Tubers (10)


Sweet Potato (Ipomoea batatas. (L.) Lam)

The sweet potato (Ipomoea batatas) is a dicotyledonous plant that belongs to the bindweed or morning glory family, Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are a root vegetable. The young leaves and shoots are sometimes eaten as greens. The sweet potato is only distantly related to the potato (Solanum tuberosum) and does not belong to the nightshade family, Solanaceae, but both families belong to the same taxonomic order, the Solanales.

The plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple. Sweet potato cultivars with white or pale yellow flesh are less sweet and moist than those with red, pink or orange flesh.

Ipomoea batatas is native to the tropical regions in the Americas. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance—some others are used locally (e.g., I. aquatica "kangkong"), but many are poisonous. The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, though that term is not usually extended to Ipomoea batatas. Some cultivars of Ipomoea batatas are grown as ornamental plants under the name tuberous morning glory, used in a horticultural context.

Although the sweet potato is not closely related botanically to the common potato, they have a shared etymology. The first Europeans to taste sweet potatoes were members of Christopher Columbus's expedition in 1492. Later explorers found many cultivars under an assortment of local names, but the name which stayed was the indigenous Taino name of batata. The Spanish combined this with the Quechua word for potato, papa, to create the word patata for the common potato.


The origin and domestication of sweet potato occurred in either Central or South America. In Central America, domesticated sweet potatoes were present at least 5,000 years ago. It has been suggested that the origin of I. batatas was between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The cultigen was most likely spread by local people to the Caribbean and South America by 2500 BCE.

The sweet potato was grown in Polynesia before western exploration, and the sweet potato cultivated in Polynesia is the Ipomoea batatas, which is generally spread by vine cuttings rather than by seeds. Sweet potato has been radiocarbon-dated in the Cook Islands to 1000 CE. A common hypothesis is that a vine cutting was brought to central Polynesia around 700 CE, possibly by Polynesians who had traveled to South America and back, and spread from there across Polynesia to Hawaii and New Zealand.

However, a 2018 study casts doubt on this hypothesis. Divergence time estimates suggest that sweet potatoes were already present in Polynesia thousands of years before humans arrived there. Additionally, there is evidence of long-distance dispersal of other species of Ipomoea from North America to Hawaii. This suggests natural long-distance dispersal of I. batatas is possible. Natural dispersal thus appears to be the simplest, most plausible explanation for the introduction of I. batatas to Oceania, although humans may have played a role in later dispersal between islands.

Dispersal in historical times
In response to a major crop failure, sweet potatoes were introduced to Fujian province of China in about 1594 from Luzon. The growing of sweet potatoes was encouraged by the Governor Chin Hsüeh-tseng (Jin Xuezeng).

The sweet potato was introduced to Okinawa, Japan, in the early 1600s. Sweet potatoes became a staple in Japan because they were important in preventing famine when rice harvests were poor. Sweet potatoes were later planted in Shōgun Tokugawa Yoshimune's private garden. It was also introduced to Korea in 1764.

The sweet potato arrived in Europe with the Columbian exchange. It is recorded, for example, in Elinor Fettiplace's Receipt Book, compiled in England in 1604.


The genome of cultivated sweet potatoes contains sequences of DNA from Agrobacterium, with genes actively expressed by the plants. Transgenes were observed both in the sweet potato's closely related wild relatives, and in more distantly related wild species. This observation makes cultivated sweet potatoes the first known example of a naturally transgenic food crop.

Cassava (Manihot esculenta Crantz)

Manihot esculenta, commonly called cassava, manioc, yuca, macaxeira, mandioca, aipim and Brazilian arrowroot, is a woody shrub native to South America of the spurge family, Euphorbiaceae. It is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates. Though it is often called yuca in Spanish and in the United States, it differs from yucca, an unrelated fruit-bearing shrub in the family Asparagaceae. Cassava, when dried to a powdery (or pearly) extract, is called tapioca; its fried, granular form is named garri.

Cassava is the third-largest source of food carbohydrates in the tropics, after rice and maize. Cassava is a major staple food in the developing world, providing a basic diet for over half a billion people. It is one of the most drought-tolerant crops, capable of growing on marginal soils. Nigeria is the world's largest producer of cassava, while Thailand is the largest exporter of dried cassava.

Cassava is classified as either sweet or bitter. Like other roots and tubers, both bitter and sweet varieties of cassava contain antinutritional factors and toxins, with the bitter varieties containing much larger amounts. It must be properly prepared before consumption, as improper preparation of cassava can leave enough residual cyanide to cause acute cyanide intoxication, goiters, and even ataxia, partial paralysis, or death. The more toxic varieties of cassava are a fall-back resource (a "food security crop") in times of famine or food insecurity in some places. Farmers often prefer the bitter varieties because they deter pests, animals, and thieves.

