Rising potato production and export potential
By Khawar Jabran and Dr Ehsan Ullah
POTATO is a tasty, nutritive and highly digestible vegetable with 75 per cent water contents. One hundred grams of potato possesses 22g carbohydrate, two gram protein, 90 kilocalories energy, 13mg calcium, 17mg vitamin C, 11mg riboflavin 1.2 mg niacin and traces of certain other minerals and fibre.
Potato is eaten intensively in a variety of forms such as boiled, baked, and cooked. As vegetable it is eaten alone as well as mixed with other vegetables, and as snacks, the most popular of them being the finger chips. It has medical significance.
It is free of cholesterol and also contains some antioxidants which are capable of protecting human beings against cancer and heart diseases.
It has potential to lower high blood pressures due to presence of a compound kukoamine. Potato mask can be employed for skin beauty especially on the pigmented ones.
Potato tubers if exposed to sunlight during growth become green in colour due to formation of poisonous alkaloid compounds solanine and chaconin which are injurious for humans as well as animals and can even cause death.
Potato was introduced to the subcontinent in the 16th century and at present it is being grown as cash crop.
During the year 2006-07 the area under potato was 0.131 million hectares (ha) with a total production of 2.6 million tons which was 67.2 per cent more than the preceding years production of 1.5 million tons.
Punjab, NWFP, Sindh and Balochistan contribute 83, nine, one, and seven per cent respectively to the total potato production.
Average price of potato in the country increased from approximately Rs250 per 40kg in 2000-01 to Rs550 per 40kg in 2005-06. Exports of potato either chilled or fresh during the year 2005-06 were 15.39 million kg earning a foreign exchange worth Rs173.2 million which was lower than the previous years export of 20.76 million kg earning a foreign exchange equal to Rs183.99 million. Sri Lanka, Afghanistan and Malaysia are the major markets of Pakistani potato.
Although there was considerable increase over the time in area and production of the crop in the country, however, the average yield is still lower than the potential.
Various factors accountable for low potato yields include lack of knowledge among farmers about growing techniques, costly seed, diseases, weeds and insect pests, mismanagement of fertiliser and irrigation, and damages caused to potato tubers during harvesting, packing, transport and storage.
Potato can be grown from sea level to 3,000m altitude. The major potato growing districts in Pakistan are Kalat, Pishin and Killa in Balochistan; Sialkot, Okara, Sahiwal, Jhang, Kasur and Gujranwala in Punjab; and Dir, Nowshehra and Mansehra in NWFP.
Three potato crops can be grown in the country in one year, two in plains including autumn and spring and one in hilly areas during the summer season.
The time for plantation of autumn crop, which contributes more than 70 per cent of the total yield, starts in early October and ends in mid November.
Spring crop contributing less than 10 per cent to the total yield, can be sown from mid- December to mid -February while the summer crop contributing more than 15 per cent is sown in early April up to mid- May.
Red and white skin potato varieties are cultivated in the country. The white skin varieties are Sante, Multa, Diamant, Ajax and Patrones while the red skin varieties include Lala Faisal, Ultimas, Desiree, Cardinal, Oscar and Symphonia.
Deep, fertile, well-drained, well-aerated, loose-textured, sandy loam, silt loam and peat soils with a neutral pH are best suited for potato cultivation.
Optimum temperature for germination, vegetative growth and tuber formation in potato is 25°C, 20°C and 16-24°C respectively.
Well decomposed farm yard manure at 20-25 tons per ha is recommended to be incorporated in the soil before land preparation. Field is given a soaking irrigation nearly two weeks before sowing to provide seed tubers with ample moisture for germination.
Field is ploughed 3-4 times using a mould board plough followed by two harrowing to prepare a fine seedbed.
Potato is propagated vegetatively. For acquiring optimal potato yield certified, healthy, vigorous and disease-free seed tubers are indispensable. Seed tubers must be of uniform size and shape without any sign of infection.
