Naturalized legumes in the Cauto Valley, Cuba
I. Gómez1, E. Cordoví1, D. G. Benítez1, R. C. López1, Y. Nuviola1 y Yuseika Olivera2
1Instituto de Investigaciones Agropecuarias "Jorge Dimitrov"
Carretera Bayamo-Manzanillo km 16½, Bayamo CP 85100, Granma, Cuba
2EEPF «Indio Hatuey». Matanzas, Cuba
With the objective of prospect and collect the naturalized legumes for livestock production usage in the Cauto Valley, Cuba, two searches were made in representative zones of the region. The first search was conducted in the territory located west of Bayamo city, where there are different soils and rainfall regimes, and the second one on soils affected by salinity. In prospection number 1 the presence of 17 genera was determined and within them a total of 22 species, among which the following prevailed: Galactia spiciformis, Centrosema molle, Desmodium triflorum and Teramnus uncinatum; the existence of an important number of species was also known on vertisol soils with deficient drainage, which edaphic grouping constitutes the most extended in the region, and on the other hand, the associability degree of each legume with other species of the spontaneous vegetation present in the search areas, was characterized. In prospection number 2 four and five genera were found on areas with weak and moderate fertility levels, respectively, and Desmanthus virgatus stood out due to the abundance in the number of individuals. It is concluded that under the conditions these prospections were made, there is a rich potential of naturalized legumes with multiplication and usage possibilities in the region.
Key words: Legumes, salinity, soil type
The protein deficit and the increase in the price of concentrate feedstuffs and nitrogen fertilizers in the world market are the main causes that motivate the use of legumes as an agroecological alternative to counteract the deficiencies in animal feeding in Cuba.
The American tropic is highly rich in native legumes adapted to different edaphoclimatic conditions, among which the herbaceous species belonging to the genera Centrosema, Desmodium, Stylosanthes, Calopogonium and Macroptilium, and the trees Leucaena, Gliricidia, Prosopis and Acacia stand out (Chacón, 1998). Their utilization has been defined in recent years as an extremely important choice to solve the problems existing in sustainable livestock production (Álvarez et al., 1999), which revitalizes the interest in the search for naturalized plant genetic resources that can contribute significant benefits to livestock production.
The objective of this work was prospect and collect naturalized legume species, in representative areas of livestock production in the Cauto Valley, Cuba, for their later evaluation and utilization in the region.
MATERIALS AND METHODS
The prospection was conducted in two zones which characteristics are representative of the Cauto Valley. The first search was made in a territory located west of Bayamo city, in the areas comprised within the largest livestock production firm of Granma province. For that purpose, ten exploration zones were chosen, taking into consideration the diverse soil types and the variations present in the historical rainfall regime (table 1).
In each zone ten sampling spots were selected, separated by 50 m from each other, in which the observations were made in zigzag form according to the methodology proposed by
Hernández and Hernández (1991), and in a 10-m radius around the spot the following observations were made: presence of legumes, number of times they were found, distribution percentage (presence of the species in each sampled firm), existence of effective nodules in their roots, as well as the vegetation species that were associated, combined or mixed with these plants; in addition, samples were collected of the stems, leaves and inflorescences for their identification.
The second search was conducted in an area of 20 km2, corresponding to the «Manuel Fajardo» Genetics and Rearing Firm in Jiguaní, on a Vertisol soil (Hernández et al., 1999) affected by weak (1 300-2 600) and moderate (2 600-3 800) salinity gradients, which were adopted as fundamental criteria to establish the tolerance level of the species to the limiting factor of productivity in the chosen soils.
The descriptors consisted in determining the number of individuals, cover degree, quantity, associability, development status, vitality and presence of nodules of each species found. In both cases, the identification of the species was made by specialists of the University of Camagüey, Cuba, through the collected and preserved plant samples. The observations were made through 100 x 100 m sampling networks, and the survey of the species was done every 10 m, according to the methodology proposed by Braunt-Blanket (1985).
RESULTS AND DISCUSSION
The high distribution of the species Galactia spiciformis, Centrosema molle, Teramnus uncinatus, Desmanthus virgatus, Neptunia plena, Centrosema plumieri, Rynchosia minima and Centrosema virginianum stood out, which were distributed in 70% or more of the explored zones (table 2), including in their higher percentage the pastureland areas, where their presence fulfils functions in the quality improvement of the diet consumed by the animals and they make contributions to soil fertility. These plants were found in diverse proportions in previously-made explorations (Menéndez and Machado, 1978; Olivera et al., 2008) in a much wider area of the eastern territory.