The cassava root is long and tapered, with a firm, homogeneous flesh encased in a detachable rind, about 1 mm thick, rough and brown on the outside. Commercial cultivars can be 5 to 10 cm (2.0 to 3.9 in) in diameter at the top, and around 15 to 30 cm (5.9 to 11.8 in) long. A woody vascular bundle runs along the root's axis. The flesh can be chalk-white or yellowish. Cassava roots are very rich in starch and contain small amounts of calcium (16 mg/100 g), phosphorus (27 mg/100 g), and vitamin C (20.6 mg/100 g). However, they are poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein (rich in lysine), but deficient in the amino acid methionine and possibly tryptophan.

Cassava is one of the most drought-tolerant crops, can be successfully grown on marginal soils, and gives reasonable yields where many other crops do not grow well. Cassava is well adapted within latitudes 30° north and south of the equator, at elevations between sea level and 2,000 m (6,600 ft) above sea level, in equatorial temperatures, with rainfalls from 50 mm (2.0 in) to 5 m (16 ft) annually, and to poor soils with a pH ranging from acidic to alkaline.

Coleus thrives well in tropical and subtropical regions. A well-drained medium fertile soil is suitable for its cultivation. 


Plant the cuttings in the main field between July and October. 

Variety: Nidhi, Sree Dhara and Suphala.
Sree Dhara _ First variety in chinese potato with good cooking quality and 5 months duration. 

Nidhi _ Variety with 5 months duration. 

Suphala _ A tissue culture mutant derived from local cultivar suited for year round cultivation with a duration of 120 - 140 days.



Raise the nursery approximately one month before planting. An area of 500 to 600 m2 is sufficient to produce cuttings required for one ha of main field. Apply 125 to 150 kg FYM in the nursery area. Plant the seed tubers at a spacing of 15 cm on the ridges taken 30 cm apart. About 170 to 200 kg of tubers is required to raise the nursery. Take the vine cutting to a length of 10-15 cm from the top portion after three weeks from planting.

Preparation of main field

Plough or dig the land to a depth of 15-20 cm and form ridges 30 cm apart or raised beds of 60-90 cm width. 


Plant the vine cutting collected from the nursery on ridges at a spacing of 30 cm or on raised beds at 30 cm x 15 cm spacing.


Broadcast 10 tonnes of FYM and N:P2O5: K2O @ 30:60:50 kg ha-1 and incorporate into the soil at the time of land preparation. Topdress with N and K2O at the rate of 30 and 50 kg ha-1 respectively at 45 days after planting.


Give weeding and earthing up, at 45 days after planting along with topdressing. Cover a portion of the vine with soil to promote tuber formation.

Plant protection

To control the root-knot nematode,deep plough the field in summer, adopt crop rotation and destroy root residues and other plant parts by burning.


Harvest the crop 5 months after planting

Tapioca grows and produces best under warm humid tropical conditions where rainfall is well distributed and fairly abundant. It can also be grown under irrigation where rainfall is low. Its outstanding characteristic in terms of moisture requirements is the ability to withstand fairly prolonged periods of drought. However, at the time of planting there must be sufficient moisture for the plant to establish itself. The crop cannot withstand cold and is killed by frost.

The crop grows well in well-drained laterite, gravelly and sandy loam soils. Heavy and rocky soils are less suitable because they restrict root development. The crop cannot survive waterlogged conditions and in such areas, it must be planted on mounds or ridges that permit drainage. The crop can also be gown on hill slopes and on wastelands of low fertility.



The main planting seasons are April-May with the onset of southwest monsoon and September-October with the onset of north-east monsoon. Planting can also be done during February-April, provided sufficient moisture is made available through irrigation. For maximum tuber production, April-May planting is preferred because the crop can effectively utilize both the monsoons. The second best season is September-October.

H-97: This is a semi-branching variety, tolerant to mosaic disease with duration of 10 months. But the harvest can be prolonged even up to 16 months. The starch content is 30 per cent.


H-165: This is a non-branching type with poor cooking quality having eight months duration. It is tolerant to mosaic but susceptible to wilt disease. The starch content is 24.5 per cent.


H-226: This is a semi-branching type with medium cooking quality having 10 months duration. It is moderately susceptible to mosaic. The starch content is 29 per cent.


M-4: This is an erect type with excellent cooking quality having 10 months duration. The starch content is 29 per cent.


Sree Visakham: This is a semi-branching type with yellow coloured flesh having 10 months duration. It shows high tolerance to mosaic and low susceptibility to pests like red mites, scale insects, thrips etc. The starch content is 26 per cent and vitamin A 466 IU.


Sree Sahya: This is a predominently semi-branching type with 10 months duration. It shows high tolerance to mosaic and low susceptibility to pests like red mites, scale insects, thrips etc. The starch content is

30 per cent.