One potato tuber can be cut into pieces before sowing but the weight of each piece must be nearly 50g possessing 2-3 eyes. However, the cut pieces are more vulnerable to diseases.
Seed rate is variable depending on the size of the tubers, however 800-1000kg potato tubers are recommended for cultivation of one hectare. Sowing of sprouted seed is preferred which results in higher yields than the un-sprouted ones.
Potato tubers about one week before sowing are taken out of cold storage and spread at a cool and ventilated place usually under the shade of a tree. They start germinating in 7-9 days and are sown when the sprouts are 1cm long.
Potato seed remains dormant for 12-16 weeks so the tubers obtained from autumn crop can not be used to plant spring crop. Seed tubers are treated with fungicides like dithane-M, captan or benlate to protect them from fungal infections.
Potato tubers can be planted either on flat beds, in the furrows or on the ridges; however, ridge sowing is the most preferred method.
Ridges are 30cm high and 60cm wide. Ridges are marked at 60-75cm apart and the seed tubers are kept at 15-20cm distance and at the end the ridges are made using a tractor drawn ridger to cover the seed with soil.
Potato accomplishes its growth very speedily and has high nutrient requirements.
Recommended NPK per ha is 175kg, 125kg and 125kg respectively. All P, K and half N are added at the time of sowing as band placement along with the seed tubers while the remaining N is given 30-40 days after sowing.
Contact between the fertiliser and seed is avoided as it results in deterioration of seed tubers. Zinc sulphate 25 per cent is added at 25kg per ha to cure zinc deficiency.
Potato is irrigated 5-7 days after planting or even earlier and the subsequent irrigations are applied depending on the soil, crop and environmental conditions usually with 7-10 days interval.
Over irrigation causes the water to reach the top of ridges to harden the soil surface and resultantly impede soil aeration, so care must be taken to keep water below the apex.
Severe damages caused to potato crop due to frost in the month of December can be evaded by irrigating the fields.
More or less 15 fungal, bacterial and viral diseases are known to harm potato crop.
Major fungal diseases of potato include early and late blight, wilts, powdery scab, common scab and black scurf while leaf roll, virus Y and mycoplasma are the common viral diseases of potato.
Potato cyst and root knot are caused by nematodes while black leg and hollow heart common bacterial diseases.
Disease management in potato include sowing of healthy, disease free seed, destroying plant debris after harvesting, cultivating crop on well drained soils and raised beds or ridges, controlling insects, proper crop rotation and rouging of infected plants.
Most of fungal diseases can be controlled or at least prevented by following the above mentioned practices along with application of fungicides like dithane-M, benlate and bordeaux mixture.
Aphids, jassids, leaf hoppers, and the cut worms are most damaging insects of potato. Aphid also acts as vector for spread of viral diseases.
Neem extract two per cent solution is effective to control aphids and jassids in potato crop. Cutworms incise young potato plants at ground level and feed on tubers.
They get suppressed by flooding of the field. Moreover, application of carbafuron 3G at 25kg per ha control cutworms and leaf hoppers in potato.
Weeds are serious threat to potato crop and may cause 20-30 per cent losses of the crop. Pre-emergence application of either of the herbicides pendimethalin 330E, gramaxone 20EC or sencor 70WP at 2.25L, 3.0L, 750g per ha respectively, effectively control potato weeds.
Potato crop matures in 100-120 days. Drying of vines, hardening of potato skin and yellowing of leaves are the indications that the tubers have gained maximum size and weight.
Potatoes are reaped either using a mechanical harvester or manually using spade for their digging.
Tubers if kept under shade for 2-3 days harden their skin to avoid its removal during grading and packaging. Tubers are graded for separate packaging of superior grade to get high prices.
Potato tubers which are uninjured, clean, dry and free from diseases are packed in clean, disinfected and unspoiled bags. Potatoes to be kept for seed purposes are stored at 3-4°C while the ones to be marketed after 2-3 months can be stored at 10-15°C.
Rising potato production and export potential -DAWN - Business; December 10, 2007
