Sweet Potato Cultivation Guide: Shakarkand Farming and Yield

Sweet potato, locally known as Shakarkand in India, is a highly resilient and nutritious root crop that holds significant commercial value. It is grown widely across different agro-climatic zones, from the tropical southern plains to the northern sub-temperate tracts. As a crop that requires relatively low inputs compared to traditional cereals or other tuber crops, it offers excellent income opportunities for small and marginal farmers. The plant produces starchy, sweet-tasting tuberous roots that are rich in beta-carotene, dietary fibre, and essential vitamins. This makes sweet potato an important food security crop and a popular choice in local markets.

Understanding Sweet Potato and Its Growth Habits

Unlike the Irish potato, which is a modified stem, the sweet potato is a modified storage root. The plant belongs to the Convolvulaceae family and grows as a herbaceous perennial vine, though it is cultivated as an annual crop for commercial farming. The root system consists of thin, fibrous roots that absorb nutrients and water, and thick storage roots that accumulate starch and sugar. Understanding this growth habit is key for farmers, as all crop management decisions, from planting to fertilization, aim to maximize the development of these storage roots.

The crop is highly adaptable but needs a warm growing season. It is cultivated in the Kharif season under rainfed conditions in many parts of the country, and as a Rabi or Zaid crop in regions with assured irrigation. Major sweet potato producing states include Odisha, West Bengal, Bihar, Uttar Pradesh, Maharashtra, and Kerala. In these regions, farmers adjust the planting dates to avoid heavy rains during the harvesting phase, which can spoil the tubers and reduce their shelf life.

Climatic Conditions Required for High Yield

Sweet potato is essentially a warm-season crop that thrives in tropical and subtropical climates. It requires clear, sunny days and warm nights for optimal vine growth and tuber development. The ideal temperature range for sweet potato cultivation is between 21 and 28 degrees Celsius. When temperatures drop below 15 degrees Celsius, the growth rate slows down significantly, and the crop cannot tolerate frost. Therefore, northern Indian farmers must complete their harvest before the onset of severe winter frost.

Light is another major factor that determines the yield. Sweet potato is a sun-loving plant that requires plenty of direct sunlight. Shaded conditions lead to excessive vegetative vine growth and poor tuber formation. In terms of rainfall, an annual rainfall of 750 to 1000 mm is considered ideal. While the crop can tolerate moderate dry spells, moisture stress during the root initiation phase (which occurs 30 to 45 days after planting) will result in thin, stringy roots instead of plump, marketable tubers.

Soil Selection and Field Preparation for Shakarkand

Selecting the right soil type is crucial for obtaining shaped and uniform sweet potatoes. Well-drained, sandy loam or loamy soils with a loose texture are the best for this crop. The ideal soil pH ranges between 5.8 and 6.7. Soils that are slightly acidic to neutral promote healthy root development and reduce the incidence of soil-borne diseases. Heavy clay soils must be avoided because their compact structure restricts the swelling of the tubers, resulting in misshapen, thin, and fibrous roots that fetch lower prices in the market.

Field preparation starts with deep ploughing to a depth of 20 to 25 cm. This ensures that the soil is loose and crumbly, which is necessary for the roots to expand freely. Two or three harrowings should follow the initial ploughing to break up all clods. During the final field preparation, incorporate about 10 to 15 tonnes of well-rotted farmyard manure or compost per hectare. This organic matter improves the water-holding capacity of sandy soils and ensures proper aeration in heavier soil types.

Commercial Varieties of Sweet Potato in India

Indian agricultural research institutes have developed several high-yielding sweet potato varieties suited for different regional conditions and market preferences. For instance, Sree Bhadra is a popular variety known for its uniform, round tubers with pink skin and cream-coloured flesh. It has the added advantage of being resistant to root-knot nematodes, which are common soil pests. Another excellent variety is Sree Arun, which matures early in about 90 to 100 days and produces high yields of red-skinned tubers.

For areas where nutritional security is a priority, orange-fleshed varieties like Sree Kanaka are highly recommended due to their high beta-carotene content, which is a precursor to Vitamin A. Other notable varieties include Rajendra Shakarkand 35, CO 3, and Gouri. These varieties have different crop durations, ranging from 90 to 120 days, and varying yield potentials. Farmers should select varieties that match their local soil type, climate, and consumer demand. It is always wise to consult the nearest Krishi Vigyan Kendra for recommended cultivars in your specific district.

Nursery Management and Vine Propagation

Unlike regular potatoes, which are grown from seed tubers, sweet potatoes are propagated using vine cuttings. This propagation method is highly cost-effective and prevents the transmission of certain soil-borne diseases. To obtain healthy vines, farmers must establish a nursery. The nursery is prepared using healthy, medium-sized mother tubers collected from the previous harvest. These tubers should be free from weevil infestation and diseases.