Sree Prakash: This has seven months duration and the yield potential is 30-40 t ha-1.


Kalpaka: This is a non-branching type with six months duration and is suited as an intercrop of coconut in reclaimed alluvial soils of Kuttanad.


Sree Jaya: This is an early variety with seven months duration and excellent cooking quality. Tuber contains 24-27 per cent starch and is low in cyanogens.

Sree Vijaya: This is an early variety with 6-7 months duration and excellent cooking quality. Tuber contains 27-30 per cent starch and is low in cyanogens.

Sree Harsha: This has 10 months duration and good cooking quality. Tuber contains 34-36 per cent starch. They are non-bitter and ideal for culinary purposes and the high starch content makes it suitable for preparing dried chips.


Nidhi: This is a high yielding early variety with 5.5-6 months duration. It is tolerant to mosaic and moisture stress. Tuber contains 26.8 per cent starch and 20 ppm HCN.


Vellayani Hraswa: High yielding early variety with 5-6 months duration. It cannot tolerate drought. The cooking quality is very good. Tubers contain 27.8 per cent starch and 53 ppm cyanogen.


Sree Rekha: It is a top cross hybrid with 10 months duration. Tubers contain 28.2 per cent starch with excellent cooking quality.


Sree Prabha: It is a top cross hybrid with 10 months duration. Tubers contain 26.8 per cent starch with good cooking quality.


Seeds and sowing

Tapioca is propagated from cuttings. Select mature healthy stems free from diseases or pests. Discard about 10 cm from the lower mature and about 30 cm from the upper immature end. Stems should be cut into setts of 15-20 cm length using a sharp knife. About 2000 stems are required for planting one hectare. Harvested stems are to be stored vertically in shaded and well-aerated places. Spraying dimethoate (0.05 per cent) on the stem will control scale insects.


Pit, flat, ridge or mound method of planting can be adopted depending upon soil type, topography of land and elevation so that waterlogging is avoided. Pit followed by mound is found to be the best method of planting. Plant the cuttings vertically after smoothening the lower cut end, at a depth not exceeding 4-6 cm. Adopt square method of planting at a spacing of 90 cm x 90 cm @ one cutting per pit. It is preferable to adopt 75 cm x 75 cm spacing for non-branching varieties like M-4.


Gap filling should be done within 15 days after planting preferably with longer setts of 40 cm length. Sree Visakham is a choice variety recommended as an intercrop in coconut gardens. Optimum plant population is 8000 plants per ha with 90 cm x 90 cm spacing.


Land Preparation

Before planting, plough the field 2-3 times or dig to a depth 25-30 cm depending upon soil type to establish a deep porous field in which the setts are to be planted.


Minisett planting technique for quality planting material
For producing minisetts, mature, disease free stems preferably those obtained from indexed meristem culture should be selected. Two node cuttings are taken from these stems using a sharp hack-saw. Top one-third portion is usually discarded in the traditional system, however in the minisett technique, it is fully utilized. The tip of the stem (about 5 to 6 cm long) is carefully cut without causing damage. For preventing dehydration, it is advisable to place the tip cuttings in water. The stem just below the growing tip is very tender with prominent axillary buds. Hence, from this portion, cuttings with four nodes are taken instead of two as the latter may easily get dried up.

Preparation of nursery:

Select an area with well drained soil and irrigation facility. Shade net house of 35 per cent shade is ideal for the germination and growth of minisetts. Mark out the length and breadth and make raised beds of soil : sand mixture in equal proportion. The beds could be of convenient length and width not exceeding 1 m. An area of 220 m2 nursery is required for producing minisetts for planting one hectare of land. Two node cuttings are planted end to end horizontally, about 5 cm deep inside the soil, with the buds facing either sides. Tip cuttings and four node top setts should be planted erect at 5 cm x 5 cm spacing to prevent decay due to excess moisture in these tender parts. Minisetts would sprout in a week's time. Mosaic virus infected plants, if any found, should be rogued off as soon as such symptoms are expressed, to keep the nursery disease free. The minisetts will be ready for transplanting in about three to four weeks time. After the basal application of recommended manure in the main field, ridges of 30 cm height are taken with a spacing of 45cm between the ridges and planting is done on the ridges at a spacing of 45 cm. Multiplication ratio by this process is enhanced to 1: 60 as against the traditional method 1:10.



Cattle manure or compost may be applied at 12.5 t ha-1 during the preparation of land or while filling up the pits so as to provide about 1 kg of organic manure per plant. Apply fertilizers N:P2O5:K2O at the rates (kg ha-1) shown below:


H-97 and H 226 :              75:75:75
H-165, Sree Visakham,    100:100:100

Sree Sahya:             

M-4 and local:                 50 :50 : 50


N and K2O may be applied in three split doses, i.e., 1/3 basal, 1/3 two months after planting and 1/3 three months after planting. Dose of P2O5 can be reduced to half where the crop is grown for more than 3 years under full dose of recommended fertilizers, since under such situation there would be build up of soil P.


