MINERAL COMPOSITION OF ARBOREAL AND BUSH SPECIES OCCURRING IN PASTURES, IN PERNAMBUCO-BRAZIL

The aim of the present study was to evaluate, during the dry and wet seasons the mineral composition of tree and bush species occurring in pasture areas near the cities of Itambé, Caruaru and Serra Talhada in the humid, intermediate, and dry climatic zones of the state of Pernambuco (Brazil). Leaves and branches up to 5.0 mm in diameter were collected for the determination of N, P, Mg and K concentrations. Five, 8, and 14 tree and bush species occurred in the pastures of Itambé, Caruaru and Serra Talhada respectively. In Itambé, N content was influenced by species, while P and K contents were affected by species and season. In Caruaru, N, P and K contents were not influenced by season and in Serra Talhada, only P and K contents were influenced by species and season. Chemical composition was generally more adequate in the rainy season.


INTRODUCTION
Pasture livestock farming systems consist of a natural combination or a deliberate association of one or more ligneous (bush and arboreal) components within a pasture of native or cultivated grass and herbaceous leguminous species and their use with ruminants and herbivores (Ribaski and Montoya, 2001).The chemical composition of species with a ligneous component must be assessed in order to indicate such species as alternatives for pasture livestock farming systems, especially during the dry season, when there is less availability of the herbaceous components in the pasture (Reis et al., 2006).According to Souza et al. (2006), scarce natural resources in semi-arid regions of Brazil, along with periodic droughts and the high demography of the region, force the northeastern region of the country to periodically turn to native and exotic plants that are able to contribute towards subsistence of livestock farming.
According to Carvalho et al. (2001) and Febles et al. (2001), the following are the main characteristics that indicate an arboreal/ bush species as potential fodder for composing a pasture livestock farming system: high germination; ease in establishment; high capacity for re-budding; capability to provide nitrogen and other nutrients to the pasture; adaptation to the environment; tolerance to drought, frost or inundation of the soil; capability to provide palatable fodder; tolerance to pests and diseases; absence of toxic effects on animals; capability to provide shade and shelter; high fodder yield potential; deep roots; efficiency in the use of light; and compatibility with the herbaceous components of the system.
The qualitative assessment of the nutrients in the vegetal component of an agro-forestry system is fundamental to the selection of species with fodder potential that are able to provide a balanced diet rich in protein, energy and minerals.Qualitative assessments also help identify vegetal matter that is toxic to plant hat are toxic for the animals (Franke et al., 2001).Imbalance in an animal diet, particularly minerals, may result in serious nutritional disorders, with a negative impact on the productive and reproductive performance of the animals (Leonel et al., 2006).
The aim of the present study was to assess the mineral composition of arboreal and bush shrubby species occurring in pastures located in Itambé, Caruaru and Serra Talhada in order to obtain information that may contribute toward the diagnosis and planning of pasture livestock farming systems in the state of Pernambuco (Brazil).

MATERIALS AND METHODS
The study was carried out in pasture native and cultivated areas of the experimental fields of the Pernambuco Livestock Research Institute (IPA, Instituto Agrônomico de Pernambuco) in the counties of Itambé, Caruaru and Serra Talhada in the state of Pernambuco (northeastern Brazil).
Itambé is located in the humid, coastal zone, 96 km fromRecife (state capital).The climate is warm, rainy and humid, with a dry summer, a mean annual temperature of 24ºC and mean annual rainfall of 1200 mm.The vegetation is classified as deciduous and sub-deciduous forest (IPA, 1994).The soil is typified as Red-Yellow Argisoil, Red-Yellow Latosoil and Vertsoil (Embrapa, 1999).
Caruaru is located in the intermediate climatic zone in the interior of the state, 135 km from Recife.The climate is semi-arid, with a mean annual temperature ranging from 16.7° to 33.5°C and mean annual precipitation rainfall of 600 mm.The predominant vegetation is Hypoxerophile caatinga (IPA, 1994).The soil is typified as Red-Yellow Latosoil, Red-Yellow Argisoil and Neosoil (Embrapa, 1999).
Serra Talhada is located in the semi-arid region of the deep interior of the state, 418 km from Recife.The climate is semi-arid, very warm, with a mean annual temperature of 25.9°C and mean annual precipitation rainfall of 887.9 mm.The predominant vegetation is Hypoxerophile Caatinga (IPA, 1994).The soil is typified as Red-Yellow Argisoil, Red-Yellow Latosoil, Luvisoil and Neosoil (Embrapa, 1999).
Samples for chemical analysis were collected during the dry and humid seasons.Leaves and branches up to 5.0 mm in diameter were collected, dried and ground together for the determination of N, P, Mg and K. Analyses were carried out at the vegetal chemistry Laboratory of the Universidade Federal Rural de Pernambuco (UFRPE) following the methodology described by Bezerra Neto and Barreto (2004).Simultaneously, botanical material was collected for the identification of the arboreal and bush shrubby species in the pasture areas.Specimens were stored at the Sergio Tavares Herbarium of the Forets Science Department (UFRPE).The Cronquist classification system (1981) was used for the separation of the species into families., 2000).

