Basionym: Brachiaria ruziziensis R. Germ. and C.M. Evrard
Family: Poaceae (alt. Gramineae) subfamily: Panicoideae tribe: Paniceae subtribe: Melinidinae.
A tufted, spreading perennial grass forming a dense leafy cover. Culms decumbent, geniculately ascending, 50–100 cm long, 3–4 mm diameter, arising from short rhizomes, sometimes rooting from lower nodes; fertile culms to 1.5 m high. Leaf sheath longer than internode, loose, covered with dense tuberculate hairs; ligule a fringe of hairs; leaf-blades lanceolate to oblong lanceolate, contracted at base, tapering to an acute apex, 10–25 cm long, (6–) 11–15 mm wide, upper and lower surfaces densely villose with erect hairs, margins cartilaginous and slightly scabrous. Inflorescence a panicle comprising (3–) 5–7 (–9) racemes, 5–10 cm long borne along one side of a central axis (rachis) 4–12 cm long; rachis, broadly winged, foliaceous, triquetrous, 2–3.5 mm wide, ciliate on margins. Spikelets elliptic, cuspidate, 4–5 mm long, falling entire; glumes dissimilar, reaching apex of florets, thinner than fertile lemma; lower glume oblate, apex obtuse or acute, clasping; 0.33–0.5 length of spikelet, membranous, without keels, 11–13-veined; upper glume oblong, length of spikelet, membranous, without keels, 7-veined, surface pilose, hairy above, apex acute. 170,000–270,000 per kg.
U. ruziziensis: culms decumbent, stoloniferous forming a denser cover; racemes (3–) 5–7 (–9), 5–10 cm long; rachis 4–12 cm long, broadly winged, foliaceous, with rounded midrib, 2–3.5 mm wide; spikelets cuspidate, 4–5 mm long, packed in two rows along rachis; lower glume oblate, 11–13 -veined, apex obtuse; upper glume oblong, membranous, 7-veined, surface pilose, hairy above, apex acute.
U. brizantha: culms erect or geniculately ascending, more tufted habit; racemes (1–) 2–16, 4–20 cm long; rachis 3–20 cm long, crescentic in section, narrowly winged, 1 mm wide; spikelets subacute or acute, 4–6 mm long, packed in single row along rachis; lower glume ovate, 7–11-veined, apex obtuse or acute; upper glume oblong, cartilaginous, 7–9-veined, surface glabrous or pubescent, apex obtuse, or acute.
U. decumbens: culms decumbent, stoloniferous forming a denser cover; racemes 2–7, 1–5 cm long; rachis 1–8 cm long, flat, broadly winged, 1–1.7 mm wide; spikelets subacute or acute, 4–5 mm long, packed in 2 rows along rachis; lower glume ovate, 9-veined, apex obtuse or acute; upper glume oblong, membranous, 7-veined, surface pubescent, apex obtuse or acute.
Morphological differences are largely relative or numerically overlapping.
Africa: nyasi Congo (Swahili); itonto (Mosso region, Burundi); ndundwa (Ruzizi plains), lughutaghuta (Kinande, DRC)
Asia: rumput ruzi (Indonesia); ルジグラス ruji gurasu (Japan); หญ้ารูซี yaa roo see (ya roo si), หญ้าซูซี yaa susi (Central Thailand), หญ้าคองโก yaa congo (Thailand); cỏ ruzi (Vietnam)
European: herbe à Bengali, chiendent de la plaine de la rivière Ruzizi, chiendent du Zaïre (French); niederliegendes Palisadengras (German)
Latin America: braquiária-de-ruzizi, Braquiária-ruziziensis, capim Congo, capim-ruziziensis (Brazil); Congo señal, gambutera (also applied to other Urochloa spp.), Kenia, pasto Congo, pasto ruzi (Spanish)
Africa: Burundi, Democratic Republic of the Congo, Rwanda
Asia: Indonesia, Thailand, Vietnam
Caribbean: Puerto Rico
Central America: Guatemala
South America: Argentina, Brazil
U. ruziziensis can be grown on a range of soils providing they are well-drained and of moderate to high fertility. It is less tolerant of strongly acid conditions than U. brizantha and U. decumbens, and is best adapted to soils with pH between 5.0 and 7.0. There is some variation among genotypes in tolerance of high aluminum saturation on the exchange complex.
Average annual rainfall in the Ruzizi Plain for which U. ruziziensis was named is around 975 mm, over 4 seasons: the long dry season (June–August), the short wet season (September–November), the short dry season (December–January), and the long wet season (February–May). It has proven well-adapted to conditions in N Thailand where the annual rainfall average is 1,000 mm, with a wet season from May to October and a distinct dry season from Novermber to April. It has also grown well in parts of the humid tropics with annual rainfall of 3,000–3,500 mm. In general, it can perennate in areas with a dry season up to 4 months, and behave as a regenerating annual under extended dry conditions. It has poor tolerance of flooding, and does not persist on poorly-drained soils.
The altitude of its area of origin in the Lake Edward and Lake Kivu districts of Rwanda, Burundi and the Ruzizi plains in DRC ranges from 750 to 1,500 m asl at latitude about 3° S. Average annual temperature is about 24 ºC. While U. ruziziensis is best adapted to the warm lowland tropics, it has been grown successfully up to 2,000 m asl. Optimum growth occurs at 33/28 ºC day/night, and it exhibits little growth below a night temperature of 19 ºC. It is killed by heavy frost and regrowth is very slow after light frosts.