For August-September planted tapioca, apply half N, full P2O5 and half K2O basally with first digging and weeding. The remaining quantity of N and K2O may be applied 45 days after planting at the time of intercultivation.


In the acid soils of Kerala, 50 per cent of K requirement can be substituted by NaCl.

Note: N:P2O5:K2O at 50:50:100 kg ha-1 is recommended for Sree Visakham when grown as an intercrop in coconut garden. Higher levels of N tend to increase HCN content of the tubers.


Soil application of Mg as MgSO4 @ 20 kg ha-1 (1.62 g/plant) and Zn as ZnSO4 @12.5 kg ha-1 (1g/plant) in small channels around the mounds within 2 months of planting cassava providing an interval of 2 weeks between the application of these fertilizer enhances tuber yield and quality. When they are used continuously, their application rates can be fixed based on their status in the soil following the table given below:




Keep the field free of weeds and maintain soil loose by 2-3 shallow diggings or hoeing upto 90 days after planting followed by light earthing up. Retain two shoots on each plant in opposite directions and remove excess shoots about 30 days after planting.



Under conditions of well-distributed rainfall, tapioca grows well as a rainfed crop and irrigation is not necessary. However, the crop has to be irrigated to provide sufficient moisture under conditions of prolonged dry periods after planting. When the crop is grown under irrigation, yield increase of 150-200 per cent over the rainfed crop has been observed.


Furrow irrigation with 25 mm water at 100 mm CPE and alternate furrow irrigation with 50 mm water at 75 mm CPE require only less water and labour for optimum yield. Approximate irrigation interval schedules will be 27 and 20 days respectively in summer months.


Intercropping in tapioca

Tapioca is planted at a spacing of 90 cm x 90 cm and it takes about 3-3.5 months time to have enough canopy to cover the land. So it is possible to have an intercrop of groundnut during the early stages of tapioca crop. Bunch varieties like TMV-2, TMV-7, TG-3, TG-14 and Spanish improved are preferred for intercropping in tapioca. The best season for sowing groundnut is May-June. Immediately after planting of tapioca setts, groundnut seeds are sown at a spacing of 30 cm between rows and 20 cm within rows, so that two rows of groundnut can be accommodated in between two rows of cassava. A seed rate of 40-50 kg ha-1 is recommended for dibbling one seed per hill. Only well-matured and bold seeds are to be selected for sowing. In acid laterite soils of Kerala, apply 1000 kg ha-1 of lime as basal dressing. A basal dose of 50:100:50 kg N:P2O5:K2O per ha should be given uniformly to both the crops. One month after sowing of the seed, 20 kg each P2O5 and K2O and 10 kg N / ha-1 may be given to the intercrop along with earthing up. Once pod formation has started (i.e., 40-45 days after sowing) the soil should not be disturbed, as it will affect the pod development adversely. The groundnut crop matures in 105 to 110 days. After the harvest of pods, the haulms are incorporated in the soil along with a top dressing of 50 kg each of N and K2O per ha for the main crop. By adopting this practice, 20-25 per cent additional income can be obtained.


In sandy areas intercropping tapioca with cowpea / groundnut / black gram / green gram may be recommended giving a spacing of 20 cm on both sides of the ridges. The non-trailing grain cowpea variety V-26 is recommended as a companion crop along with tapioca. For a pure crop of tapioca or for a cropping system involving tapioca as the main crop and the pulse crop suggested above, the field may be irrigated once in 36 days to a depth of 5 cm. This recommen-dation is for shallow water table situations. For deep water table situations, the crop may be irrigated once in 24 days to a depth of 5 cm.


Plant protection

Cassava mosaic disease (CMD)
The disease is transmitted by a white fly Bemisia sp. As a rule, only stem cuttings from disease free plants should be used for planting to minimize the spread of the virus disease. For this purpose, tagging of disease free healthy plants for selection as planting materials must be practised from September to December. All plants showing even very mild symptoms must be rejected. Mosaic tolerant varieties such as H-97 may be used to minimize economic loss of tubers.


Production of disease free planting material of tapioca through nursery techniques

Setts of 3 to 4 node cuttings from apparently disease free plants are collected and planted in the nursery at a very close spacing of 4 x 4 cm so that about 500 setts can be accommodated in one square metre land. Daily watering of the setts has to be done for the first 10 days and on alternate days afterwards. Screening of CMD symptoms may be started 10 days after planting. Setts showing even mild symptoms are to be removed and burnt. This must be continued up to 20-25 days, by that time healthy seedlings can be transplanted to the main field. Supplementary irrigation may be given in the transplanted field till they get established. Screening for disease symptoms and roguing of infested plants may be continued in field at weekly intervals upto harvest. The selected healthy stems are again cut into minisetts and subjected to nursery and field screening. By adopting this technique it is possible to produce healthy plants.