RESULTS AND DISCUSSION
Table I displays a list of the species collected for chemical evaluation; among the study areas, the city of Serra Talhada had the greatest number of species ( 14), followed by Caruaru, (8) and Itambé (only 5 species recorded).Among the species Means followed by the different small letter in the same species differ according to F test (p<0.05);Means followed by the different capital letter in the same period differ according to Scott-Knott test (p<0.05).
collected, there was a predominance of native species and legume families.Carvalho et al. (2001), Gonçalves and Lelis (2001) and Queiroz et al. (2002) discuss the multiple uses of the different species evaluated in the 4 locations.Besides their importance as fodder, there are other uses that these species may have (table I).
Among the species collected in the Itambé region, leucena (white leadtree) had the greatest (table II) and bordão-de-velho had the lowest N content, regardless of season.The sampling period influenced the N concentration in the species sabiá, which was higher in the dry season.The N content for sabiá is similar to that described by Vieira et al. (2005) and Moura et al. (2006) in the same area.The N concentration in leucena is similar to that described by Oliveira (2000) in Petrolina (PE, Brazil).For espinheiro (Machaerium aculeatum), which was also found in the Itambé pastures, Ferreira et al. (2007) and Silva et al. (2007) respectively estimated 2.15 and 2.45% N for the average of the seasons (dry and rainy), which are similar to the reported in the present study.
A significant interaction (p<0.05)occurred between species and seasons, with regard to P concentration in Itambé (table II).The mean average P concentration in the species was higher in the rainy Means followed by the different small letter in the same species differ according to F test (p<0.05);Means followed by the different capital letter in the same period differ according to Scott-Knott test (p<0.05).
season and leucena (white leadtree) had the highest P content in this season.A significant interaction (p<0.05) was found for K content with higher values in the dry season (table II).Caubin had the highest K content in the dry season, whereas espinho-de-judeu had the highest K content in the rainy season.Mg variations were non-significant (table II).
N and P concentrations did not differ significantly (p>0.05) between species or seasons in Caruaru (table III).The species algaroba (mesquite), cana-fístula, catingueira, jurema-branca and jurema-preta had higher Mg values (p<0.05)than the chumbinho (table III) and they were not influenced by season.Average K content was higher in the dry season (p<0.05).
Regarding the data obtained in Serra Talhada, the species angico-de-caroço, joazeiro, moleque-duro and quixabeira had a higher N content concentration than other species (p<0.05) in the dry season, whereas only angico-de-caroço and catingueira do it in the rainy season (table III), thereby showing an interaction between species and season.The P and K concentrations were higher (p<0.05) in the dry season (table III) and K content concentration was higher in the rainy season.
The mineral content in plants is influenced by characteristics that are inherent to the species and environment.According to Larcher (2000), the proportion of various bioelements may be strongly determined by plant species and family, by organ or by stage of development.In general, N, P and K content varied in accordance with the species, season and locations, which may be associated to the high mobility of these minerals (Malavolta et al., 1989) as well as the immobility of magnesium in the plant (Epstein, 1974).
Phosphorus is one of the most important elements for cattle, especially cattle kept in pastures.Extensive areas of pastures with phosphorus deficiency occur throughout the world and there is no doubt that this is the most common mineral deficiency among cattle (Tokarnia et al., 2000).According to Moraes (2001), 0.12% P in the dry matter of tropical fodder is closer to the needs of cattle than levels established by the American National Research Council (overestimated at 30% for the conditions of the country).Thus, the content in most of the species evaluated in the three locations achieved this value.
Knowledge on the mineral composition of fodder in different locations and seasons provides information for the assessment of mineral and nutritional supplements for animal feeding.Furthermore, information on the degree of mineral extraction from different plants is important to the assessment of fertilizer possibilities.The species bordãode-velho collected in Itambé, marmeleiro and chumbinho collected in Caruaru and aroeira, baraúna, catingueira, imburana, jurema preta, mameleiro, moleque-duro, mororó, pau-de-leite, pereiro, quixabeira and umbuzeiro collected in Serra Talhada (tabla IV) exhibited N content concentration below 1.92%, which Araújo et al. (2001) consider the minimum satisfactory value of crude protein N. It should be stressed that, besides the chemical components of the species occurring in pastures, aspects such as ease of propagation, adaptation to climatic conditions, type of animal and objectives of the animal production system should be considered in the choice of species for use in pasture animal husbandry systems.
Regardless of the locations, the species analyzed exhibited different content concentration of N, P, Mg and K as a result of variations seasonal.It is noteworthy that the legume species may have an influence on N concentration.Chemical compositions was generally more satisfactory in the rainy season.

Table I .
Common and scientific names, family and main uses of evaluated species, according locations locale.(Nome vulgar, científico, família e uso das espécies avaliadas, conforme o local).

Table II .
N, P, Mg abd K contents mean ± SD by species, according to season of the year, Itambé-PE.(Teores media ± DP de N, P, Mg e K por espécie, conforme a época, Itambé-PE).

Table III .
N, P, Mg and K contents mean ± SD by species, according to season of the year, Caruaru-PE.(Teores media ± DP N, P, Mg e K por espécie, conforme a época, Caruaru-PE).

Table IV .
N, P, Mg and K contents mean ± SD by species, according to season of the year, Serra Talhada-PE.(Teores media ± DP de N, P, Mg e K por espécie, conforme a época, Serra Talhada-PE).