Ruzi has moderate shade tolerance and is grown under coconut plantations.
While U. ruziziensis exhibits a quantitative short day flowering response, there is considerable variation in flowering time among genotypes within the species, from late summer to mid-autumn in southern Brazil (Campo Grande, Mato Grosso do Sul, 20.5° S). Ruzi grass flowers in mid-autumn in northern Australia (South Johnstone, Queensland, 17.5° S) and October to November, with peak flowering near the end of October in N Thailand (Chiang Mai, 18.8° N). Unlike U. decumbens, an apomict, both diploid and tetraploid forms of U. ruziziensis reproduce sexually.
It can stand moderately heavy grazing and requires high levels of fertilizing to persist under frequent cutting.
Ruzi is sensitive to fire, and recovery after fire is slow.
Ruzi grass seed needs to be stored for at least 6 months after harvest to overcome dormancy, but quality deteriorates if seed is kept too long at high temperatures and high humidity. Seed can be treated with concentrated sulfuric acid for 15 minutes to break dormancy, but this poses dangers to the operator and to the seed if left too long in the acid or not washed thoroughly after treatment. Seed is normally sown at 2.5–10 kg/ha (depending on seed quality) onto a well-prepared seedbed and lightly covered, no deeper than 2 cm. Seedlings grow vigorously. Ruzi grass can also be established vegetatively using stem cuttings with rooting nodes.
Ruzi demands high soil fertility. Nutrient deficiencies, primarily P and K, should be corrected prior to planting, adequate maintenance fertilizer, particularly N, should be used to maintain productivity under grazing or cutting.
While ruzi grass forms a dense cover and competes with weeds under light grazing, the sward opens under heavier grazing, allowing broad-leaf weeds to establish. It will combine with a range of twining, erect and shrub legumes.
Grasses: not normally sown with other grasses.
Ruzi is severely attacked by spittlebug (Aeneolamia, Deois, Mahanarva, Zulia spp.; Hemiptera: Cercopidae) in tropical America. Nymphs and adults damage the host plant by sucking its sap and injecting a toxin, that initiates yellowing and death of the forage, making it unpalatable for cattle. Leaf is attacked by foliar blight (Rhizoctonia solani) in tropical America. Seed heads are attacked by an ergot fungus (Sphacelia/Claviceps) in DRC.
Ruzi spreads relatively slowly in existing vegetation by stolons and seed drop. Spread is more rapid where a clean seedbed is provided and soil fertility is sufficiently high.
Unlikely to become a weed of importance due to its relatively slow spread and high fertility requirements, but has potential to become a minor weed.
Good nutritive value, better than most other Urochloa spp.with CP commonly 7–13%, and up to 20%, and digestibility 55–75%. For ruzi grass hay cut 45 days after seeding in northeast Thailand, the IVDMD, crude fibre, NDF and ME concentrations were 61%, 80.5%, 72.8% and 7.9 MJ/kg, respectively.
Very palatable. Selective, heavy grazing pressure and the need for high soil fertility can result in the loss of ruzi grass.
Photosensitization may occur and some references suggest that ruzi grass should not be fed to sheep, goats or young cattle.
Less productive than U. decumbens in Australia and South America although yields have exceeded 20 t/ha/year with high rates of nitrogen. In Sri Lanka, DM yields of 16.8, 22.0 and 25.6 t/ha/year were achieved with N applications of 112, 224 and 366 kg/ha, respectively. On an oxisol at Coronel Pacheco, Brazil, ruzi grass produced 6.0 t/ha DM without added fertilizer and 12.0 t/ha with 150 kg/ha N fertilizer.
Liveweight gains have exceeded 1,000 kg/ha/year on pastures of ruzi with legumes, and over 1,500 kg/ha/yr with 200 kg/ha N fertilizer. Steers grazing B. ruziziensis on Brazilian savannas at 2 head/ha gained 285 kg/ha/year.
U. ruziziznesis has both diploid (2n = 2x = 18) and tetraploid (2n = 4x = 36) forms, both reproducing sexually with a high degree of cross-pollination within a ploidy level under conditions of natural open-pollination. Breeding programs have employed the ability of a tetraploid form of U. ruziziensis as the female parent to confer sexual reproduction ability to interspecific Urochloa hybrids involving the tetraploid , apomictic U. decumbens/U. brizantha complex (see fact sheet on Urochloa hybrids). The crossability between U. ruziziensis and U. decumbens is better than between U. ruziziensis and U. brizantha, and the hybrid seedlings obtained in crosses with U. brizantha are more frequently lethal.
Seed production is excellent. Ruzi exhibits a prolonged flowering period with uneven ripening of seed on individual inflorescences and quick shedding of seed when ripe, explaining why machine harvest yields are of the order of 125–200 kg/ha pure seed, and labour-intensive hand harvesting and ground sweeping yields are much higher, 400–600 (–1,000) kg/ha seed. In Thailand, hand-harvested seed heads are stacked about 1 m deep and allowed to sweat for about 3 days, the heads being turned daily to facilitate separation of seed from the head and to prevent overheating. Alternatively, the “living sheath” method is used, where heads are tied together in groups and effectively sweated in the field for 1–2 weeks before harvest. The grouped seed heads are shaken into a large net every 2–3 days until all seed is collected. Freshly harvested seed has a high percentage of dormancy(<20% germination). Primary dormancy is physiological, whilst long-term dormancy is mechanical, caused by a restriction of the seed coat. Dormancy may be broken by 6–9 months storage or by acid scarification.
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