Leaf spot

Spray 0.2 per cent zineb or 1 per cent Bordeaux mixture for control of leaf spot.


Bacterial blight

Bacterial blight is a disease noted in severe proportion in certain parts of Kerala. Chemical control is not effective. Use of resistant or tolerant varieties is the only method of control. Among improved varieties, H-97, H-226, H-1687 and H-2304 are tolerant to the disease while H-165 is highly susceptible. Among the local varieties, M-4, Paluvella, Pichivella, Parappilppan, Anamaravan etc. are tolerant to the disease.


Red spider mites and scale insects

Red spider mites in the field and scale insects under storage are important pests of tapioca. Under field conditions light infestation of mites can be controlled effectively by spraying the crop with water at 10 days interval from the onset of mite infestation. In the case of very severe infestation, the crop can be protected by spraying 0.05 per cent dimethoate at monthly intervals from the time of appearance of mites. The stem may be sprayed with 0.05 per cent dimethoate before storing as a prophylactic measure against the scales.


To control termites infesting planted setts, sprinkle a little of carbaryl 10 per cent or chlorpyrifos in the mounds prior to planting.


Management of storage pests of cassava

Treating chips with granular salt (3 per cent), sun drying thoroughly and storing in gunny bags in godown are very effective against Araecerus fasciculatus and Sitophilus oryzae.



Tapioca becomes ready for harvest 9-10 months after planting. Hybrid varieties like H-226, H-97 and H-165, when grown under recommended management practices have recorded yields up to 40-50 t ha-1 of raw tuber.

Sweet potato requires a warm humid tropical climate with a mean temperature of about 22 ºC. Though sensitive to frost, it can also be grown in the hills up to an altitude of 1500-1800 m as a summer crop. Under rainfed conditions the crop requires a fairly well distributed annual rainfall of 75-150 cm. Being a photosensitive crop, sunny days and cool nights are favourable for better tuber development. The crop can be grown on a variety of soils having good drainage, but grows best in fertile sandy loam soils. Heavy clayey and very light sandy soils are not suitable for proper tuber development.



Rainfed crop: June-July, September- October


Irrigated crops: October-November (for uplands) and January- February (for low lands)



Improved varieties: H-41, H-42, Sree Nandini, Sree Vardhini, Sree Rethna, Sree Bhadra, Kanjanghad, Sree Arun, Sree Varun and Sree Kanaka.

H-41 _ Variety with excellent cooking quality, sweet tubers and duration of 120 days.

H-42 _ Variety with excellent cooking quality, sweet tubers and duration of 120 days.

Sree Nandini _ Early maturing, drought tolerant variety with 100 - 105 days duration and suited as catch crop in paddy fallows.

Sree Vardhini _ Early maturing, carotene rich variety for food and feed with a duration of 100 - 105 days.
Sree Rethna _ Early maturing, carotene rich orange fleshed variety with 90 - 105 days duration.
Sree Bhadra _ Early maturing, (90 days), trap crop for nematodes. 
Sree Arun Early maturing, (90 days),

Sree Varun highly palatable varieties.

Sree Kanaka _ Short duration (75 - 85 days) variety with very high carotene (8.8 - 10 mg/100 g).

Kanjanghad _ KAU variety obtained through selection and duration of 105 - 120 days

Local varieties: Badrakali Chuvala, Kottayam Chuvala, Chinavella, Chakaravalli, Anakomban.


Seeds and sowing

Sweet potato is propagated by means of vine cuttings. To obtain vine cutting, raise nurseries from selected tubers using the following method. Eighty kg of medium sized weevil free tubers (each of 125-150 g) are required for planting in the primary nursery area (100 m2 to plant one hectare).


Plant the tubers at a spacing of 30-45 cm on ridges formed at 60 cm apart and replant in secondary nursery of about 500 m2 area at a spacing of 25 cm. Apply urea 15 days after planting at 1.5 kg / 100 m2 in the 
primary nursery. To ensure better plant growth in the secondary nursery, 5 kg of urea has to be applied in two split doses on 15th and 30th day after planting. Vines obtained from the freshly harvested crop are also planted in similar nursery area to obtain sufficient planting material. Cuttings obtained from the apical and near apical portions of the vines are preferable for planting in the main field. Storing of cut sweet potato vines with intact leaves, in bundles covered with banana leaves (dipped in water) and kept under shade for two days prior to planting is recommended. Irrigate the nursery every alternate day during the first 10 days and once in 10 days, thereafter. Vines will be ready for planting on the 45th day.


