Perennial soybean, glycine, wild soya bean, rhodesian kudzu, Cooper glycine [English]; soja pérenne [French]; soja perenne forrajera, soja forrajera [Spanish]; soja-perene [Portuguese]; fundo fundo [Tanzania]; thua peelenian soibean [Thai]; 爪哇大豆 [Chinese]

Neonotonia wightii (Wight & Arn.) J.A. Lackey [Fabaceae]

Glycine javanica auct., Glycine javanica L. var. paniculata Hauman, Glycine albidiflora De Wild., Glycine claessensii De Wild., Glycine javanica sensu auct., Glycine javanica L. var. claessensii (De Wild.) Hauman, Glycine javanica L. var. longicauda (Schweinf.) Baker, Glycine javanica L. subsp. micrantha (A. Rich.) F.J. Herm., Glycine javanica L. var. mearnsii (De Wild.) Hauman, Glycine longicauda Schweinf., Glycine mearnsii De Wild., Glycine micrantha A. Rich., Glycine moniliformis A. Rich., Glycine petitiana Hermann pro parte, Glycine pseudojavanica Taub., Glycine wightii (Wight & Arn.) Verdc. var. longicauda (Schweinf.) Verdc., Glycine wightii (Wight & Arn.) Verdc. subsp. petitiana (A. Rich.) Verdc. var. mearnsii (De Wild.) Verdc., Glycine wightii (Wight & Arn.) Verdc. subsp. petitiana (A. Rich.) Verdc., Glycine wightii (Wight & Arn.) Verdc. subsp. pseudojavanica (Taub.) Verdc., Glycine wightii (Wight & Arn.) Verdc. subsp. wightii, Johnia wightii (Wight & Arn.) Wight & Arn., Johnia petitiana A. Rich. (USDA, 2011)

Perennial soybean (Neonotonia wightii (Wight & Arn.) J.A. Lackey) is a trailing, climbing or twining herbaceous legume. It has a deep taproot and twining stems, 2.5 cm in diameter, woody at the base and then slender and well branched. The plant produces runners that root from the nodes. The stems can grow up to 10 m with adequate supporting species (trees). They can regrow from the underground crown if the plant has been damaged or if it has been grazed. The compound leaves bear 3 ovate and hairy leaflets, 5-10 cm long and 3-6 cm broad. The inflorescence is a 4 to 30 cm long raceme with clusters of white or violet flowers. In some varieties, the flowers turn yellow or orange-yellow at senescence. The fruits are hairy, linear-oblong, 1-4 cm long and about 3 mm broad. The pods contain 3-8 oblong seeds, shattering at maturity. Seeds vary in size, shape and colour, depending on variety (FAO, 2011).

Perennial soybean is mainly used as pasture or hay and is valued for its drought resistance and high yields (Pengelly et al., 1992; Göhl, 1982). It does well with companion grasses (Göhl, 1982).

Perennial soybean originates from Africa and is widespread in the East Indies, tropical Asia and East, Central and Southern Africa (FAO, 2011). It has been introduced to many islands of the South Pacific, including the highlands of Papua New Guinea. It can also be found in Cuba, Brazil and in subtropical Australia (Ecoport, 2011; Cook et al., 2005). Perennial soybean is a summer-growing species which is found in grassland, in shaded situations in bushland, thicket and woodland or in degraded areas from sea level up to an altitude of 3000 m in tropical regions (Pengelly et al., 1992). It grows best at the end of the rainy season and during the dry season, as it is a quite drought-tolerant species. It is a suitable legume in semi-arid areas because it is able to survive dry spells and recover once favourable conditions resume (FAO, 2011; Mero et al., 1997).

Perennial soybean grows best when day temperatures range from 22 to 27°C and with average annual rainfall between 750 and 1500 mm. It cannot stand much higher rainfall but is tolerant to drought. Perennial soybean prefers well-drained soils but has some tolerance of waterlogging and of short periods of flooding. It can also survive some frost periods even if frost causes leaf shedding (FAO, 2011; Cook et al., 2005).

Perennial soybean favours deep, heavy, well-drained and basalt-derived soils. It prefers soil pH above 6.5 but can be grown on pH 6 and even lower (5.8) provided that lime is added to the soil. Lime input prevents manganese toxicity under acidic conditions (FAO, 2011; Njarui et al., 2003). In neutral conditions, perennial soybean had good resistance to pests and diseases (Paterson et al., 1981). Perennial soybean is more tolerant to salinity than other tropical legumes. However, salt may have a depressive effect on nodulation (Göhl, 1982). Once well established, perennial soybean is also tolerant of fire and produces green shoots after burning (Cook et al., 2005).

