Indigofera hirsuta L.

Leguminosae

Common names

Hairy indigo.

An erect or spreading annual, up to 1 .5 m tall but generally shorter. Stems cylindrical or slightly ridged, densely clothed with long, fine, spreading, grey or reddish-brown pubescence. Stipules linear, setaceous, up to 1 cm long. Five to seven leaflets, occasionally nine, elliptical-oblong, up to 40 mm long and 25 mm wide, the terminal one rather longer than the lateral, pilose on both surfaces. Inflorescence a dense, many-flowered raceme, hirsute, 20 to 30 cm long including a peduncle more than 25 mm long. Bracts linear-lanceolate, up to 25 mm long. Pedicels around 1 mm long, reflexed in fruit. Calyx stiff, brown and hirsute, about 4 mm long, divided almost to the base into linear, setaceous lobes. Corolla white pubescent outside, brick-red or rose inside. Pods straight, rather tetragonal, with well-developed sutures, 12 to 20 mm long about 2 mm wide, thickly hirsute; many of the hairs, especially the dorsal ones, usually brown. Six to nine seeds, cuboid, angular, strongly pitted (Gillett, Polhill and Verdcourt, 1971).

Hairy indigo occurs naturally from Senegal to the Sudan and the Congo, Zambia, Mozambique, Angola and Madagascar in Africa; also natural in southern Asia, northern Australia and Queensland, Australia. It has been naturalized in parts of tropical America.

A summer-growing annual with strains of varying maturity available.

Grown from sea level to 1 350 m in Africa.

Occurs naturally in areas with 900 to 1 700 mm annual rainfall, rarely less.

Tolerates soils of low pH and fertility, and thus can be useful for soil improvement. It is, however, best adapted to moderately acidic soils and fertile sandy loams, thriving with little lime.

The native strains in Queensland nodulate with the cowpea cross-inoculation group (Bowen, 1956), while in Florida, United States, no inoculation is necessary (Whyte, Nilsson-Leissner and Trumble, 1953).

A free-seeding annual without specific Rhizobium requirements, hairy indigo can naturalize readily in suitable habitats.

McKee (1952) recommends planting from March to late May, but preferably earlier, at 3 to 5 kg. of seed per hectare when drilled in close rows and 6 to 10 kg./ha when broadcast on a well-firmed seed bed, the smaller amount for seed crops, the higher figures for hay or green manure.

440 000.

Being well-adapted to low-fertility soils, I. hirsuta has not shown major responses to applied fertilizer. In Panama, Silvey and Carlisle (1972) obtained no dry-matter-yield response to the application of up to 30 kg./ ha Zn or up to 100 kg./ha P, although forage content of both elements was increased. Liming at up to 2 000 kg./ha Ca depressed extractable Zn and P in the soil and increased forage yield but not crown or root yields.

In Florida, it has been estimated that the presence of hairy indigo in mixtures is equivalent to the application of 126 kg./ha N/year on pure grass pastures (Kalmbacher, Hodge and Martin, 1980).

Kalmbacher, Hodge and Martin (1980) found that plant height at initial harvest was important: regrowth was inhibited at taller heights because regenerative axillary buds were removed during harvesting. Recovery after cutting was also slow at Carimagua, Colombia, (CIAT, 1978) .

In Florida, a mixture of I. hirsuta and pangola grass yielded 4.88 t/ha dry matter, while alone the pangola grass yielded only 3.31 t/ha. Setaria sphacelata yield increased from 2.24 t/ha DM alone to 4.52 t/ ha when mixed with I. hirsuta but there was no increase in yield when I. hirsuta was added to a Paspalum notatum pasture. The I. hirsuta mixtures however yielded less than the same grasses with other legumes (Kretschmer, 1970).

One of the first uses for I. hirsuta in Florida was hay and silage production, but the hay must be made early in the season as the stems become coarse and woody with age. The aftermath from such an early cut can then be grazed. Silage made from it satisfies only maintenance requirements and was not readily eaten (Catchpoole and Henzell, 1971).

Dougall and Bogdan (1966) analysed I. hirsuta forage as containing 23.8 percent crude protein, 2.0 percent ether extract, 15.2 percent crude fibre, 46.8 percent nitrogen-free extract, 1.88 percent calcium and 0.37 percent phosphorus, but Kalmbacher et al. (1980) showed that crude protein and in vitro organic matter digestibility are greatly influenced by time of sampling, declining rapidly as the plant material ages. Early cut material contained 24 percent crude protein.

Early references such as Bailey (1906) refer to suspected poisoning of stock, but these suspicions apparently have not been sustained.

1. hirsuta was initially regarded as somewhat difficult to harvest for seed because the plant dries slowly after the seed matures (McKee, 1952). Modern, high-powered headers should handle it readily. McKee (1952) recommends mowing and drying in the windrow before threshing, although he believed that a header could be used on thin, short stands.

A good seed producer.

Seed was first offered for sale in Florida in 1945 from work begun at Gainesville in 1931. Two distinct types were initially used, one a large, late-maturing strain and the other a smaller type that matured a month earlier (McKee, 1952). No cultivar name has been noted for either line.

Free-seeding and regenerating readily each year, hairy indigo's tolerance of low soil pH and fertility coupled with its resistance to root knot nematode make it an attractive legume for poor sandy soils in Florida.

A rather low-quality forage, the quality of which declines even further as growth advances.

McKee (1952); Kalmbacher, Hodges and Martin (1980).

Grown as far south as 30°S in Argentina and as far north as southern Georgia (c. 32°N) in the United States.

Resistant to root knot nematode (Meloidogyne spp.) and most insects and diseases.

In Taiwan, I. hirsuta was one of the plants that Wang (1961) grew under natural day lengths of from 10 hr 19 min in mid-January to 13 hr 42 min in mid June, photoperiods approximately three hours longer and shorter respectively than normal. It responded to short photoperiods by shortening the period to flowering. During flowering, vegetative growth increased.

A fine, firm, weed-free, well-prepared seed bed is ideal. Like most free-seeding annuals, however, hairy indigo should be susceptible to more simple methods of introduction into pasture situations.