Potato is grown under temperate, subtropical and tropical conditions. It is essentially a “cool weather crop”, with temperature being the main limiting factor on production. Optimum temperature for germination, vegetative growth and tuber formation in potato is 25°C, 20°C and 16-24°C respectively. Tuber growth is sharply inhibited in temperatures below 10°C (50°F) and above 30°C (86°F); while optimum yields are obtained where mean daily temperatures are in the 18 to 20°C (64 to 68°F) range.
Red and white skin potato varieties are cultivated in the country. The white skin varieties are Santé, Multa, Diamant, Hermes, Lady Rosetta, Ajax and Patrones while the red skin varieties include Lala Faisal, Ultimas, Desiree, Cardinal, SH – 5, Kuroda, Oscar and Symphonia.
The potato can be grown almost on any type of soil except saline and alkaline soils. Naturally loose soils which offer the least resistance to enlargement of the tubers are preferred and loamy and sandy loam soils that are rich in organic matter with good drainage and aeration is most suitable. Soil with a pH range of 5.2-6.4 is considered ideal. To prevent the build-up of pathogens in the soil, farmers avoid growing potato on the same land from year to year. Instead they grow potato in rotations of three or more years, alternating with other dissimilar crops such as maize, beans and alfalfa.
Potato is propagated vegetatively. Well decomposed farm yard manure at 200-250 maunds per acre 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. Good water penetration and aeration is must for proper growth and tuber formation. Excessive tillage and land preparation causes compaction and should be avoided. To be effective the soil should be plowed below any compacted layer within the normal root zone and then disk harrowed before planting. Spike-tooth harrowing to break clods and level the soil may be needed just prior to planting.
For autumn and summer sowing potatoes complete potato is used. Potato tubers about one week before sowing are taken out from cold storage and spread at a cool and ventilated place usually under the shade of a tree. It starts bud development in 7-9 days and is sown when the sprouts are 1cm long. Potato seed remains dormant for 12 – 16 weeks so the tubers obtained from autumn crop and spring crop tubers is not used. 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 2 to 2.5 feet apart and the seed tubers are kept at 6 – 7 inches 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. There are several types of planters available that place the seeds in the soil and apply fertilizer and systemic insecticides in one operation. Seed depth should be about 4 inches below the top of the planted bed. Soil is ridged over the row by throwing soil to the plants during early cultivation, so that about 6 inches of soil cover the seed tuber when tuber formation occurs. For spring sowing potatoes 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. Sowing of sprouted seed is preferred which results in higher yields than the un-prouted ones.
Seed and Seed Rate
The seed contributes about 35-40% of the total cost of production in Pakistan. Formal certified seed production is limited and faces technical, economical and managerial problems. Lack of availability of sufficient quantities of good seed and low purchasing power of the farmers, forces them to rely on seed sources of doubtful quality or own production for which most of them do not have the proper skills. 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. Use only certified seed tubers. Seed required to plant an acre depends upon seed size and seed spacing. Potato seed tubers required 25 – 35 maunds per acre and it should be medium in size.
Potatoes are easy to grow, but they prefer cool weather so you should try to get them into the ground at the right time. 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% 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.
Before planting for the Punjab autumn crop, pre-irrigations may be required twice. The first one is required about 15 to 20 days before planting. It will allow annual weeds to germinate. Soil preparation should resume some 7 – 10 days after the first pre-irrigation. If there have been rains in this period and the soil is humid, this irrigation may not be required. The break in soil is still essential. The second pre-irrigation should be applied about 3 – 4 days before planting. Again this is only required if there are no rains during this time. It will help the germination of the tubers and reduce the risk of rotting, especially under hot weather conditions. Pre-irrigated soils help to achieve homogeneous germination.
Soil moisture is probably the most important factor determining potato yield and quality. About 15 – 20 inches of water is needed with center pivot irrigation system to produce a potato crop in Pakistan. When irrigation is practiced to supplement rainfall it should be applied in frequent light amounts. Secondary growth and growth cracks occur when irrigation or rainfall occurs after moisture stress. The soil should be kept uniformly moist until tubers have reached full size. For irrigation management decisions:
- The effective rooting depth of potatoes is two feet.
- The soil should not be allowed to dry below 65% of field capacity.
- Moisture levels above field capacity will seriously affect yield and quality.
On extremely sandy soils it is nearly impossible to prevent the soil from drying below 65% of field capacity due to the low water holding capacity. 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 by several intervals.
Well decomposed farm yard manure at 200 – 250 maunds per acre is recommended to be incorporated in the soil before land preparation Recommended NPK per acre is three bags of urea, 2 bags of DAP and one bag of SOP 50kg. All DAP & SOP is broadcasted at the time of 2nd pre-irrigation to easily dissolve in the soil. Urea is applied in different splits through fertigation system from 25 – 65 days after sowing. Contact between fertilizer and seed is avoided as it results in deterioration of seed tubers. Zinc sulphate 10kg bag 25% is also necessary to cure zinc deficiency.