Yields

Perennial soybean yields vary between 3.85 and 10 tons DM/ha, depending on environmental conditions (Cook et al., 2005). Its growth is greater during the rainy season than during the dry one. For example, in Cuba, dry matter availability in a pedestal system (see Pasture below) varied from 33 kg/animal/day (rainy season) to 25 kg/animal/day (dry season), resulting in a higher milk production in dairy cows grazing Neonotonia wightii during the rainy season (Sanchez et al., 2006).

Pasture

Once well established, Neonotonia wightii should not be left ungrazed as it reduces production. It should be cut between 3.75 and 5 cm every 8 to 10 weeks (Cook et al., 2005). In mixed sown pastures (Guinea grass/perennial soybean), grazing can start 7-8 weeks after sowing but only long enough to remove the grass canopy, and livestock should not be allowed to graze the legume seedlings. Once perennial soybean is well developed it can be grazed in winter and spring. Grazing must stop at the beginning of the rainy season so that the leaves can grow (FAO, 2011).

Perennial soybean should be grazed rotationally during the warm wet months and continuously during winter (FAO, 2011). It is possible to manage grazing in order to get most of the plant at a desired period. For example, light grazing during summer will prepare winter grazing; if early summer grazing is desired, the stand should be heavily grazed during the previous summer and then left to rest during autumn. If frost occurs, the stand should be grazed immediately because palatability rapidly drops after frost (Cook et al., 2005).

In Cuba, Neonotonia wightii is used in a rotational grazing system called "pedestales", where legumes grow on wire trellises and are intercropped with strips of grasses (Pacheco, 2007).

Hay and silage

Perennial soybean should be cut at the flowering stage, dried down to 12% moisture and then stored as hay. In mixed stands, perennial soybean and grass (such as Digitaria eriantha, Pennisetum purpureum and Megathyrsus maximus) can be ensiled together. Molasses of fodder sugarcane can be added to the silage (FAO, 2011).

Standover or deferred feed

Neonotonia wightii is a valuable deferred feed but cannot withstand frost. In Brazil, it is a good winter forage, and in Australia it maintained 2.5 cows per ha in good condition during the winter (Cook et al., 2005; Partridge, 2003).

Invasive species

Though Neonotonia wightii was first assessed for land restoration due to its protective effect against erosion, it is now considered to be an invasive species in Hawaii as it may smother more desirable species (US Forest Service, 2011; Ziegler et al., 2000).

Soil improver, pests and weed controller

Neonotonia wightii is an N-fixing legume, and as such enhances the N status of the soil. It can help restore degraded soils very quickly, prevent erosion and suppress weeds. For example, in Cuba, it has been used in organic citrus plantations (Alföldi et al., 2002). Perennial soybean may have a double protective effect in banana plantations: its deep taproot explores the deepest parts of the soil while banana roots develop horizontally. There is thus no competition for soil nutrients and perennial soybean provides N to the banana plants. As a cover crop, perennial soybean prevents banana plantations from being invaded by weeds and it might alleviate nematode attacks (Risède et al., 2010).

Fallow crop, cover crop and intercrop

Neonotonia wightii has been used in small areas of Papua New Guinea as a fallow crop in abandoned gardens, as a cover crop and for woody weed control in overgrazed pastures (Pengelly et al., 1992). Perennial soybean may also be intercropped with cereals in semi-arid areas since it shows good perennation and regeneration. Its moderate growth during the first year lets the cereal grow without heavy competition (Njarui, 1988). Perennial soybean has also been used in mixed pasture with green panic (Megathyrsus maximus var. pubiglumis) in order to restore soil fertility after continuous maize cropping (Partridge, 2003).

Neonotonia wightii forage contains 14-20% DM of crude protein, which is lower than for other tropical legumes forage such as leucaena or gliricidia (Feedipedia, 2011). It decreases with the stage of growth: in New South Wales (Australia), crude protein varied from 18.9% DM when leafy to 12.9% DM when seeded and frosted (Holder, 1967). The fibre content is relatively high (crude fibre 26-35% DM; NDF 45-60%; ADF 33-40%; ADL 8-10%; Feedipedia, 2011). Fibre and lignin content increases with age while pectin decreases (Vera et al., 1989). While Neonotonia wightii is not one of the most nutritious legumes, it is often used to improve grass pastures, as the dietary increase in crude protein increases intake and the nutritive value of the diet.