To plant a one-hectare field, a nursery area of about 100 square meters is required. The mother tubers are planted closely on raised nursery beds. Regular watering is done to encourage quick sprouting. Within 40 to 45 days, the sprouted tubers produce vigorous vines. These vines are then cut and planted in a secondary nursery to multiply the number of cuttings, or they can be used directly for field planting if enough material is available. The cuttings should be taken from the apical portion of the vine, as they grow much faster and produce higher yields than cuttings taken from the middle or basal portions of the vine.

The vine cuttings should be 20 to 30 cm long and must contain at least 3 to 4 healthy nodes. Before planting, it is highly recommended to dip the cuttings in a bio-pesticide solution or a systemic fungicide to protect them from early fungal infections and sap-sucking insects. Storing the cut vines in a cool, shaded place for 1 to 2 days before planting helps in root initiation, leading to a better survival rate in the main field.

Ridge Planting Method and Spacing Rules

Planting sweet potato vines on ridges is far superior to planting them in flat beds. Ridge planting provides loose, aerated soil that allows the storage roots to expand without resistance. It also ensures that the excess rainwater drains away quickly from the root zone, preventing root rot. Ridges should be created at a spacing of 60 cm from centre to centre, and they should be about 25 to 30 cm high.

The vine cuttings are planted on top of these ridges at a spacing of 20 to 30 cm between plants. There are two common methods of inserting the cuttings. The first is horizontal planting, where the middle portion of the vine is buried in the soil, leaving the two ends exposed. The second is vertical or slanted planting, where the base of the cutting is inserted into the soil at an angle, ensuring that at least two nodes are buried under the surface. Both methods are effective, but vertical planting is preferred in areas with low soil moisture as the deep nodes can access water easily.

Nutrient Management for Tuber Development

Sweet potato has specific nutrient requirements that differ from other vegetable crops. While it requires nitrogen for initial vine growth, excessive nitrogen application is highly detrimental. It causes the plant to invest all its energy into growing lush green leaves, leaving the roots thin and stringy. On the other hand, potassium is the most critical nutrient for sweet potato. It is essential for starch synthesis and helps in the translocation of sugars from the leaves to the roots, promoting tuber swelling.

An indicative fertilizer dose for sweet potato is 60 kg Nitrogen, 60 kg Phosphorus, and 120 kg Potassium per hectare. Half of the nitrogen, along with the full dose of phosphorus and potassium, should be applied as a basal dose during field preparation. The remaining half of the nitrogen is applied as a top dressing 30 to 45 days after planting, right before the earthing-up operation. Farmers should always test their soil and refer to Soil Health Cards to adjust these figures according to local soil fertility levels.

Irrigation Scheduling and Moisture Control

Although sweet potato is relatively drought-tolerant once established, it requires sufficient soil moisture during the initial weeks. Immediately after planting the vine cuttings, light irrigation must be provided to ensure proper root establishment. If the soil drys out during the first ten days, many cuttings will fail to survive, resulting in an uneven plant stand.

During the active growth phase, which spans from 30 to 90 days after planting, the crop should be irrigated once every 10 to 14 days, depending on weather conditions and soil type. Sandy soils require more frequent, light irrigations than clay loams. It is vital to avoid over-irrigation, as waterlogged conditions restrict oxygen supply to the roots, causing them to rot. Irrigation must be stopped completely 10 to 15 days before the planned harvest date. This dry period allows the tubers to mature, helps in skin hardening, and reduces the water content in the roots, which increases their storage life.

Interculture Operations and Weed Control

Weed control is essential during the first 4 to 6 weeks of the crop cycle. Because sweet potato vines grow relatively slowly at first, weeds can easily outcompete the young plants for sunlight, water, and nutrients. Manual weeding or light hoeing should be done 20 to 25 days after planting. This not only removes the weeds but also loosens the soil around the ridges, promoting better root penetration.

Another critical operation is earthing up, which is carried out about 45 days after planting along with the split application of nitrogen fertilizer. Earthing up involves pulling soil from the furrows and placing it around the base of the plants to rebuild the ridges. This covers any exposed developing tubers, protecting them from direct sunlight and pests.

Vine lifting or vine turning is another specialized task in sweet potato farming. As the vines grow, they spread across the ridges and furrows. When the nodes of these vines touch moist soil, they start producing small roots. If left unchecked, these nodal roots will develop into tiny, unmarketable tubers, drawing away valuable nutrients from the primary storage roots at the base of the plant. To prevent this, farmers should gently lift the vines and flip them over occasionally to break any nodal roots. Care must be taken not to damage the main vine or pull it out from the ridge.

Managing Pests and Diseases in Shakarkand

The sweet potato weevil (Cylas formicarius) is the most destructive pest affecting this crop. The adult weevils feed on the leaves and stems, but the real damage is caused by the larvae, which bore tunnels into the stems and the developing tubers. The infested tubers produce a bitter chemical compound that makes them completely unfit for consumption or sale, even at low infestation levels.

