Biomass dynamics of fallow vegetation enriched with leguminous trees in the Eastern Amazon of Brazil.

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Resumo: The agricultural system used in sequence with fallow vegetation was maize and cassava. In the experimental timetable, maize grew essentially as monocrop, subject only to interactions with the slashed and burned re-growth. The maize yield was 1890 kg ha1, larger than what is generally obtained in the area studied. Cassava divided site resources with planted trees for enrichment during eight months until its harvest at the age of one year. The different trees planted for enrichment, regardless of spacing, did not have a negative impact on the dry weight of cassava root. The values of dry weight of cassava root varied as per the following: S. paniculatum (7120 kg ha-1)> A. angustissima (6750 kg ha-1)> l. edulis (6560 kg ha-1)> A. mangium (6320 kg ha-1)> C. racemosa (6100 kg ha-1) > control (6060 kg ha-1). The spacing of trees planted regardless of species, showed a significant reduction of cassava dry root-weight at the spacing of 1 m x 1 m (10000 tress ha-1) only, when compared to tree spacing of 2 m x 2 m. There appeared some advantage in having a light enrichment as seen from the following sequence: 2 m x 2 m (7140 kg ha-1) > 2 m x 1 m (6660 kg ha-1) > control (6060 kg ha-1) > 1 m x 1 m (5610 kg ha-1). These results show the possibility to maintain crop productivity in enriched fallow vegetation systems by planting leguminous trees. However, when food crops are the main goal, tree planting at the spacing of 1 m x 1 m should be carefully considered. During the development of enriched fallow systems planted trees and cassava grew together for as long as eigth months and later on, after crop harvest, trees developed with the natural vegetation. In this chronosequence the values of tree survival at 24 monhts of age were as follows: C. racemosa (99%), A. angustissima (98%). I. edulis (97%), A. mangium (91%) and S. paniculatum (90%). At 24 months of age, trees planted to enrich fallow vegetation showed different behaviors relating to height- and Dbh growth. Acacia mangium presented the best performace (7.1 m height and 5.6 cm Dbh) follwed by I. edulis (4.7 m and 3.5 cm), A. angustissima (4.5 m and 3.2 cm) and C. racemosa (3.4 m and 3.0 cm). Increased plant spacing did not influence growth in height, but caused significant reductions in growth in Dbh. The lowest diameters were observed at the spacing of 1 m x 1 m (3.2 cm) followed by 2 m x 1 m (3.9 cm) and 2 m x 2 m (4.3 cm). The annual dynamics of tree growth, evaluated by average height increment-MHI during the study period, were similar for all species. These growth dynamics demonstrate the existence of four phases of tree development. The first phase was characterized as seedling "adaptation" and occurend during the first six months after planting. MHI values are small, and this phase coincided with a period of low precipitation. The second phase, called "growth explosion", began with the start of the firts rainy season, between the sixth and eighth month of growth, when the highest MHI values were observed for all species planted. "Competition" characterized the third phase and occured from the eighth to tenth month. MHI values decrease due to fallow vegetation development, showing competition for site growth resource to exist. The last phase, denominated "stability" characterizes the maturation of the enriched fallow vegetation system. This phase, occurend between the 10th and the 24th month, and MHI values of trees planted slowly to decrease.

Ano de publicação: 1999

Tipo de publicação: Teses


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