Perennial soybean contains some oestrogenic substances but no breeding troubles in livestock have been reported (FAO, 2011).

Palatability

Neonotonia wightii has a good palatability. In Brazil, its palatability improved as the plant became more vigorous in mid-season and was maintained into the autumn (Lychatchynsky et al., 1968 cited by FAO, 2011). Perennial soybean was found to be as palatable as other legumes, including Stylosanthes guianensis, Centrosema molle, Pueraria phaseoloides and Macroptilium atropurpureum (Souto et al., 1975), though the latter was found more palatable in one trial (Kretschmer et al., 2001).

Digestibility

The digestibility of Neonotonia wightii compares favourably with that of alfalfa and other legumes forages (FAO, 2011). Organic matter digestibility is generally in the 55-65% range (Mero et al., 1998a; Mero et al., 1998b; Ribeiro et al., 1980a; Ribeiro et al., 1980b). It has been estimated that the digestibility of perennial soybean was about 10 units lower than that of a temperate legume at an equivalent stage of growth (Holder, 1967).

Digestibility decreases with the stage of growth. The DM digestibility of fresh forage measured in cattle varied from 62% when leafy to 56% DM when seeded. The digestibility of crude protein reached 80% in young forage (Holder, 1967). In sheep fed Neonotonia wightii hay, DM and protein digestibility decreased from 53 to 44% and from 66 to 52%, respectively, between pre-bloom (71 d) and late flowering (112 d) (Vera et al., 1989).

Dairy cows

In Cuba, cows grazing pastures of Neonotonia wightii and Pennisetum purpureum yielded significantly more than cows grazing grass (Brachiaria mutica or Pennisetum purpureum/Digitaria eriantha) (10.6 vs. 8.1 and 7.0 kg milk, respectively) (Perez Infante et al., 1979). In Bolivia, access by dairy cows and their calves to legume pasture (Neonotonia wightii, Macrotyloma axillare and Stylosanthes guianensis) during the dry season increased milk yield and milk fat percentage. Calf growth was poor but tended to improve with access to legumes (Paterson et al., 1983).

Growing cattle

Most of the feeding trials with Neonotonia wightii concern growing cattle and the benefits of its association with grasses. These trials (see table below for a summary) usually demonstrate the superiority of grass/legume mixtures containing Neonotonia wightii:

Sheep

In Hawaii, intake by adult sheep of a dried 1:3 mixture of Neonotonia wightii and Guinea grass (Megathyrsus maximus) was around twice that of pure Guinea grass. The grass-legume mixture also had a better nutritive value than grass alone (Campbell et al., 1980).

Goats

In Kenya, male kids that lost weight when fed on natural pastures (Pennisetum purpureum and other grasses) had positive weight gains when supplemented with legume forages (fresh, chopped, 30% of the feed requirement). The gain with Neonotonia wightii (16.4 g/d) was higher than with Macroptilium atropurpureum (4.0 g/d) but much lower than with Leucanea leucocephala (31.3 g/d) (Njarui et al., 2003).

When goats were fed perennial soybean grass hay to excess, a reduction occured in the lignin intake, but not in the other cell wall components (da Silva et al., 1999).

Ducks

Ducks fed Neonotonia wightii forage consumed 26.5 g/d (DM). It was less consumed than Leucaena leucocephala (Tapia et al., 1999).

Perennial soybean is a valuable forage for rabbits and is readily eaten. Perennial soybean hay was for example the reference forage in a study of other tropical forages included at 13% to 23% in feeding blocks (Nouel et al., 2003). Perennial soybean is both a source of protein and a source of fibre, and the hay could replace 100% of alfalfa meal in balanced diets (38% of the diet) without altering rabbit growth and slaughter performance (Crespi et al., 1992).

Observed values for DM digestibility vary widely, between 34% (Ferreira et al., 1997) and 65% (Nouel et al., 2003). The in vitro dry matter digestibility of perennial soybean obtained through incubation with rabbit caecal content was very high at 93% (Dihigo et al., 2004).

• Forest and Kim Starr
• Forest and Kim Starr
• Forest and Kim Starr