Indigofera hirsuta (PROSEA)
- Protologue: Sp. pl.: 751 (1753).
- Family: Leguminosae - Papilionoideae
- Chromosome number: 2n= 16
Indigofera indica Miller (1768), I. ferruginea Schum. & Thonn. (1829), I. angustifolia Blanco (1837).
- Hairy indigo (En). Rough hairy indigo (Am). Indigotier hérissé (Fr)
- Indonesia: tom-toman, jukut lulut (Java), tebawang amjak (Sulawesi)
- Malaysia: cermai burong
- Philippines: tayom (Iloko), tagum (Bisaya), tina-tinaan (Tagalog)
- Papua New Guinea: tildjil, wiereka
- Thailand: khram-khon (northern)
- Vietnam: cây cỏ chàm, cây sục sạc ma, chàm lông.
Origin and geographic distribution
I. hirsuta is native to Asia and Africa. It was cultivated as a green manure in Bogor in the 19th Century and was first tried as such in Malaysia in 1913. It was introduced into the United States in 1908 and proved suitable for cultivation in the coastal regions of Florida and Texas. It is now cultivated throughout the tropics.
I. hirsuta is a valuable green manure and cover crop, used especially in tea, coffee and rubber plantations. Research interest in hairy indigo as a cover crop or green manure in South-East Asia has been limited in recent years. In Florida it is often considered a weed in row-crop fields, but in citrus plantations it is grown as a cover crop. It is used especially where erosion control is important.
It is grown as an annual fodder in Florida and Brazil and in mixtures with grasses as a forage crop. A decoction made from the leaves is used against stomach problems in the Philippines, and against yaws in Ghana. In West Africa it has occasionally been used as a dye.
Per 100 g dry matter, leaves contain: N 2.14 g, P 0.12 g, K 1.53 g, and Ca 3.00 g. Hay cut at the flowering stage contains per 100 g: moisture 10.7 g, crude protein 13.7 g, crude fat 1.4 g, N-free extract 46.0 g, fibre 21.0 g, ash 7.2 g; digestibility coefficients are: dry matter 62.5%, protein 67.0%, fat 61.0%, N-free extract 67.0%, fibre 53.5%. Cattle do not graze hairy indigo readily, but intake is good after adaptation. It is somewhat toxic and should not constitute a large proportion of the diet. Cattle grazing on it for extended periods of humid weather may develop sores on their feet and legs. It is believed that the hairs of the plants irritate their wet skin.
The weight of 1000 seeds is 1.5-2.5 g.
Annual herb or subshrub, up to 1.5 m tall, covered with conspicuous brown hairs, which are biramous and spreading with very unequally long arms, looking almost simple. Branches erect, striate, becoming woody at seed maturity. Leaves imparipinnate; stipules narrowly triangular to linear, 10-12 mm long; petiole 2-5 cm long; rachis up to 9 cm long; stipels 1-2 mm; petiolule 1.5-3 mm long; leaflets 5-11, opposite, elliptical to obovate, terminal one 2.5-3.5(-6) cm × 1-2(-3) cm, lateral ones 1.5-3 cm × 0.7-1.5 cm, base cuneate, apex rounded, mucronate, hairy to strigose on both surfaces, veins distinct, main vein brown. Inflorescence a densely flowered raceme, (3-)10-30 cm long; bracts linear-triangular, about 4 mm long, caducous; peduncle 3 cm or longer; pedicel about 2 mm long; flowers up to 6 mm long; calyx about 4 mm long, with stiff brown hairs, divided almost to the base into linear, setaceous lobes; corolla red to pink; standard elliptical, 4-5 mm × 2-2.5 mm, emarginate at apex; white pubescent outside; wings 4-5 mm × 1.5 mm, hairy at upper margin; keel 4-5 mm × 1.2-1.5 mm, upper margin with hairs, lateral pocket 0.7 mm long; staminal tube 4.5 mm long; anthers 0.4 mm long; ovary hairy with 6-9 ovules. Fruit a reflexed, straight pod, rounded to tetragonal in cross-section, 1-2 cm × 1-2.5 mm, with well developed sutures, and with long spreading hairs, dehiscent, (4-)6-9-seeded, endocarp blotched. Seed cuboid, 1 mm long, brown, distincly pitted.
Growth and development
Early growth of seedlings is very slow. Weeding is therefore only possible after 4-6 weeks, when plantlets can be distinguished from weeds. Under suitable conditions the plants reach a height of 30 cm after about 50 days, 60 cm after 65 days and 90 cm after about 80 days. In Sri Lanka, I. hirsuta flowers and fruits from September to February and in the United States it flowers late in the growing season, producing a good green manure or forage crop before seed maturation. Pollination is by insects. Hairy indigo fixes atmospheric nitrogen symbiotically with cowpea-type rhizobium.
Other botanical information
I. astragalina DC. is sometimes included in I. hirsuta , forming a single, polymorphic species. I. astragalina usually has more leaflets than I. hirsuta , often whitish hairs, a shorter peduncle and paler flowers. It occurs in the Sudano-Sahel zone, south-eastern Africa, Pakistan, India, Sri Lanka and Burma (Myanmar). Where both species occur in the same region, I. hirsuta occupies the wetter areas. Genetic diversity in hairy indigo is greatest in Africa, from where cultivars have been reported showing tolerance to diseases, pests, weeds, low pH, poor soil, and shade.
