Ipomoea aquatica (PROSEA)
Ipomoea aquatica Forsskal
- Protologue: Fl. Aegypt.-Arab. 44 (1775).
- Family: Convolvulaceae
- Chromosome number: 2n= 30
- Ipomoea reptans auct.
- Kangkong, water convolvulus, water spinach (En)
- Patate aquatique, liseron d'eau (Fr)
- Brunei: kangkong (Bukit Udal)
- Indonesia: kangkung (general), kalajau (Minangkabau), pangpung (Balinese)
- Malaysia: kangkung, kankong
- Papua New Guinea: kangkong, kango
- Philippines: kangkong (Tagalog), balangog, galatgat (Iloko)
- Cambodia: trâkuön
- Laos: phak bong
- Thailand: phakbung (general), phak-thotyot (central), kam-chon (northern)
- Vietnam: rau muống, ung thái.
Origin and geographic distribution
Kangkong originated in tropical Asia (possibly India) and can be found in South and South-East Asia, tropical Africa, South and Central America and Oceania. Only in South and South-East Asia is kangkong an important leafy vegetable. It is intensively grown and frequently eaten throughout South-East Asia, Hong Kong, Taiwan and in southern China.
The young tops or plants (stem and leaves) are cooked or lightly fried in oil and eaten in various dishes. The vines are used as fodder for cattle and pigs. In Malaysia it is widely grown in fish ponds by the Chinese who feed it to their pigs.
In Brunei, fried leaves are eaten to cool down a fever. In Indonesia, a decoction of the roots is used as a wash against haemorrhoids, and also as a laxative, tonic and antidote against opium or arsenic poisoning or drinking of unhealthy water. The crushed leaves are put on sores and boils.
Production and international trade
Production figures are difficult to obtain due to the lack of any registration of information on production and trade. In Thailand and Malaysia white-flowering kangkong is the second most widely grown leafy vegetable after pak choi (Brassica rapa L. cv. group Pak Choi). Red kangkong is collected from the wild and consumed in rural areas of Malaysia, but in Thailand and Singapore it is sometimes sold in the markets as well. In Indonesia the harvested area is estimated at 10 000 ha (1988), mainly of paddy-field kangkong, planted by stem cuttings and harvested by monthly ratooning during nine months of the year. In Malaysia the area under cultivation is estimated to be 600-1100 ha with a total production of 60 000-220 000 t/year. Marketing in Thailand, Malaysia and Singapore is usually done by middlemen. Kangkong is exported from Bangkok to Hong Kong and to a lesser extent to European countries.
Kangkong seed is produced on a commercial scale in Hong Kong, China, Taiwan, Thailand, the Philippines and Japan. In Malaysia 20% of kangkong farmers grow their own seed. Thailand is the leading seed producer of the region with 700-900 t per year, of which about 500 t is exported to neighbouring countries. The bulk of the seed is still landrace Phakbung-chin produced by paddy farmers in Nakhon Pathom Province as an additional cash crop. The seed trade in Malaysia and Singapore is not well organized. Chinese middlemen import seed from Thailand and Taiwan. Malaysia imports about 180 t of seed annually.
Unfortunately, most sources do not state whether only leaves or stems and leaves were analysed. The higher the ratio of leaf-blades to petioles and stems, the higher the nutritional value. Mean values per 100 g edible portion are: water 90.2 g, protein 3.0 g, fat 0.3 g, carbohydrates 5.0 g, fibre 1.0 g, ash 1.6 g, Ca 81 mg, Mg 52 mg, Fe 3.3 mg, provitamin A 4000-10 000 IU, vitamin C 30-130 mg. The energy value is 134 kJ/100 g. The 1000-seed weight is ca. 40 g.
- A perennial or sometimes annual, fast growing herb, 2-3 m long, trailing or floating, stem hollow or spongy, succulent, smooth, rooting at the nodes, nodes glabrous or hairy.
- Leaves alternate, variable, triangular to lanceolate, 2.5-15 cm × 1-9 cm, base cordate or hastate, basal lobes entire or dentate, petiole 3-20 cm long, green or purple.
- Flowers solitary or in a few-flowered cyme, peduncle 1-12 cm long; pedicel 2-6.5 cm long, sepals subequal, 7-8 mm long, corolla funnel-shaped, 4-7.5 cm long, pink or pale lilac, throat purple or magenta, rarely white, filaments hairy at base, ovary glabrous
- Capsule ovoid, 7-10 mm long, smooth, brown, partly enclosed by the calyx.
- Seeds 2-4, 4 mm long, angular to rounded, glabrous or velvet, black or light to dark brown, greyish pubescent or glabrous.
- Seedling exhibits epigeal germination, with horseshoe-shaped cotyledons.