These results are important because the open character of some species is proven, showing wide adaptation capacity to the prevailing ecological conditions in the region. With the exception of Teprhosia cinerea, all the others were present on Vertisol and clayey soils with regular to deficient drainage, which represented more than 50 % of the soils dedicated to livestock production in this province, which coincides with the searches conducted by other authors under similar conditions in the central region of the country (Álvarez et al., 2001; Toral et al., 2006). This allows further work about the utilization under those conditions of natural species, considering as such those plants that originate from a certain country or were introduced several years ago, and are fully adapted to the environment (Funes, 2007).
The appearance of nodules in most of the accessions and sampling zones is also an important aspect to be considered, if the positive contributions made by legumes to the improvement and conservation of the environment are taken into consideration (Altieri, 2001; Fontes, 2007).
In spite of the large genetic diversity of the legumes found, a large number of them showed nodules at the sampling moment. This means that these accessions are infected by rhizobia; this process includes the infection of the root system, nodule formation and their senescence in certain phenological stages of the plant (Bécquer, 2002), which are incorporated to the soil and increase its quality. Teramnus labialis stands out as a promising natural legume for many regions of Cuba; in this sense, it is reported that it can nodulate naturally, although it shows specificity for certain Rhizobium strains (Tang et al., 1982; López et al., 2002).
Table 3 shows 11 plant communities which to some extent showed associative living with the legumes. Panicum maximum (86%), Bothriochloa pertusa (77%) and wide-leaf species (82%) were the plant groups which showed higher association degree. This associative character of legumes with prostrate or twining stems shows the possibility of higher exploitation of these plants in silvopastoral systems and of higher utilization of that condition within sustainable agroecological systems, due to the special importance of their usage in mixed pasturelands (Gómez et al., 2000). In other studies conducted in Cuba the expression of this characteristic was found in several of the prospections performed (Toral et al., 2006; Muñoz et al., 2007; Olivera et al., 2008), for which the need emerged to produce seeds and multiply, as soon as possible, the promising ecotypes within the ecosystem in which they prevail.
Some species found in this research show negative aspects. For example, Crotalaria retusa, Abrus precatorius, Macroptilium lathyroides and T. cinerea are known as toxic species for cattle (Harvard.Duclos, 1978); while Calopogonium coeruleum and N. plena are rejected by the animals due to their low or nil palatability. In spite of these undesirable characteristics from the point of view of animal feeding, such species could be used as living barriers against fires, green manures or cover for soil conservation.
The second exploration indicated the presence of five legumes on moderately saline soils, among which D. virgatus was promising due to the number of individuals found, although all the plants showed good vitality and tolerance to saline stress (table 4).
In weakly saline areas the same species were identified (with the exception of M. lathyroides) as in the moderate gradient; the best performance, in its natural form, was shown by D. virgatus (table 5).
The abundant presence of Desmanthus individuals on Vertisol soil has a close relationship to the results reported by Glatzle and Cabrera-Cardus (1997) on clayey soils of the Paraguayan Chaco. Although T. labialis was not present among the species found under these conditions, it is important to state that on saline soils of up to 5 000 ppm in Guantanamo population stability and high dry matter production (16,7 t/ha/year) have been reported, and they are found in association with sugarcane, basic crops and in marginal zones with high foliage volume (Guillot and Acuña, 2007). Other authors report that it is naturalized in Cuba on several soil types, even on saline (Oquendo et al., 2006) and hydromorphic ones (Machado and Roche, 2004; Machado et al., 2005). These results are highly interesting, because they allow undertaking amelioration and conservation actions of the agricultural soils affected by salts, which reach 53% in the country (Martínez, 1999); in Granma province 227 300 ha are reported which represent more than the fifth of the national total.
It is concluded that in the most representative ecosystems of livestock production in Granma province (including moderate and weakly saline soils) there is a wide availability of plant genetic resources within the legume family, which suggests the performance of selection, multiplication and seed production studies for their propagation and utilization in higher proportions under these conditions.