Características nutricionais de plantas jovens de Bertholletia excelsa Bonpl. sob tratamentos de fertilizacąõ em área degradada na Amazônia

Among the alternatives for reintegration of deforested areas into the productive processes, one is the reforestation. However, the low natural fertility, the nutritional impoverishment of these areas by the removal of the forest cover and soil exposure, besides the lack of knowledge about the performance of tree species makes it difficult to define the best strategy of fertilization for the establishment of forest plantations in these areas. The aim of this study was to investigate the effects of mineral and organic fertilizations on the availability of nutrients in the soil, nutritional status and photosynthetic nutrient use efficiency in Bertholletia excelsa Bonpl. under forest plantations in degraded areas. The experimental design was completely randomized, with the variables: soil chemical composition, leaf nutrient contents, photosynthesis and photosynthetic nutrient use efficiency analyzed after four years from the planting. The effects of fertilization became especially noted in the superficial layers (0-2.5 and 2.5-7.5 cm) of soil. The mineral fertilization treatment increased the availability of K, Mg and Mn, while the organic fertilization raised the C and N soil contents. B. excelsa showed a higher leaf N (15.1 g kg-1), P (2.4 g kg-1), K (5.1 g kg-1), Zn (29.9 mg kg-1) and Mn (56.6 mg kg-1) under organic fertilization. The photosynthetic rates were three times higher in plants under organic fertilization compared to the control. The fertilization treatments improved the photosynthetic efficiency use of all nutrients, with emphasis on phosphorus use efficiency. Therefore, the higher leaf nitrogen content coupled with increased photosynthesis and phosphorus efficiency use in B. excelsa under organic fertilization represent important gains that may have contributed to the appropriate initial establishment of this species in the field