Growth and development
Germination rates of kangkong are usually low (< 60%) and vary with the colour of the seed-coat, being highest in the black-seeded types. The hard-seededness may be influenced by the length of time between cutting the plants and threshing. There is also evidence that emergence behaviour has a strong genetic component. Plants start developing lateral branches from cotyledonary buds 2-3 weeks after sowing. Thereafter the main axis and both laterals each produce about one leaf every 2-3 days. Harvesting may start 20-30(-50) days after sowing. Flowering is required only for seed production, and under conducive conditions may start 48-63 days after sowing.
Other botanical information
Ipomoea reptans Poiret (1814) is an incorrect synonym which is often used.
Two types of kangkong are distinguished in South-East Asia:
- Red kangkong: plants with green/purple stems, dark green leaves with sometimes purple petioles and veins, and light purple to white flowers. Plants of this group can be found growing wild in tropical South-East Asia (Indonesia and Malaysia: kangkung air; Thailand: phakbung-thai). Flowering and seed set do not always occur. In Thailand and Malaysia, red kangkong is gathered by the local population for food and as animal feed.
- White-flowering kangkong: plants with green/white stems, green leaves with green/white petioles, and white flowers. This type is generally cultivated in South-East Asia (Indonesia: kangkung darat; Malaysia: kankung putih, kankung darat; Thailand: phakbung-chin). In the Philippines and Taiwan two cultivars of white-flowering kangkong are distinguished: one with broad leaves and one with narrow and pointed leaves. Recently, cultivars have been developed in Thailand, including "Loet Phan nr. 1" (green stems, quick and uniform emergence), "Bai Phai nr. 5" (dark green leaves and stems, very narrow leaves known as bamboo-leaf type), and "Prachan nr. 9" (yellow green leaves, whitish stems). The Thai landrace Phakbung-chin is still very important.
I. aquatica occurs in moist, marshy or inundated localities, shallow pools, ditches, rice fields, forming dense masses, and also along roadsides, wild and cultivated, from sea-level up to 1000 m altitude.
Probably kangkong is a quantitative short-day plant. It produces optimum yields in the lowland humid tropics, with stable high temperatures and short-day conditions. Kangkong is a typical lowland vegetable. It is rarely grown above 700 m because at average temperatures below 23°C the growth rate is too slow to make it an economic crop. At higher latitudes (North Thailand, North Vietnam, Hong Kong), it is mainly grown as a summer vegetable. Adapted to a wide range of soil conditions, kangkong has a relatively high soil moisture requirement and clay soils are generally suitable. Soils with a high level of organic material are preferable. The optimum pH is between 5.3-6.0.
Propagation and planting
Kangkong can be grown in various ways. In Malaysia, Taiwan, Thailand and Vietnam it is usually cultivated as an upland crop (e.g. the "Chinese market-gardening system" or the "ditch-and-dike system" in Thailand), but in Indonesia it is mainly grown in water (e.g. "paddy-field kangkong" or "floating kangkong").
- Upland or dry cultivation. Under these conditions kangkong roots in soils which are not inundated. Seeds are either broadcast or sown in rows (in Malaysia, Singapore and Thailand). In Thailand the seeds are sometimes soaked for 12-24 hours in water before sowing, but in the leading production areas, soaking is not practised. When seeds of reliable quality are available, Thai farmers use about 80 kg/ha. If necessary, soils are limed before sowing (2500 kg/ha). Besides seed, cuttings are used for propagation in China and Taiwan. Cropping takes place on beds. Plant densities may vary between 30-170 plants/m2. A quick and uniform emergence is an important consideration for farmers.
- Paddy-field or wet cultivation. Paddy-field kangkong is practised in Indonesia, the Philippines, Thailand, China, Taiwan, Hong Kong and India. Planting may be direct by cuttings or by transplanting 6-week-old seedlings raised on nursery beds (in China, Taiwan and Hong Kong). Planting densities may vary widely from 200 000-1 500 000 cuttings or seedlings per ha. Floating kangkong is mainly grown on a commercial scale in ponds and rivers in Thailand, China and Taiwan. Integrated systems with fish, kangkong, pigs and chickens are practised. There is no root contact with the soil. Cuttings are anchored in the water by bamboo sticks forming a kind of bed.
- Upland cultivation. Weeding and watering are normally done by hand. Chicken, duck and pig manure are used as a basic application in Thailand, Malaysia and Singapore. Night soil is no longer permitted as manure in these countries. Fertilizers (e.g. ammonium sulphate, urea) are used as a top dressing immediately after sowing and 10-15 days later. In China, night soil is the most important fertilizer for kangkong. Application of higher levels of nitrogen fertilizer does not solely increase yields; leaf/stem ratios and dry matter content, especially of stems and petioles, decrease while nitrate content increases. Therefore, the amount of nitrogen available in the soil plus that provided as fertilizers should be monitored to avoid unacceptably high amounts of nitrate in the produce.
