Cratylia argentea (Desv.) Kuntze
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Cratylia argentea (Desv.) Kuntze
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Leguminosae
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Authors:
Michael Peters and Rainer Schultze-Kraft |
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Common names Cratylia Cultivars Veraniega (mixture of accessions CIAT 18516 and 1868), Costa Rica (Argel et al., 2001) Description As a genus only recently receiving wider attention, basic studies such as on the taxonomy and reproductive behaviour of Cratylia argentea are limited, with bio-geographic circumscription being one of the most reliable classification approaches (Queiroz & Coradin, 1996). The genus Cratylia belongs to the subfamily Papilionoideae, tribe Phaseoleae and subtribe Diocleinae. The following description is adapted and expanded from Argel et al. (2001). Cratylia is a perennial, deep-rooting shrub reaching between 1.5 and 3 m in height; when associated with higher plants it can show a somewhat voluble habit. However, also trees of up to 6 m have been found as well as completely prostrate plants. Leaves are trifoliolate; leaflets are broadly-ovate with a silvery pubescence on their undersurface. Flowers are arranged in an elongated, many-noded pseudoraceme up to 30 cm long, with 6-9 flowers per node. Size of flowers ranges from 1.5-3 cm (length and width); petals are lilac or, very exceptionally, white. Pods are straight, flat, up to 20 cm long and 1-2 cm broad, dehiscent, containing 4-8 oval to almost circular seeds of about 1.5 cm diameter. Seeds are dark yellow to brown, when maturing under high-humidity conditions, dark brown. Thousand Seed Weight is about 220 g, i.e. there are about 4500 seeds per kg. Geographic distribution and adaptation Basic passport data of collected germplasm accessions can be accessed on the Internet (http://singer.cgiar.org/). C. argentea is found exclusively in South America. Its geographic distribution extends between 4° and 18° S from Northeast Brazil to Central and West Brazil and Bolivia and Peru east of the Andes (longitudinal range: 39-77° W). Collection sites concentrate on the subhumid Cerrados region of Brazil. In comparison with other Cratylia species, C. argentea is found in a wider range of habitats, with altitudes between 180 and 930 m asl, and main vegetation types ranging from Cerrados-Caatinga transition to Cerrados and seasonal forests; soils are mostly well drained, sandy loams (Queiroz & Coradin, 1996; Pizarro et al., 1997). During the last decade, C. argentea has been studied, mainly in tropical America, in environments ranging from wet to dry tropics, with 1000-4000 mm annual rainfall and up to 6 dry months; soil pH ranged from 3.8 to 5.9 (Argel & Lascano, 1998). Though apparently adapted also to higher pH soils, initial development of C. argentea in such soils is very slow. Reasons are not yet well understood. C. argentea is not well adapted to altitudes above 1200 m asl and needs well-drained soils (P. Argel, personal communication). It has been observed to survive bush fires. So far one cultivar, cv. Veraniega, has been released in Costa Rica, as the result of an initial collection in Brazil of 11 accessions in the early 1980s. More recent collections have broadened the genetic base of C. argentea and 40-50 accessions are currently under evaluation by CIAT in Colombia and Costa Rica. Morphological differences among accessions appear to be limited. Agronomic performance C. argentea is established best by seed, through plant nurseries or – more commonly– direct seeding; vegetative propagation trials with cuttings were not successful. Seed does not require scarification and is superficially sown at less than 2 cm depth. C. argentea nodulates readily with promiscuous cowpea rhizobia, though inoculation with Bradyrhizobium strains CIAT 2561 or 3564 is beneficial, in particular in acid soils with high aluminium saturation (Argel et al., 2001; Pizarro et al., 1996). C. argentea is established at planting distances of 1 m between rows and 0.5-1 m between plants within the row. Xavier et al. (1998) found under glasshouse conditions a positive response to calcium application of up to 1.5 t lime/ha in acid soils with high Al saturation. This contrasts with observations of slow establishment at higher pH levels under field conditions; hence further studies are needed for clarification. Generally, initial growth is slow but can be positively influenced by fertilization and inoculation with rhizobia (Argel et al., 2001). C. argentea can be cut for the first time four months after planting; it tolerates frequent cutting at intervals of 50-90 days even in the dry season, at a height of 30-90 cm above ground (Argel et al., 2000a; Argel et al., 