Sorghum xalmum (PROSEA)
Sorghum ×almum Parodi
- Protologue: Rev. Argent. Agron. 10: 361 (1943).
- Family: Gramineae
- Chromosome number: 2n= 40 (tetraploid)
- Columbus grass (En). Pasto colon, sorgo negro (Sp)
- Philippines: batag (Tagalog), gau (Ifugao)
- Thailand: ya-sokum.
Origin and geographic distribution
This species, first noted in Argentina, is considered to be a natural hybrid between S. halepense (L.) Pers. (Johnson grass) and S. bicolor (L.) Moench (grain sorghum). It has been introduced into some South-East Asian countries, notably Thailand, but is only used to a very limited extent.
Used as a forage for grazing by cattle, or less commonly for hay or silage, Columbus grass has now largely been replaced by the man-made hybrid cultivar "Silk". Columbus grass is mostly grown in pure stands.
Herbage of Columbus grass is of reasonably high quality and N concentrations in leaves can be over 3% if stands are adequately fertilized, although concentrations decrease as plants mature. It is palatable to cattle. Young herbage can accumulate dangerously high levels of HCN which may lead to prussic acid poisoning in livestock. Unlike its putative Johnson grass parent, it can be eradicated without difficulty when so desired.
Densely tufted perennial to about 3 m tall, producing short, thick, ascending terminal rhizomes. Leaf-blade flat, 30-100 cm × 15-40 mm. Inflorescence an open panicle 20-60 cm long, the lowermost branches in whorls of 4-9; spikelets in short fragile racemes, paired, the lower one 5-6.5 mm long, mostly with an awn about 1 cm long; glumes brown or black, completely covering the caryopsis at maturity.
Columbus grass may be distinguished from the widespread weed species S. halepense by its short ascending terminal rhizomes and its 5-6.5 mm long sessile spikelets. S. halepense has some rhizomes which arise from side buds and elongated and sessile spikelets 4.5-5mm long. Columbus grass cultivars are "Crooble" and "Nunbank" (Australia), "de Soto" (United States) and "Rietondale" (South Africa).
Columbus grass is well adapted to heavy clay soils and areas receiving 500-800 mm rainfall. It can tolerate drought and some salinity. Stands are not killed by mild frosts. It is intolerant of waterlogged soils.
Columbus grass is a reliable seed producer and is sown by seed, either broadcast at 20 kg/ha, or, preferably, drilled in rows 1 m apart at 5-7 kg/ha. Seedlings are vigorous and the species normally establishes without difficulty. Forage yields tend to be best in the season of sowing, and, although in exceptional circumstances it may persist for five years or more, mostly stands are ploughed out after the third year. Columbus grass seeds profusely and, as there is little loss from shedding, seed yields are high.
Columbus grass is commonly grown on more fertile soils and only low levels of N fertilization are required. On less fertile soils, the species responds well to applied N.
Colombus grass is susceptible to leaf blight ( Helminthosporium turcicum ) and leaf rusts ( Puccinia spp.).
Columbus grass is normally grazed, and topping to a height of 30-40 cm after grazing has been recommended. Stands of Columbus grass should not be grazed within 3 months of sowing nor should young regrowth be grazed, so as to avoid the risk of prussic acid poisoning. For hay or silage, stands should be cut at early flowering stage.
Dry matter yields as high as 19 t/ha per year have been recorded from two cuts. In farm practice, 4-10 t/ha per year can be expected, depending on rainfall and fertility. On an annual basis, liveweight gains of cattle of up to 0.5 kg/head per day can be expected, while weight gains of 1.3 kg/head per day have been recorded over shorter periods.
Genetic resources and breeding
Due to its probable hybrid origin and the large diversity of one of the parents, there is potential for extensive variation within S. × almum which may be exploited by the plant breeder. Columbus grass is predominantly cross-pollinating. It may be hybridized with Johnson grass, also a tetraploid, and with the diploids S. bicolor and S. × drummondii (Steud.) Millsp. & Chase. A limited germplasm collection is held by ATFGRC (CSIRO, Australia).
Columbus grass is used only to a very limited extent in South-East Asia and it is not anticipated that its usefulness will increase as better perennial sorghums are available.
- Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 264-269.
- Oram R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. p. 56.
- Silvey, M.W. & Ferraris, R., 1988. Sward productivity and seasonal animal production from perennial forage sorghums grazed at four stocking rates. CSIRO, Australia, Division of Tropical Crops and Pastures, Technical Memorandum No 56. 22 pp.
- Yates, J.J., Edye, L.A., Davies, J.G. & Haydock, K.P., 1964. Animal production from a Sorghum almum pasture in South-east Queensland. Australian Journal of Experimental Agriculture and Animal Husbandry 4: 326-335.