow line. However,  adoption of improved cultural practices and crop management are the prerequisites for getting higher yields with comparatively low production costs. This is possible only with prior planning based on a sound footing, which includes the use of high quality seed with a known source ensuring genetic purity, proper time of planting, soil preparation, use of balanced fertilizer doses at a reasonably suitable time in line with the recommendations of experts, based on soil testing, which is the first leg of planning. On the second leg, the cultural practices, inhibition of weed competition with the crop, pest and disease scouting and control prior to their inflicting damage on the crop, and judging the maturity index before harvesting are required. All these steps are of utmost importance for having an economically worth-while production of onions. However, the package of production technology for growing onion bulbs is below:

SOIL AND LAND PREPARATION:

Onion crop can be grown on almost all types of soils with a pH range of 5.5 to 7.5. However, the idle soil is sandy loam, which is preferred for early crop. Higher yields can be obtained from well-drained loamy, clay-loam, silt loam soils containing adequate organic matter. Poorly drained heavy soils are not suitable for onion cultivation.

Ploughing must be avoided when the soil is too wet, otherwise large clods will be formed in heavier soil. Plough the soil when it is in proper moisture conditions. A simple test to know the moisture condition is that the soil should be pressed in hand, if it crumbles, it is fit to plough. But if it retains the form, the land is too wet. The land should be ploughed 3-4 times. Planking should follow the ploughing. At the time of planting, the soil should be firm. 

SEED RATE:

Seed rate depends upon inter and intra-row spacing in the field for any crop. Seed and varietal choice is the first step in the production planing of a crop. If it is of good quality and true to type, half of the battle of getting higher yield is won. Special care must be exercised in selecting variety and seed. About 5.00 Kgs. seed is enough to plant one hectare land. 

TIME AND METHOD OF SOWING:

Techniques for nursery raising:

For bulb production, seed is sown in the month of October on raised nursery bed, which is 12-15 cm high and 1 meter wide. Clods, pebbles and extra material are removed from soil bed. The bed is then leveled so that extra irrigation and rainfall water automatically runs-off. Seed is planted on lines, which are 2-3 cm deep and 3-4 cm apart. The seed is planted and bed is covered with well rotten farm yard manure. Immediately after this practice, the bed is irrigated with sprinkler either in morning or evening. If the weather is hot, it should be irrigated twice a day. A seed rate of 5 kg is used for raising bulbs for one hectare of land.

Before transplantation, the nursery should be hardened for 7-10 days with halting irrigation. Prior to eradication of the seedlings, the nursery should be irrigated to make the process of uprooting easy. In this way, the danger of breakage of seedling is minimized.

 Transplantation:

As the nursery get 3-4 leaves, seedlings transplantation is done from the end of November, and this goes on till the beginning of January, using firmed flat beds. Row to row distance is kept 20 cm and plant to plant 10 cm. Before the transplantation, the recommended dose of fertilizers is applied.

 FERTILIZER REQUIREMENTS:

Farm Yard   and green manures are suitable for improving soil structure, water holding capacity and increasing aeration. Well rotten and dry animal manure should be applied at the rate of 8-12 ton per acre during land preparation in order to get high yield.

Green manuring is also a good source of adding nutrition to the field. A suitable crop ( should be planted when the fields remains fallow for some time. It should be ploughed and well mixed in the field before flowers initiation. 

Generally, the application of balanced fertilizers plays a vital role in getting higher yields for almost every crop. Fertilizers are broadcast prior to sowing and mixed in soil through ploughing ploughing. Onion crop is highly responsive to fertilizers. During the experimentation, application of NPK fertilizers @ 180:150:140 Kgs/ ha has increased the marketable yield. For better results, full quantity of phosphorous and potash and half quantity of nitrogen should be applied prior to sowing. The remaining half dose of urea should be applied with first weeding and hoeing. 

 IRRIGARTION:

It is not possible to grow onion crop without irrigation. The crop on sandy soil should be irrigated after 10 days in winter season and in hot weather, after 7 days. Over irrigation must be avoided as it helps spreading the disease in the crop.

  WEEDING AND HOEING:

Weeds, as old as the evolution of crops, have evolved parallel with the latter. Weeds are excellently adapted to the prevailing environment and divert energy from a direction desired by man. Weed control is vital to producing high quality onions as the crop competes poorly with weeds, which can drastically reduce yield and quality. Weeds competition reduces the amount of water, nutrients, light onion receives and provide opportunity to insects and diseases to breed and groom in it, which attack the crop. Traditionally weed control is done manually as well as through chemicals (weedicide). However, chemical weed control has taken momentum in the recent past. But, the timing and method of application of the spray is of paramount importance. The best time of application is just after transplanting from the nursery into the pre-prepared field. Either the crop is sprayed with herbicide and irrigated immediately or the field is irrigated after transplantation and then sprayed after three days when the field is still wet. Both methods of application give good control and the field remains free of weeds for about 50-60 days. After that one hoeing is done and the remaining nitrogen is applied. Many brands of weedicides are used. But best results are achieved with the use of Stomp or Pendimethalin at the rate of 2 ml/litre of water.

 PEST CONTROL:

DISEASES:   

Generally the onion crop faces many hazards in Pakistan. Among them, downy mildew, purple blotch, botrytis, smut and grey mould diseases  are the most damaging ones, as it inflict severe losses on the crop and consequently on the farmers in terms of money. The most serious prevailing diseases are discussed below.  

