Plantations d'eucalyptus et sidérurgie en Amazonie : apports du modèle 3-PG

Le secteur sidérurgique de Carajás, en Amazonie Brésilienne, fait l'objet de contestations environnementales du fait de sa forte consommation en charbon de bois. Ce charbon est essentiellement produit à partir de biomasse de forêts naturelles, avec des impacts directs et indirects sur la déforestation et la dégradation de ces écosystèmes. Les plantations d'eucalyptus à vocation énergétique installées sur des pâturages dégradés constituent une alternative intéressante. Peu de ces plantations ont été mises en place jusqu'à présent et faute d'évaluations valables de leur potentiel de production, une étude a été menée pour présenter une estimation consolidée de la croissance et de la productivité des plantations d'eucalyptus du pôle de Carajás. Celles-ci ont été obtenues à partir du modèle 3-PG (Physiological Principles in Predicting Growth). Son paramétrage a été réalisé à partir de données de croissance du massif d'eucalyptus d'une entreprise de la municipalité de Breu Branco dans l'État du Pará au Brésil. La calibration locale du modèle s'est avérée beaucoup plus performante que l'utilisation de paramètres établis pour des plantations d'eucalyptus dans d'autres régions du Brésil, d'Afrique du sud ou d'Australie. Les simulations réalisées indiquent que l'accroissement moyen annuel actuel de l'ordre de 20 m³ à l'hectare, obtenu pour une période de six ans, pourrait augmenter jusqu'à 30 m³ avec des fertilisations adaptées et un contrôle efficace du sous bois. Elles suggèrent aussi que des productions supérieures seraient obtenues sans déficit hydrique. Cela montre la nécessité de sélectionner les zones de plantation où la saison sèche est la moins marquée autour du pôle de Carajás. La calibration du modèle 3-PG a permis d'améliorer cet outil de gestion des plantations industrielles dans les conditions amazoniennes. (Résumé d'auteur

Charbon de bois et sidérurgie en Amazonie brésilienne : quelles pistes d'améliorations environnementales ? : l'exemple du pôle de Carajas

Le fonctionnement du secteur sidérurgique du pôle de Carajas, en Amazonie brésilienne, repose sur une importante consommation de charbon de bois. Étant donné les impacts directs et indirects de la production de charbon de bois sur la déforestation et la dégradation des forêts naturelles, cette filière de production fait l'objet de contestations environnementales croissantes. Cette publication analyse les alternatives d'améliorations environnementales de la filière charbon de bois destinée au secteur sidérurgique ainsi que les principaux freins techniques, économiques et institutionnels à leur adoption. Plusieurs alternatives sont envisageables, basées sur l'usage de technologies de carbonisation plus efficaces, le reboisement ou le boisement des terres dégradées et, dans une moindre mesure, l'utilisation de résidus d'exploitation forestière de faible impact. Certaines d'entre elles sont économiquement avantageuses sur le long terme et des financements peuvent être mobilisés pour faciliter leur adoption. Cependant, la régularisation de la situation foncière et environnementale apparaît comme un prérequis incontournable pour leur adoption. (Résumé d'auteur

Diversidade genética e caracterização fenotípica de Ochroma pyramidale em plantios no Mato Grosso, Brasil

This study evaluated balsa wood (Ochroma pyramidale) plantations in the search for matrices for genetic improvement. We were evaluated a total of 20 trees in plantations in Mato Grosso for genetic diversity with ISSR (Inter Simple Sequence Repeats) primers, as well as their diameter at breast height (DBH) and commercial height (CH). The primers amplified 111 loci (97.3% polymorphic), and the Nei genetic diversity (0.32) and Shannon index (0.48) indicate that there is genetic diversity in the plantations. The AMOVA revealed greater genetic variation within the plantations rather than among the plantations. The UPGMA group indicated the formation of nine groups, four of which had one individual each. As for phenotypic characterization, individuals 48 and 52 stand out for having higher DBH, and individuals 30 and 34 presented higher CH. Considering DBH and CH concomitantly, 12 individuals are within the standards. In the evaluated plantations, there is sufficient variability for the identification of balsa wood matrices.Este estudo avaliou plantações de pau-de-balsa (Ochroma pyramidale) em busca de matrizes para o melhoramento genético. Foi avaliado um total de 20 árvores em plantações no Mato Grosso quanto à diversidade genética com iniciadores ISSR (entre sequências simples repetidas), quanto ao seu diâmetro à altura do peito (DAP) e altura comercial (HC). Os primers amplificaram 111 locos (97,3% polimórficos), sendo que a diversidade genética de Nei (0,32) e o índice de Shannon (0,48) indicam que há diversidade genética nas plantações. A AMOVA revelou maior variação genética dentro das plantações do que entre as plantações. O agrupamento UPGMA indicou a formação de nove grupos, sendo quatro deles com um indivíduo cada. Quanto à caracterização fenotípica, os indivíduos 48 e 52 se destacam por apresentarem DAP mais elevado, e os indivíduos 30 e 34 apresentam HC superior. Considerando DAP e HC concomitantemente, 12 indivíduos estão dentro dos padrões. Nos plantios avaliados, há variabilidade suficiente para a identificação de matrizes de pau-de-balsa

