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Sorghum x drummondii (Steud.)
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Gramineae Synonyms
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Author: L.’t Mannetje |
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Common names Sudan grass (En). Pasto Sudan (Sp). Philippines: batag (Tagalog), bukakau (Ilokano), layagah (Sulu). Thailand: ya-sudan. Origin and geographic distribution Sudan grass is a segregate from a natural hybrid between S. bicolor (L.) Moench and S. arundinaceum (Desv.) Stapf. This hybrid combination is responsible for several other 'species' which are, however, unstable, and revert to one or other of their parental types. They have all been included in the binomial S. x drummondii. The hybrid originated in the region from southern Egypt to the Sudan. It was introduced to the United States in 1909 and rapidly became popular as a forage, later being evaluated and sown in other regions with warm and dry growing seasons. It is also widely used in Russia and eastern Europe. It is commonly used as a parent in a wide range of inter-specific F1 hybrids in which S. bicolor, grain sorghum, is the alternative parent. Examples of such hybrids are 'Sudax', 'Zulu' and 'Bantu' (Hacker 1992). Annual with erect stems to 3 m tall, 3-9 mm thick. Leaf-blade lanceolate, 30-60 cm x 8-15 mm. Inflorescence an open pyramidal panicle with secondary and sometimes tertiary branches which end in short fragile racemes, which do not readily break up at maturity; spikelets paired; sessile spikelet 6-7 mm long; glumes loosely hairy, shiny and almost hairless when mature; upper lemma with an awn up to 16 mm long; pedicelled spikelet about as long as the sessile spikelet, but narrower. Caryopsis variable, enclosed by the glumes. A proportion of the many 'cultivars' that are marketed around the world as Sudan grass are, in fact, hybrids with other species. There are relatively few cultivars available within S. x drummondii as such, but considerable numbers of open-pollinated and F1 hybrids have been developed. Examples, and their parentage, are: 'Tift' (Sudan grass x 'Leoti' sweet sorghum) x Sudan grass; 'Piper' ('Tift' x Sudan grass); 'Greenleaf' ('Leoti' sweet sorghum x Sudan grass); 'Lahoma' (Sudan grass x 'Leoti' sweet sorghum); 'Sucro'(perennial) (S. x almum x perennial sweet Sudan grass); 'Sudax'(F1) (male sterile grain sorghum x Sudan grass); 'Zulu'(F1) (male sterile grain sorghum x 'Greenleaf') (see above); 'Bantu'(F1) (male sterile grain sorghum x 'Piper') (Hacker 1992). Use Sudan grass is used as forage for ruminants; it can be grazed or utilized in cut-and-carry forages, as hay or silage for ruminants. Properties Nitrogen concentrations can be as high as 3%, although levels fall with increasing maturity. Young leaf blades may approach 75% dry matter digestibility, while older leaves may be only 50 to 60% digestible and culms may be as low as 30 to 50% digestible. Brown midrib mutant inherited characters in some sorghum cultivars have reduced NDF, ADF and hemicellulose concentrations, and greater apparent digestibility (Hacker 1992, Fribourg 2000).There are 90-120 seeds/g. Toxicity In common with other sorghum species, young herbage of sudan grass can accumulate high levels of HCN which may lead to prussic acid poisoning in livestock. The HCN potential varies greatly among cultivars. The HCN potential can range from zero to several hundred parts per million on a fresh weight basis. This is rarely a serious problem in sudan grass, except where high levels of N fertilizer have been applied or where it is wilted. However, adequate phosphate status helps to minimize HCN toxicity. Prussic acid poisoning is considered to be less of a problem with Sudan grass than it is with either fodder sorghum or sorghum-Sudan hybrids (Hacker 1992; Fribourg 2000; Lucy 2000). Nitrate poisoning may result from the ingestion of sudan grass containing high concentrations of nitrate N in plants that were fertilized with high rates of N and subsequent slow growth. Sorghum species and cultivars should not be used with horses, which may develop cystitis, an inflammation of the bladder. This condition results in urinary disorders and lack of coordination of hind legs, and can be severe in some cases (Fribourg 2000). Use of sulphur blocks (10 to 12% S) is highly recommended when grazing forage sorghums. These can substantially improve weight gains, and also help reduce the risk of prussic acid poisoning. Ecology Sudan grass, is suited to warm conditions with low humidity and an average annual rainfall of 600-900 mm. It is not adapted to the humid tropics and sensitive to frost. It is intolerant of waterlogging but has reasonable tolerance of salinity. Flowering in Sudan grass is to some extent photoperiod-sensitive, but in the tropics it flowers freely. Soil requirements Sudan grass requires fertile soils of medium to heavy texture, but will respond on light soils to irrigation and fertilizer. Recommended fertilizer rates are 80 to 100 kg N/ha and 125-250 kg/ha superphosphate before planting, followed by 50 kg N/ha after grazing. Propagation and planting Sudan grass should be sown in a well-prepared seed-bed not deeper than 2.5 cm, at the start of the rainy season, when soil temperatures are around 15° C and rising for quick, even germination. Seed can be drilled at 8-12 kg/ha in rows 25-50 cm apart (wider in drier climates) or broadcast at 12-16 kg/ha. It is normally grown as a pure crop, although companion legumes such as Glycine max and Vigna unguiculata have been used. It responds well to irrigation in dry climates. Relatively low levels of fertilizer are normally used, but it responds to N, P and K fertilizers where these nutrients are deficient in the soil (Hacker 1992). Growth and development Seedlings emerge 5-6 days after sowing. Best time for grazing is when the crop is around 80 to 100 cm in height. Diseases and pests Cultivars differ in resistance to leaf diseases. These diseases are of greater concern where the crop is grown under conditions of higher humidity and rainfall than it is normally suited to. Many species of insects and nematodes attack sudan grass. A number of rusts, such as Puccinia purpurea infect forage sorghums (Fribourg 2000). Grazing crops need to be carefully managed to avoid problems with the development of the sorghum ergot fungus (Claviceps sp.) in flowering crops. Forage sorghums should be grazed or cut before flowering in order to prevent the production of fungus spores. This will avoid toxicity problems in grazing animals (Lucy 2000). Performance Sudan grass may be grazed, chopped and fed directly, or made into hay or silage. As stems are thin, compared with the perennial sorghum species, it dries quickly, which is an advantage when hay-making. For best regrowth, the crop should not be grazed lower than 15 cm. Rotational grazing is preferred for better utilization or the forage. Dry matter yields of 12 – 25 t/ha can be obtained. Sudan grass is very palatable to livestock so the level of utilization is high and cattle are reported to consume 80% of the forage at panicle emergence (Hacker 1992). Feedlot rations with 50 to 65% sorghum forage have been used successfully to fatten steers and lambs. Rations with a high content of sorghum forage must be supplemented with protein, phosphorus and other minerals (Fribourg 2000). A supplement of 10 g S/day resulted in increased milk production, in solids content and especially in protein, but butterfat content was lower (Stobbs and Wheeler 1978). Generally, liveweight gains on forage sorghum vary between 0.6 to 1 kg per head per day. As the racemes do not break up easily, seed production (ca. 500 kg/ha) of Sudan grass is easier than it is with many tropical grasses, even though flowering within individual plants is poorly synchronized. Links
Fribourg H. (2000); Hacker J.B. (1992); Lucy M. (2000); Stobbs T.H. and Wheeler J.L. (1978) |