In the main field, plant vine cutting of 20-25 cm length on ridges 60 cm apart and at a spacing of 15-20 cm between the vines. The cuttings can also be planted on mounds taken at a spacing of 75 cm x 75 cm. On the top of each mound, 3-6 cuttings can be planted. Plant the vine cuttings with the middle portion buried deep in the soil and the two cut ends exposed to the surface. Ensure sufficient moisture in the soil for early establishment of the cutting. Provide adequate drainage and prevent water logging.


Land Preparation

Make the soil to a fine tilth by ploughing or digging to a depth of 15-25 cm. Make ridges 25-35 cm high, 60 cm apart for planting vines.


Apply cattle manure or compost at 10 t ha-1 at the time of preparation of ridges. The recommended N:P2O5:K2O dosage for sweet potato is 75:50:75 kg ha-1. For the reclaimed alluvial soils of Kuttanad, the recommendation is 50:25:50 kg/ha. Apply N in two equal split doses, the first at the time of planting and the second 4-5 weeks after planting. Apply full dose of P2O5 and K2O at the planting time.



When grown as irrigated crop, provide irrigation once in 2 days for a period of 10 days after planting and thereafter once in 7-10 days. Stop irrigation 3 weeks before harvest. But one more irrigation may be given 2 days before harvest. IW / CPE for higher tuber yield in non-rainy periods is 1:2 (approximate interval of 11 days). The application of N and K2O at the rate of 50 kg/ha is recommended for the crop grown under irrigation.



Conduct two weeding and earthing up operations about 2 weeks and 5 weeks after planting. The top dressing of fertilizers may be done along with the second aftercultivation. Prevent development of small slender tubers at the nodes by turning the vines occasionally during active growth phase.


Rotation and mixed cropping

Under irrigated conditions, sweet potato can be rotated with rice and planted during December-January after harvest of the second crop of rice. As a mixed crop, it can be grown along with colocasia, elephant foot yam etc. Under rainfed conditions, green manure crops such as kozhinjil and sunnhemp can be grown after harvest of the sweet potato and later incorporated into the soil at the time of land preparation for the succeeding crop.


Plant protection

Integrated control of sweet potato weevil

a) Remove and destroy the crop residues of the previous crop.

b) Use healthy and weevil-free planting materials.
c) Apply Chromolaena odorata leaves as mulch @ 3 t ha-1 at 30 DAP.

d) Trap adult weevils using sweet potato pieces (of about 6 cm diameter) of 100 g size, kept at 5 m apart during 50 to 80 DAP at 10 days interval. Tubers may be cut and kept inside wire cages to avoid rat damage.

e) Use pheromone traps (3Z dodecenyl 2E butenoate).



The duration of the crop depends on the variety; but in general, the crop can be harvested in about 3.5 _ 4 months after planting. Harvest the crop when leaves begin to turn yellow and the tubers mature. The maturity of tuber can be ascertained by cutting fresh tubers. The cut surface will dry clear if the tuber is mature and becomes dark green if immature. Harvest the crop by digging out the tubers without causing injury.

White yam or African yam is a new crop species of edible yam introduced from Nigeria.


Sree Subhra: The tuber contains 27-28 per cent dry matter, 21-22 per cent starch and 1.8-2 per cent protein. It is drought tolerant with 9-10 months duration.

Sree Priya: The tuber contains 25-27 per cent dry matter, 19-21 per cent starch and 2-2.5 per cent protein. It is drought tolerant and duration is 9-10 months. It is suitable for inter-cropping in mature coconut garden and with banana.
Sree Dhanya: It is the first dwarf variety. The tubers have 28-30 per cent dry matter, 22-24 per cent protein and 0.3-0.5 per cent sugar.



FYM 15 t ha-1 to be applied at the time of land preparation followed by application of NPK fertilizers @ 100:50:100 kg ha-1. Full dose of P fertilizer along with 50 per cent of N and K fertilizers to be applied as basal when 50 per cent of the planted setts sprouts. The balance 50 per cent of N and K fertilizers to be applied as top dressing, 1 month after the basal dressing which could be combined with intercultural operations. 


Rapid seed yam production (minisett technique)
In this method clean and healthy yam tubers weighing about 1 kg are cut into cylindrical (disc-like) pieces, each about 5 cm thick. From each such piece, 2-4 small pieces (30 g) could be obtained by cutting the disc longitudinally or along the two perpendicular diameters. Such a piece is called a "minisett". The minisetts are then spread out under light shade for an hour with cut surface facing up before planting them in the nursery seedbeds. The minisett takes 2-3 weeks for sprouting. At this stage, they are transplanted to the main field at a spacing of 50 cm on ridges taken 1 m apart.

It is grown in a similar agro-climatic situation as that of D. alata. Planting season and manuring are also similar.



(1) Sree Latha: This is a selection from Thiruvananthapuram district with a duration of 8 months. Tubers are oblong to fusiform with creamy white flesh. Vines twine to the left.

