A STORY OF POTATO
DR. S. M.ALAM & M.A.KHAN
May 18 - 24, 2009
Potato is the term which applies either to the starchy tuberous crop from the perennial plant Solanum tuberosum of the Solanaceae family. Potato is the world's most widely grown tuber crop, and the fourth largest food crop in terms of fresh produce ó after rice, wheat, and maize (corn). The potato originated in the area of contemporary Peru and Bolivia, identified more specifically in research published by David Spooner in 2005 as an area of southern Peru, just north of Lake Titicaca.
According to FAO, the global output of potato was 345 million tons in 2007 with China providing the highest yield followed by Russia and India.
Potato is tasty, nutritive, and highly digestible vegetable with 75% 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 fiber. 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 is free of cholesterol and also contains some antioxidants which are capable of protecting human beings against cancer and heart diseases. Potato mask can be employed for skin beauty especially on the pigmented ones.
Potato is extensively cultivated all over Pakistan. 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% more than the preceding year's production of 1.5 million tons. Punjab, NWFP, Sindh and Baluchistan contribute 83,9,1, and 7 per cent respectively to the total potato production.
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 fertilizer and irrigation, and damages caused to potato tubers during harvesting, packing, transport and storage. Potato can be grown from sea level to 3,000 m altitude. The major potato growing districts in Pakistan are Kalat, Pishin and Killa in Baluchistan; 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% 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% 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, Diamante, Ajax and Patrons 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 tractor drawn ridges 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.
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 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. Weeds are serious threat to potato crop and may cause 20-30 per cent losses of the crop. 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 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.