I. hirsuta occurs as a weed in cultivated and waste areas, in grassland, savanna, dry and deciduous forest, on river banks and beaches, at 0-1500 m altitude. It requires an annual rainfall of 900-2500 mm and an annual mean temperature of 15-28 °C. It does not tolerate frost. A dry season stimulates flowering and seed production. Although generally fairly tolerant to shade, growth under heavy shade in an established stand of pine trees in Costa Rica was poor. Hairy indigo is tolerant to poor soil conditions, growing well on moderately poor, sandy soils with low pH, and on slopes. It requires moderately to well-drained soils with a pH of 5-8 and is intolerant of waterlogging.
Propagation and planting
I. hirsuta is propagated by seed. Germination percentage is often low, but can be improved by hot water treatment (70-80 °C for 20-30 minutes). Seed of early selections is smaller than that of later ones. In Florida, hairy indigo is sown from early to late spring, with early sowing being preferred. When drilled in closely spaced rows a seeding rate of 3-5 kg/ha is used; when broadcast in a well firmed seed-bed 6-10 kg/ha of seed is needed. Lower rates are recommended for seed production. Seed should preferably be sown at a depth of 1 cm, but may be broadcast without any follow-up soil cultivation. Trampling by cattle and rain will result in the seed being covered sufficiently. Seed germinates after 7-9 days. Under grazing in Florida, hairy indigo is a self-regenerating annual, even in fields that are burned or disked.
In permanent, mixed pastures, cattle need not be removed during the period of seed development. Reducing grazing intensity is sufficient to produce enough seed for a volunteer crop. Disturbing the soil superficially results in a better volunteer crop.
In the United States, weeding and earthing up is done 1-1.5 months after planting and again 1 month later. Cover crops in tree-crop plantations are slashed at regular intervals. Slashing and lopping is tolerated well. Phosphate and potash applications increase growth, recommended amounts in Florida are: P2O530-70 kg/ha and K2O 30-50 kg/ha. Hairy indigo can be relay-planted in maize. When planted 40 days after germination of maize, it produces a dense soil cover soon after the maize harvest, yielding 4-5 t dry matter per ha containing about 100 kg of nitrogen.
Established mixed grasslands should be grazed closely at the beginning of the growing season until I. hirsuta germinates and establishes itself.
Diseases and pests
I. hirsuta exhibits some tolerance to most diseases and pests. The following fungi have been reported as occurring on hairy indigo but without causing serious dieseases: Colletotrichum dematium , Corticium solani , Rhizoctonia solani , and Sclerotium rolfsii . It has shown extensive tolerance to root-knot and sting nematodes. Experiments indicate that hairy indigo in a rotation markedly reduces the numbers of several Meloidogyne spp. Genetic variation in tolerance and antagonistic effects to nematodes is considerable and should be further investigated.
I. hirsuta can be harvested as common hay crops with ordinary farm equipment. It should be cut early when 75-90 cm tall. If cut early when 20-25 cm tall before flowering, a second growth may be expected. The regrowth may then be used for grazing or hay. Grazing should be rotational, to prevent severe removal of leaves.
Seed can be harvested by cutting the infructescences by hand. Very large plants may be cut with a mowing machine, allowed to dry in windrows and threshed. Stands that are not too heavy can be combine harvested. Harvesting should be done when seed is mature, but before shattering. Seed set is abundant. In the United States seed of large-seeded strains matures in late autumn, while smaller-seeded strains mature 3-4 weeks earlier.
In Florida green matter yields of I. hirsuta average about 22 t/ha (13 t/ha dry matter) and in coconut plantations in India 10 t/ha. Seed yields average 100-300 kg/ha. No information is available on yields in South-East Asia. In Florida in mixed stands with pangola grass ( Digitaria eriantha Steudel) or Bahia grass ( Paspalum notatum Flueggé), annual dry matter yields of about 5.5 t/ha are obtained with an average crude protein content of about 10%. Forage yields were lower than those of mixtures with Desmodium intortum (Miller) Urban, D. heterocarpon (L.) DC. and Macroptilium atropurpureum (DC.) Urban.
A small germplasm collection of I. hirsuta is maintained by the United States Department of Agriculture in Florida and at the Southern Regional Plant Introduction Station, Griffin, Georgia.
Very little breeding work has been done in I. hirsuta . Early and late-maturing lines were developed in Florida in the early 1940s, but they no longer exist. New early ("FL-24") and late ("Fl-101") cultivars were released in 1988.
The strong ability to reseed itself and its development late in the season make I. hirsuta a good green manure in annual crops. Further selection work is needed to investigate its potential to produce high organic matter yields. Its efficacy to reduce nematode infestation needs further investigation.
- Backer, C.A. & Bakhuizen van den Brink, R.C., 1963. Flora of Java. Vol. 1. Noordhoff, Groningen, the Netherlands. p. 591.
- Baltensperger, D.D., French, E.C., Prine, G.M., Ruelke, O.C. & Quesenberry, K.H., 1985. Hairy indigo, a summer legume for Florida. University of Florida, Gainesville, United States. 11 pp.
- De Kort, I. & Thijsse, G., 1984. A revision of Indigofera in Southeast Asia. Blumea 30: 120-121.
- Kalmbacher, R.S., Mislevy, P. & Martin, F.D., 1981. Minerals in the forage of American jointvetch and hairy indigo as affected by harvest height. Proceedings of the Soil and Crop Science Society of Florida 40: 124-127.
- Perry, L.M., 1980. Medicinal plants of East and South-East Asia. Massachusetts Institute of Technology Press, Cambridge, Massachusetts, United States. p. 218.
- Rodríguez-Kabana, R., Robertson, D.G., Wells, L. & Young, R.W., 1988. Hairy indigo for the management of Meloidogyne arenaria in peanut. Nematropica 18: 137-142.
- Sabiiti, E.N., 1980. Dry matter production and nutritive value of Indigofera hirsuta L. in Uganda. East African Agricultural and Forestry Journal 45: 296-303.