(2) Sree Kala: This is an early variety with 7.5 months duration. The tubers have 35-37 per cent dry matter, 23-25 per cent starch and 1-1.3 per cent sugar.


Seeds and sowing

Select medium size tubers weighing about 100-150 g each. Plant the whole tuber, one in each mound and cover completely with soil. Mulch the mounds to maintain optimum temperature and moisture. To plant one hectare 1800-2700 kg of seed materials are required.

Preparation of land

Plough or dig the land to a depth of 15-20 cm. Prepare mounds at a spacing of 75 cm x 75 cm incorporating cattle manure @ 1 kg per mound.



The fertilizer dose and schedule of application are the same as that of D. alata.



Trail the vines by fixing small poles attached with coir rope and direct 4-6 plants per pole.


The crop is ready for harvest by about 7-8 months time. Tuber yields of 20-25 t ha-1 can be obtained by following the improved methods of cultivation.

1 Greater yam is predominantly a tropical plant. The crop cannot withstand frost and excessively high temperatures. Temperature around 30ºC and rainfall of 120-200 cm distributed throughout the growth period are ideal. Day length greater than 12 hours during initial stages and shorter day length during the later part of the growing season favour satisfactory tuber formation. Yam requires loose, deep, well-drained, fertile soil. The crop does not come up well in waterlogged conditions.



Seed tubers are normally planted during the later part of the dry season (March-April) and start sprouting with the onset of pre-monsoon showers. If the planting is delayed, yams start sprouting in storage, which is not desirable for planting.



1. Sree Keerthi: Suitable for intercropping in mature coconut garden and with banana.
2. Sree Roopa: Possesses excellent cooking quality.

3. Indu: This is recommended as a pure crop and also as an intercrop of coconut in the reclaimed alluvial soils of Kuttanad.

4. Sree Shilpa: This is the first hybrid having good culinary quality. The crop matures early, within 8 months. The tubers have 33-35 per cent dry matter, 17-19 per cent starch, 1.4-2 per cent protein and 0.8-1.2 per cent sugar.

5. Sree Karthika : High yiled, excellent cooking quality. The crop matures within 9 months. The tubers have 21.42 per cent starch, 1.14 per cent sugar and 2.47 per cent crude protein. 

Seeds and sowing

D. alata produces mostly a single big tuber in which only one head end of the tuber is available as good seed material. For getting the head end in each propagation unit, the whole tuber is divided longitudinally. Each piece of cut tuber should weigh at least 250-300 g. Dip the pieces in cowdung slurry and allow to dry under the shade before planting. About 2500-3000 kg of seed material is required to cover one hectare of land.


Preparation of land

Plough or dig the land up to a depth of 15-20 cm. Dig pits of size 45 x 45 x 45 cm at a distance of 1 x 1m. Fill up three fourth of the pits with 1-1.25 kg cattle manure or compost and mix with topsoil. Plant the cut

tuber pieces and completely cover the pit with leafy materials to conserve soil moisture and maintain optimum temperature.



Apply cattle manure or compost at 10-15 t/ha as basal dressing. A fertilizer dose of 80:60:80 kg of N:P2O5:K2O per ha has to be applied in two splits; half dose of N, full P2O5 and half of K2O within a week after sprouting; remaining half N and half K2O one month after the first application along with weeding and earthing up.

Plant protection

Yam scale is found to infest the corms both under field and storage situations.



Trailing is essential to expose the leaves to sunlight. Trailing has to be done within 15 days after sprouting by coir rope attached to artificial supports in the open areas or to trees where they are raised as an intercrop. When grown in open areas, trail to a height of 3-4 m. Trail the vines properly as and when side shoots are produced.


The crop becomes ready for harvest within 8-9 months after planting when the vines are completely dried up. Dig out the tubers without causing injury.

Colocasia is a crop of tropical and sub-tropical regions and requires a warm humid climate. Under rainfed conditions, it requires a fairly well distributed rainfall around 120-150 cm during the growth period. Well-drained soil is suitable for uniform development of tubers.



Rainfed crop : May-June to Oct-Nov.

Irrigated crop : Throughout the year



Sree Rashmi, Sree Pallavi and Sreekiran are three improved varieties.

Sree Rashmi - Economic yield under low input levels, conical cormets and 7 months duration.

Sree Pallavi - Field tolerant to leaf blight and mosaic, club shape cormets and 7 months duration.
Sreekiran - First hybrid taro variety in India, long keeping quality of cormets and 61/2 - 7 months duration.


Seeds and sowing

Use side tubers each of 25-35 g for planting. About 37,000 side tubers weighing about 1200 kg are required to plant one hectare.


Plough or dig the land to a depth of 20-25 cm and bring to a fine tilth. Make ridges 60 cm apart. Plant the side corms at a spacing of 45 cm on the ridges.