Downy mildew:

The technical name of downy mildew is Peronospora destructor, which is a Phycomycete belonging to class Oomycetes. It is an established fact that this disease lowers the quality and quantity of plant or plant products in the field by destroying the leaf tissues and allowing entry to other pathogens. The downy mildew, causing 60-75% reduction in bulb yield, is one of the most serious disease of onion in many parts of the world, including Pakistan. The fungus of the disease (Peronospora destructor (Berk.) Casp.) over-winters as systemic mycelium in bulbs and as oospores on the surface of seed and in soil. The incidence of the disease can be reduced substantially with effective use of various management practices. In this regards, systemic fungicides; Aliatte @ 1.5 gram or Ridomil @ 2.0 gram /litre of water are recommended. 

Purple blotch:

The technical name of purple blotch is Alternaria porri, which belongs to the order Moniliales. This disease mostly attacks the onion seed crop in areas which receive high rainfall, in the wake of which humidity increases, which favours the disease. In severe cases, 100 % damage to seed crop occurs, resulting in total loss.

The disease affects bulbs, seed stalks and leaves. While the fungus is a wide-spread one, it is most serious in irrigated areas. The symptoms are small, white, sunken lesions with purple centres, which rapidly enlarge and eventually girdle the leaf or seed stem. Penetration is through stomata and wounds. Purple blotch is commonly associated with downy mildew, but the former develops over a much wider geographical range and has less exacting climatic requirements for development.

Purple blotch has now become a menace and causes severe losses. Crop management techniques coupled with regular sprays of fungicides with the recommendations of the experts should be adopted, once the symptoms of the disease appear. In this regards, systemic fungicides; Aliatte @ 1.5 gram or Ridomil @ 2.0 gram /litre of water are recommended. However, indiscriminate sprays with no proper schedule may have either no or little effect on the crop. Usually the farmers spray their crop on the recommendations of the pesticide dealers/shopkeepers, which leaves them at the mercy of the circumstances. This practice should seriously be avoided.

INSECTS:

A wide range of insects  attacks the onion crop in the field. A few of them cause severe damage to the crop, which not only reduce the yield, but affects the quality as well. Among them budworm (Heliothis spp.), thrips and maggots are very common. Most of the research work carried out on these insects is only based on chemical (insecticide) control in Pakistan. However, the damage caused by these insects has not been assessed in terms of yield or economics in the country.

Thrips:

The technical name of thrips is Thrips tabaci. Describing the way of thrips damages the onion crop, that most thysanoptera (Order) feed by penetrating the living tissues of plants with their piercing mouth parts and imbibing the sap. Among them, the most widely distributed pests on onions are Thrips tabaci, which damage the leaves on which they feed.  Various insecticides like carborufan, cypermethrin, deltamethrin + triazophos and dimethoate have been evaluated, which reduced the population of thrips for more than two weeks.

Budworm:

Budworm (Heliothis spp.) attacks the umbels of onion plant at the seed formation stage, which damages the crop severely and  reduces the seed yield drastically. In early stages if it attacks  the inflorescence, eating the flower buds, then seed formation does not take place and if in later stages it damages the capsules, then the seed does not  mature. The damage can clearly be seen in the field. It has been observed that almost all species of Heliothis attack the onion seed crop inflicting severe damage on it. A wide range of the products are available in the market to control this insect. Among them, Larsban, Timaron and Karate (each 2.5 ml/litre of water) are the most effective products. 

 Maggot:

Since a year, maggot (onion fly) has been identified for the first time in Pakistan, which is an addition to the list of insects that attack and cause severe damage to onions, both seed and bulb crops. The intensity of the attack is usually higher in the areas where a rice-onion based cropping pattern is practiced. Maggots attack the completely established young plants at the root zone at about 30-40 days after transplanting. As the infestation progresses the plant shows symptoms which resemble root rot. The plant growth remains stunted and the leaves and stalks turn yellow. The maggots are clearly seen feeding on roots when the plant is pulled up.  Subsequently,  the bulb gets soft and exudes a brown liquid.  Looking to the current situation, this insect could soon take on the status of an economic pest and inflict considerable losses on the commercial crop. 

 HARVESTING, CURING, PACKING AND PACKING MATERIAL:

Onions are harvested when 60-70 % neck down of the tops occurs. However, in principle the entire leaves should be dried. Before harvesting, irrigation should be stopped to dry out the crop completely for maximizing the quality of storability. The tops are cut 2-3 cm above the neck of the bulb after harvesting the crop to minimize the chance of disease penetration during storage. After harvesting, the process of curing gets started, which means the duration of the gradual bulb skin drying process after harvesting.  During curing, the bulbs are drying and packing for market or store in which the field heat and excessive moisture from the bulbs are reduced in the presence of sunlight and air. In this process, the stalks are cut and the bulbs are sorted out. The cut, bruised, diseased, rotted and damaged bulbs are removed. The good quality bulbs are piled up under temporary sheds or partially covered with grasses to avoid sunscald. The length of time required for curing depends largely on the local weather conditions. Thorough curing requires 10-15 days for completion of the process. In southern parts of the country (Balochistan province), this process takes a  longer period, i.e. a month.

Although the curing is known by experience to directly impact bulb storability, there is a  lack of  evidence in the form of experimental data on this stage. . Researchers need  to revisit this phenomenon with systematic research work and  come up with crystal clear findings and recommendations for length of time of curing.      

In Pakistan, after curing, the onions are packed in gunny bags. Usually 50 kgs and 75 kgs bulbs are packed in a bag. The top of the bag is loosely knitted closed with nylon wire. Good quality bulbs of large size are put on the top of the bag to give a good impression during the auction in the market for attracting buyers.  Little or no grading carried out and onions of mixed sizes are packed within the bag. The secondary wholesalers and retailers grade the onions prior to sale.  They know very well what sizes of onions are required for different markets such as the Gulf States, Malaysia and Sri Lanka.  Some markets actually prefer small sized onions.