- Paddy-field cultivation. The water level is raised according to the development of the crop. Young plants cannot withstand flooding. In China and Hong Kong night soil is applied diluted with irrigation water. In Taiwan, a basic application of 10 t/ha of cow dung is followed by a top dressing of 50 kg/ha of ammonium sulphate after each harvest. In the Bangkok area about 300 kg of NPK fertilizer is commonly applied twice a month. In Indonesia farmers apply 150-300 kg/ha of urea after each harvest. Cultivation is terminated in the event of low temperatures in "winter" (in China, Taiwan and Hong Kong), flowering (in Thailand), or serious disease, pest or weed problems.
Diseases and pests
Owing to the short growing period of one crop of upland kangkong, diseases and pests do not cause much harm. Where ratooning is practised they can become a nuisance. White rust (Albugo candida) is reported from Thailand, Indonesia, Malaysia, Singapore and Hong Kong. Damping-off of seedlings caused by Pythium sp. may occur, and occasionally Cercospora leaf-spot. Root knot nematodes (Meloidogyne spp.) may become troublesome in ratoon cropping. Caterpillars of Spodoptera litura and Diacrisia strigatula and aphids may cause serious damage. Chemical control is a general practice, regardless of the hazards of toxication.
Consumers have specific preferences with regard to the quality of the product, e.g. number of leaves, stem length, percentage of fibre, taste.
- Upland cultivation. Harvest takes place from 20-50 days after sowing. In Thailand, Malaysia, Singapore, Taiwan and China, uprooting the plants 20-30 days after sowing is common practice. The stems of these seedlings are big and tender but crisp. Ratooning is only practised in home gardens.
- Paddy-field cultivation. Harvesting is done by cutting young shoots one to two months after planting, and subsequently at regular intervals. In Indonesia and the Philippines plants are cut about 5-10 cm above ground level every 4-6 weeks. The stems are thinner but more fibrous and tough when compared to upland kangkong.
Under upland cultivation, yields per crop range from 7-30 t/ha of fresh produce, depending largely on the cultivation period. Yields per year are up to 400 t/ha of fresh produce. Under wet cultivation, yields are difficult to compare because cultivation periods differ greatly. Annual yields of 24-100 t/ha are reported. For floating kangkong an annual production of 90 t/ha of fresh produce is reported for Thailand.
Handling after harvest
Shoots of paddy-field kangkong are tied into bundles and transported to the market. Entire plants of upland kangkong are washed or wetted and sometimes wrapped in plastic to prevent wilting. In Taiwan, bundles are packed in layers of approximately 15 cm in bamboo crates. Crushed ice is placed between the layers, sandwiched between sheets of banana leaves.
Germplasm is available at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan and at national research institutes in South-East Asia. A collection of at least 50 landraces of kangkong is available at the Kasetsart University in Bangkok (Thailand).
Not much breeding work has been carried out on the crop in South-East Asia. A seed company in Thailand has selected some superior cultivars.
Gradually the seed-propagated upland kangkong will become more important at the expense of the vegetatively propagated paddy-field kangkong. Research should focus on the improvement of cultural practices, especially regarding fertilizer application and control of insect damage. Breeding efforts should concentrate on obtaining productive cultivars with acceptable quality that are well adapted to specific environments and resistant to white rust.
- Cornelis, J., Nugteren, J.A. & Westphal, E., 1985. Kangkong (Ipomoea aquatica Forssk.): an important leaf vegetable in South-East Asia. Review Article. Abstracts on Tropical Agriculture 10 (4): 9-21.
- Edie, H.H. & Ho, B.W.C., 1969. Ipomoea aquatica as a vegetable crop in Hong Kong. Economic Botany 23(1): 32-36.
- Linnemann, A.R., Louwen, J.M., Straver, G.H.M.B. & Westphal, E., 1986. Influence of nitrogen on sown and ratooned upland kangkong (Ipomoea aquatica Forssk.) at two planting densities. Netherlands Journal of Agricultural Science 34: 15-23.
- Burkill, I.H., 1966. A dictionary of the economic products of the Malay Peninsula. Revised reprint. 2 volumes. Ministry of Agriculture and Co-operatives, Kuala Lumpur, Malaysia. Vol. 1 (A-H) pp. 1-1240, Vol. 2 (I-Z) pp. 1241-2444.
215, 407, 647, 786, 914, 1014, 1026, 1070. medicinals
- E. Westphal
- Anna L.H. Dibiyantoro & G.H. Schmelzer