2001). Plants cut at soil surface level have been observed to regrow extraordinarily well. Outstanding characteristics of C. argentea are its adaptation to acid soils and ability to retain leaves and to regrow during periods of extended drought. This drought resistance is associated with the deep rooting system of the species reaching up to 2 m in depth (Pizarro et al., 1996). Dry matter production is high, with 8-week regrowth yields of 2-5 t DM/ha , both in the dry and wet periods (Argel et al., 2001). On station, average yields of 50-150 g DM/plant for 8-week regrowth (CIAT, 2000; CIAT, 2001) and 110-330 g DM/plant for 12-week regrowth (Schultze-Kraft, 1996)are reported. Diseases and pests Up to now (2002) no major diseases and pests have been reported. In some sites, larvae of a beetle (Coleoptera: Melolonthidae) were observed to attack roots of C. argentea during establishment; this can lead to the death of individual plants (Argel & Lascano, 1998). Seed production Seed can be harvested from the establishment year onwards, though seed production in the first year is low. C. argentea seems to be insect-pollinated which can result in outcrossing (Queiroz et al., 1997); further studies are needed to define the level of outcrossing. Seed formation is affected by cutting time and height as well as phosphorus fertilization; positive results were found when C. argentea was cut back to 30 cm and fertilized with P at the beginning of the wet season. Seed production extends from the start of the dry season over 2-3 months; reported yields are 500-700 kg seed/ha and year (Argel et al., 2001). Seeds show neither a marked physical (hard seedcoat) nor physiological dormancy but storage under cool and dry conditions is necessary to avoid loss of viability when keeping seed for several months before planting (P. Argel, personal communication). Forage quality The nutritive value of C. argentea is among the highest reported for shrub legumes adapted to acid soils. Crude protein ranges between 18% and 30% of DM (Schultze-Kraft, 1996; CIAT, 2001), in vitro dry matter digestibility can reach 60-65%. (CIAT, 2001). In contrast to many other tropical shrub legumes, C. argentea only contains traces of tannins (Lascano, 1996; CIAT, 2001). It is readily consumed by cattle, though intake of immature Cratylia forage by sheep is low (Raaflaub & Lascano, 1995). Utilization On-station results with sheep have shown the value of C. argentea in supplementing a low protein diet and incrementing its voluntary intake, rumen digestibility, flow of nitrogen to the duodenum, total nitrogen and apparent nitrogen absorption (Wilson & Lascano, 1997). In trials with milking cows, supplementation of pasture with C. argentea and sugar cane resulted in an increase of 1.2-2.2 litres milk/cow/day in response to C. argentea increments in the supplement. Response to C. argentea was limited when cows of minor production potential were utilized or when the basal grass diet had CP levels above 7% (Argel & Lascano, 1998). Further information on the utilization of C. argentea has been gathered in on-farm trials mainly in Central America. C. argentea can be utilized both in mixed pastures with grasses and in fodder banks for in-situ grazing or for cut and carry for feeding as fresh forage or silage: Fresh forage as dry season supplement Due to its slow initial growth, biomass production of C. argentea in the first year after establishment is low. Based on production figures of 0.6-1 kg fresh material per plant in 60-90 days, the area needed for dry season supplementation can be calculated. Assuming 40% of C. argentea in the diet (complemented with 60% of sugarcane) 6-10 plants per day are necessary to feed a cow in the dry season (Argel & Lascano, 1998). In addition to its value as dry season supplement, C. argentea is used as a protein supplement to replace feed concentrates for dairy cows (Argel et al., 2001). Silage In Costa Rica, farmers have started to produce silage of C. argentea in order to conserve excess wet season feed for dry season supplementation (Argel et al., 2000b). Main attributes and shortcomings The main attributes of C. argentea are its drought tolerance due to a deep root system and its adaptation to acid soils. For shrub legumes adapted to acid soils, C. argentea is one of the few higher-quality species (Shelton, 2001). It is adapted to variable management and tolerates frequent cuttings, even in dry periods. It can be cut or grazed and fed fresh or as silage. Its main limitations are the lack of adaptation to altitudes above 1200 m asl and its slow initial establishment. Though seed production is good, care needs to be taken in storing seeds as these rapidly loose viability under suboptimal conditions. Links
References
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