Apply cattle manure or compost @ 12 t ha-1 as basal dressing, while preparing the ridges for planting. A fertilizer dose of 80:25:100 kg of N:P2O5:K2O per ha is recommended. Full dose of P2O5 and half dose of N and K2O should be applied within a week after sprouting and the remaining half dose of N and K2O one month after the first application along with weeding and earthing up.


Inter-cultivation is essential in colocasia. Weeding, light hoeing and earthing up are required at 30-45 days and 60-75 days after planting. The leafy parts may be smothered about one month before harvest so as to enhance tuber development.


Ensure sufficient moisture in the soil at the time of planting. For uniform sprouting, irrigate just after planting and one week later. Subsequent irrigation may be given at 12-15 days intervals, depending on the moisture retention capacity of the soil. The irrigation should be stopped 3-4 weeks before harvest. About 9-12 irrigations are required for the crop till harvest. In the case of rainfed crop, if there is prolonged drought, supplementary irrigation is required.



Soon after planting, cover the ridges with suitable mulching materials for retention of moisture and to control weeds.


Plant protection

Colocasia blight can be controlled by spraying zineb, mancozeb or copper oxychloride formulations at 2 g l-1of water (1 kg ha-1). For controlling serious infestation of aphids, apply dimethoate at 0.05 per cent. Leaf feeders can be controlled by applying malathion or carbaryl.


Colocasia becomes ready for harvest five to six months after planting. The mother corms and side tubers are separated after harvest.


Storage of seed material

The side tubers to be used as planting materials are usually separated from the mother corm and stored. Keep seed tuber in sand spread over the floor to avoid rotting.

Elephant foot yam requires fairly long growing season and a rainfall of about 150 cm during the crop period. A well-drained soil of medium texture is suited for this crop.



Corm pieces are normally planted during February-March, before the onset of monsoon.



Sree Padma: The crop matures in 8-9 months. Cooked tubers are free from acridity.

Sree Athira; First genetically improved variety with very good cooking quality.


Seeds and sowing

Tuber cut-pieces weighing about 1 kg are ideal for planting. Dip the pieces in cowdung slurry and allow to dry under shade before planting. Nematodes associated with amorphophallus can be controlled by seed material treatment with talc based formulation of Bacillus macerans @ 3g (106 cfu/g) per kg of corms. After planting, cover the pit with dried leaves or other mulching materials. About 12,000 cut pieces weighing about 12 t are required for planting one hectare. Most of the seed material will germinate within one month after planting.

Mealy bugs usually attack the corm in field and store. Avoid planting corms already infested.


Land Preparation

Dig pits of 60 cm x 60 cm x 45 cm size 90 cm apart. Collect the topsoil to a depth of 15-20 cm separately and fill it after the pits are formed. Apply cowdung or compost at 2-2.5 kg/pit and mix with topsoil.


Minisett technique for quality planting materials

Minisetts weighing 100 g each can be planted directly in nursery beds or in the main field with the central bud portion facing up at a spacing of 60 cm x 45 cm. A total of 37,000 minisetts/ha is required as against 12,345 setts/ha in the traditional method. Multiplication ratio in elephant foot yamcould be enhanced to 1:15 as against the conventional 1:3 by adopting minisett technique.


After cultivation

Apply full dose of P2O5 and half the dose N and K2O (N:P2O5:K2O @ 50:50:75 kg ha-1) after forty five days of planting along with intercultivation and weeding. Apply second dose of fertilizers (N and K2O @ 50:75 kg ha-1) one month after the first application along with intercultivation and earthing up.


The crop will be ready for harvest 8-9 months after planting.


Organic farming technology for elephant foot yam


• Raising green manure cowpea (seed rate @ 20 kg ha-1) prior to elephant foot yam and incorporation of green matter at 45-60 days.

 Use of organically produced planting materials.

 Treatment of corm pieces of 500-750 g with slurry containing cowdung, neem cake and Trichoderma harzianum (5 g/kg seed) and drying under shade before planting.

 Application of Trichoderma harzianum incorporated FYM @ 36 t ha-1 (3 kg/pit) in pits at the time of planting (FYM neem

cake mixture (10:1) inoculated with Trichoderma harzianum @ 2.5 kg/tonne of FYM neem cake mixture. Trichoderma can be multiplied in FYM alone but it will take 15 days to form sufficient inoculam as against 7-8 days if neem cake is also used along with FYM). This is effective against collar rot caused by Sclerotium rolfsii.

 Application of neem cake @ l.0 t ha-1

(80-85 g/pit) in pits at the time of planting.

 Inter-sowing of green manure cowpea (seed rate @ 20 kg ha-1 ) between elephant foot yam pits and incorporation of green matter in pits a i 45-60 days. The green matter addition from the 2 green manure crops should be 20-25 t ha-1.

 Application of ash @ 3 t ha-1 (250 g/pit) at the time of incorporation of green maure in pits.