Quintais agroflorestais indígenas em área de savana (lavrado) na terra indígena araçá, Roraima

Abstract

Homegardens were studied in the Araçá Indian Land (5 communities), in Roraima s savannas (Lavrado), in order to analyze species composition, richness, diversity, dominance and factors that could influence the presence of tree and bush species in the homegardens, and verify changes in soil fertility in relation to the natural environment in savannas. A total of 79 species were found in the 60 homegardens studied, of which 45 species bear edible fruits. Sour Lime (Citrus aurantifolia Swing.), Araçá Trees (Psidium guineense SW.) and Mango trees (Mangifera indica L.) are the most numerous species at the homegardens, representing 13%, 13% and 11% of the total number of plants, respectively. They are also ones of the most common species, as they are present in 90%, 62% and 93% of the homegardens, respectively. Most fruits are used for self consumption; however the sour limes, mangoes and oranges arecommercialized in 40%, 15% and 8% of homegardens, respectively. The number of species and the total amount of plants are related to the size and age of the homegardens (p<0, 01). Planted species are generally collected through exchanges of seeds and seedlings among family members and friends, and each species may come from one or more places, mainly from the Araçá Indian Reservation (75%) and from Boa Vista (49%). From the total number of species present at the homegardens, 21 grown spontaneously, and are kept at the home gardens because they were useful somehow, mainly because they can bear edible fruits, in this case 46% of these species. From the 60 homegardens studied in the 5 communities, fifteen were chosen randomly in order to get soil samples, and were classified in 3 categories, according to age: new homegardens (0 to 10 years old); settled homegardens (15 to 35 years old) and old homegardens (40 years old or more). As homegardens were checked, a nearby savanna was sampled too, and it was considered to be evidence, in order to compare the levels of the elements at the homegarden soils and at the nearby savanna soils. Soil sample was done at three layers (0 to 10 cm, 10 to 20 cm and 20 to 30 cm). Most of the gardens and nearby areas are sandy. There was a significant relation among the garden age and calcium, potassium, magnesium, phosphorus, zinc and organic matter, showing that these nutrients levels increase along the years. Comparing savanna nearby areas, at new gardens it is already possible to notice higher element levels, at at least one community or soil layer, phosphorus being the main element increased at these homegardens. At settled and old homegardens there are even more cases where the difference between gardens and savanna is significant. Most part of soil at settled and old homegardens showed average levels of magnesium (levels varying between 0,2 and 0,8 cmolc kg-1) and high levels of zinc (more than 1,5mg kg-1) and phosphorus (variation: 3-7 mg kg-1). Iron showed little changes in levels when comparison was made between savannas and homegardens of all ages. Homegardens soil and nearby areas show low level of aluminum toxicity (less than 0,5 cmolc kg-1). In general homegardens showed low level of organic matter (less than 15g kg-1), probably because most soils are sandy. The analysis of cluster grouping showed that settled and old gardens were similar. They represent the group with the highest levels of nutrients. It conveys that period of time for settled gardens (about 15 and 35 years old) is enough to produce results that could be similar to the ones present in old gardens (more than 40 years old). The increased chemical characteristics at T.I. Araçá homegarden soils are due mainly to organic residues deposition and burning small quantities of vegetal residues, associated to species diversity and a closer andamoreaoptimizedanutrientacycling.