Managing the weevil requires an integrated approach. Farmers should use only clean, pest-free vine cuttings for planting. Crop rotation with wet paddy or green manure crops helps break the pest cycle. Maintaining the ridges through regular earthing up prevents soil cracking; cracks allow the female weevils to reach the tubers to lay eggs. Installing pheromone traps at the rate of 10 to 12 traps per hectare is also highly effective in capturing male weevils and keeping the population under check.

Diseases like stem rot, soft rot, and leaf spot can also affect the crop, particularly in poorly drained fields. Stem rot is caused by a soil-borne fungus and results in yellowing of leaves and wilting of vines. To control these diseases, farmers should ensure good field drainage, treat vine cuttings with Trichoderma formulations, and remove infected plants from the field immediately.

Harvesting, Curing, and Yield Achievements

Sweet potato tubers mature in about 100 to 120 days after planting, depending on the variety. The primary sign of maturity is the gradual yellowing and drying of the leaves. To confirm maturity, farmers can dig up a few tubers and cut them. If the milky sap that flows from the cut dries quickly without turning dark or black, the tubers are mature and ready to be harvested.

Cutting the vines 3 to 5 days before harvesting is a good practice. This process, known as vine cutting, stops the translocation of moisture and hardens the skin of the tubers, making them less susceptible to bruising and skinning during harvest. Digging should be done carefully using hand forks or small spade tools to avoid cutting the tubers. Damaged tubers rot quickly and cannot be stored.

After digging, the tubers should be cured. Curing involves placing the harvested sweet potatoes in a warm, humid place (ideally 27 to 30 degrees Celsius and 85 to 90 percent relative humidity) for 5 to 7 days. This process heals any minor scratches or cuts on the skin, reduces moisture loss, and helps convert starches into sugars, which improves the sweet taste. The average yield of sweet potato under good management ranges between 15 and 25 tonnes per hectare for irrigated crops. Rainfed crops yield lower, typically between 8 and 12 tonnes per hectare. Farmers should check prices at local mandis to find the best time to sell their cured crop.

Frequently asked questions

What is the best time to plant sweet potatoes in India?

Sweet potato is planted during the Kharif season (June-July) for rainfed crops, and during Rabi (October-November) or Zaid (January-February) under irrigated conditions.

Can sweet potato be grown from regular seed tubers?

No, sweet potato is propagated using vine cuttings that are raised from mother tubers in a nursery, which ensures uniform and disease-free plant growth.

How many days does sweet potato take to mature?

Most commercial varieties of sweet potato mature in 100 to 120 days from the date of planting the vine cuttings.

Why are my sweet potatoes thin and fibrous?

Thin and fibrous roots are caused by planting in heavy clay soils, applying excessive nitrogen fertilizer, or experiencing moisture stress during the root initiation phase.

What is the ideal spacing for planting sweet potato?

Keep a distance of 60 cm between the ridges and space the vine cuttings 20 to 30 cm apart along each ridge.

How can I control the sweet potato weevil?

Control the weevil by using clean planting materials, rotating crops with wet paddy, installing pheromone traps, and earthing up to prevent soil cracks.

How many vine cuttings are needed for one acre of land?

Approximately 20,000 to 24,000 vine cuttings are required per acre, depending on the spacing adopted.

Why do we need to lift or turn sweet potato vines?

Vines are lifted to prevent them from producing roots at the nodes. Nodal roots form small, useless tubers that drain nutrients away from the main yield.

How can I tell if sweet potatoes are ready for harvest?

Leaves start yellowing. Also, cut a test tuber; if the sap dries quickly without turning dark, the crop is ready.

What is curing in sweet potato harvesting?

Curing is keeping harvested tubers in a warm, humid environment for 5 to 7 days to heal skin wounds and increase sugar content.

What is the indicative yield of sweet potato per hectare?

With good agricultural practices, irrigated sweet potatoes yield 15 to 25 tonnes per hectare, while rainfed crops yield 8 to 12 tonnes.

Which nutrients are most important for sweet potato?

Potassium is the most important nutrient for tuber size and starch synthesis, while nitrogen should be kept moderate.

Is sweet potato crop sensitive to waterlogging?

Yes, sweet potato is highly sensitive to waterlogging, which restricts oxygen in the soil and causes root rot. Good drainage is essential.

What are some popular sweet potato varieties in India?

Popular varieties include Sree Bhadra, Sree Arun, Sree Kanaka, CO 3, and Rajendra Shakarkand 35.

How should sweet potatoes be stored after harvest?

Store cured sweet potatoes in a cool, dry, and well-ventilated space. Avoid storing them in plastic bags as moisture accumulation causes decay.