Sweet potato: Learn Uses, nursery, cultivation, manuring, harvesting, curing & storage

Introduction:

Sweet potato is annually growing perennial crop. It is believed to be originated from South America. Initially, its cultivation was popular only in Mexico, Mid & South America, West Indies. At present its cultivation is popular worldwide in tropical & temperate zones. It is mostly cultivated in Mid & South America, Mexico, Europe, India, China, Japan, Taiwan, South East Asia & Pacific islands.

In Nepal, it is cultivated as kitchen garden crop in Terai & Mid-Hills. It has not been cultivated as commercial crop in Nepal except some areas. It is highly nutritious crop however being under-utilized crop.

Uses:

Sweet potato is highly nutritious crop with abundant amount of Vitamin A, B, C & E along with Iron, plant fibers, Potassium etc. For a growing child daily feeding of 125 gram of red fleshy sweet potato supplies essential vitamin A amount. It is also widely used as chips, flour & baby foods. Starch content is used in paper & cosmetics industry. Its leaves are also edible with abundant nutrition. In Nepal, it is eaten during ‘Thula Ekadashi’ & ‘Maghe Sankranti’.

Cultivation technique:

Climate:

It requires warm & humid climate. It is extremely susceptible with frost & snow. Though it is tropical crop, it can be grown as rainy season crop in temperate climate with at least 5 months free from frost. It requires temperature above 24 degree Celsius for proper growth with complete growth check at below than 10 degree Celsius. Moderate rain with abundant sunlight helps in root growth. It can be grown upto an altitude of 1600m from sea level with annual rainfall greater than 750 mm.

Soil:

It can be grown in wide range of soils however, sandy loam or sandy soil with pH 5.6-6.6 is best suited. Deep soil with water logging condition is not appropriate for this crop. Irrigation facility with high productive soil is necessary.

Land preparation:

As this crop grows under soil, deep tillage for 2-3 times is beneficial for increasing production. Seed can be planted in plain or ridge of furrow with spacing of 60 cm * 30 cm (RR * PP).

Manuring:

Apply 10 tons well decomposed FYM at land preparation period with recommended dose of fertilizer 30: 30: 50 kg NPK/ha. It requires higher amount of potassium which suggest us to use ash in the field.

Propagation & Nursery:

It is propagated through vegetative propagation commonly. Some methods are:

  1. Runner`s cutting (Layering)
  2. Through buds of sweet potato
  3. Tuber

Two phases of nursery raising is essential for sweet potato. For 1 hector main field, 100 meters square first nursery is maintained with 100 kg of medium sized, weevil free root of sweet potato. It is set up before 3 months of main field transplantation. Apart from root, runner & buds can also be used. At spacing of 60 cm * 30 cm the roots are planted in first phase nursery. After 45-50 days runner develops & are ready for cutting & from that 20-30 cm long with 3 buds at least cutting is taken. They are planted in second phase nursery from where after 40-50 days they are ready for cuttings from where cuttings are again taken to plant in main field.

Planting season:

Terai: Falgun/Chaitra & Bhadra/Aswin

Forst winter areas: Planting to take Harvesting at Kartik/Mangsir

Seed rate:

Cuttings from 25-30 square meters nursery are planted in one ropani area. For one ropani, it requires 2700-2800 cuttings.

Irrigation & weeding:

Irrigate at 7-10 days interval for summer season crop whereas rainy season planting does not require irrigation. Drainage must be maintained well.

Weeding should be done once after 30 days after transplanting. After runner’s growth, weed is automatically checked.

Harvesting:

Leaves remain green upto when the climate is warm but in cold regions after the leaves turn yellow & start dropping, it is indication for harvesting. Crop becomes ready within 150-180 days. Avoid injury to root during uprooting.

Yield:

Orange sweet potato yields 20-40 ton/ha whereas local sweet potato yields only 5-10 tons/ha.

Curing:

Curing helps in treating wounds during uprooting & avoids rot & wrinkling problem during storage. Also, it helps in converting some starch into sugar to add more scent. Traditional curing involves heaping in field with sand covering from all sides for some weeks whereas modern commercial system involves storing root tubers at 75-80% Relative humidity, 27-30 degrees Celsius temperature warm, dark room for 10-14 days for curing.

Storage:

After curing, root tubers are stored at 13-16 degrees Celsius temperature with 75-80% RH dry & well aerated room. White fleshy sweet potato can be stored for 10 months. At low temperature it causes hard centre with low quality food whereas high temperature cause budding & wrinkling of root tubers.

Diseases:

Insects include sweet potato weevil, borer, beetle, aphid etc.

Disease include Root rot (Rhizoctonia sp/Pythium sp).

Insects:

Aphids:

  1. Spray Malathion @ 0.1% at 10-15 days interval to control the pest.

Red spider mite:

  1. Spray Malathion @ 0.1%.

Spotted beetle:

Spray Malathion @ 0.1% at 15 days interval.

Mealy bugs:

  1. Spray the crop with Malathion @ 0.05% at 15 days interval.
  2. Seed treatment of the tubers before planting.

Diseases:

Leaf blight:

  1. Use resistant/tolerant varieties.
  2. Use healthy planting materials and follow crop rotation.
  3. Spray Dithane M-45 @ 0.2% or Bordeaux mixture @ 1%.

Pythium rot:

  1. Follow sanitary methods.
  2. Select healthy and disease free planting materials.

Mosaic:

  1. Rogue out the diseases plants.
  2. Select healthy and disease free planting materials.

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