Distribuição horizontal e vertical de fósforo em sistemas de cultivos exclusivos de soja e de integração lavoura‑pecuária‑floresta

The objective of this work was to evaluate the horizontal and vertical distribution of soil phosphorus and soybean yield in single‑crop and in integrated crop‑livestock‑forest (ICLF) systems. The evaluated treatments were: forest planted with eucalyptus; soybean crop and off-season corn intercropped with Urochloa brizantha 'Marandu'; U. brizantha pasture; ICLF system; and two control areas, with native forest and fallow. Soil samples were taken at the depths of 0–5, 5–10, 10–20, 20–30 cm for determining chemical characteristics. Evaluations were done in the second crop year after the implementation of the experiment. In the ICLF system, soil and yield were evaluated in four equidistant transects, at the center of the tree rows, and at 3, 6, 10, and 15 m from the rows on the northern and southern sides. Available P levels (Mehlich‑1) were greater at the upper soil layers, in the systems with soybean/off-season corn and ICLF. In ICLF, available P contents did not differ between the distances from the tree rows, and soybean yield did not differ from the one observed in the soybean/off-season corn system. Therefore, a two‑year ICLF is not yet capable of major interference on soil chemical characteristics and on soybean yield.O objetivo deste trabalho foi avaliar a distribuição horizontal e vertical do fósforo no solo e a produtividade de soja em sistemas de cultivos exclusivos e de integração lavoura‑pecuária‑floresta (ILPF). Foram avaliados os tratamentos: floresta plantada de eucalipto; lavoura de soja e milho safrinha consorciado com Urochloa brizantha 'Marandu'; pastagem de U. brizantha; sistema de ILPF; e duas áreas controle, com floresta nativa e pousio. O solo foi coletado nas camadas de 0–5, 5–10, 10–20 e 20–30 cm, para determinação das características químicas. As avaliações foram realizadas no segundo ano agrícola após a implantação do experimento. No sistema de ILPF, solo e produtividade foram avaliados em quatro transectos equidistantes, no centro do renque e a 3, 6, 10 e 15 m do renque, nas faces norte e sul. Os teores de P disponível (Mehlich‑1) foram maiores nas camadas superficiais do solo, nos sistemas com soja/milho safrinha e com ILPF. No ILPF, os teores de P disponível não diferiram entre as distâncias do renque das árvores, e a produtividade de soja não diferiu da observada no sistema com soja/milho safrinha. Portanto, com dois anos de implantação, o sistema ILPF ainda não é capaz de interferir marcadamente nas características químicas do solo e na produtividade da soja

Organogênese in vitro de limão cravo

Rangpur lime (Citrus limonia Osbeck) in vitro organogenesis was studied based on explant type and cytokinin culture media supplementation. Four explants types collected from epicotyl or hypocotyl regions of in vitro germinated seedlings were evaluated. The epicotyl-derived explants consisted of epicotyl segments and the hypocotyl-derived explants consisted of the entire hypocotyl segment, the hypocotyl segment attached to a cotyledon fragment, and the hypocotyl segment divided longitudinally. The explants were cultured on EME culture medium supplemented with benzylaminopurine (0, 0.5, 1.0, or 1.5 mg L-1). The evaluation was performed after 6 weeks. Best results considering both the explant responsiveness and number of shoots developed per explants were obtained when epicotyl segments-derived explants were evaluated. Considering the explant responsiveness of hypocotyl segments-derived explants no difference was detected between the entire hypocotyl segment and the hypocotyl segment attached to a cotyledon fragment. Moreover, the percentage of responsive explants decreased when hypocotyl segments divided longitudinally were tested. No difference was detected for the number of shoots developed per explant considering the three types of hypocotyl-derived explants. Culture media supplementation with BAP was not essential for Rangpur lime in vitro organogenesis. However, adventitious shoot development was stimulated in concentrations between 0.5 - 1.0 mg L-1

Physical characteristics of soybean cultivated under the conditions of integrated agrosystems

Integrated crop-livestock-forest (ICLF) systems involve intercropping of various crops to achieve beneficial and synergistic outcomes, enhancing both economic viability and environmental sustainability. Considering the complexity of integrated agrosystems and the economic importance of soybean production in Brazil, we aimed to investigate the effects of two ICLF systems on the physical characteristics and quality of soybeans produced. The treatments comprised plots (two ha) with either single-row (ICLFS) or triple-row (ICLFT), tree configurations intercropped with soybean (maize and forage grass), and control plots (one ha), whose crops were cultivated under full sunlight (CFS). Soybeans were harvested from plants located at 3, 6, 10 and 15 m from tree bands in the north and south faces of the ICLF systems and at random positions in the CFS plots. The moisture content, electrical conductivity of the exudate solution, hue angle and chroma index of grains harvested from ICLFS and ICLFT were similar to those of CFS-grown soybeans. However, the mass of 1000 grains and the bulk density values of ICLF-grown soybeans were significantly higher (P ≤ 0.05) than those of grains harvested from CFS plots. We conclude that the quality of soybean seeds was not negatively affected by the conditions prevailing in the ICLF systems. Moreover, it appears that the forest component contributed positively to the ecosystem by providing a favorable microclimate for the development of soybean grains

Eucalyptus and Acacia mangium tree growth and stand production in pure and mixed-species plantations along an ecological gradient in Brazil

The association of Acacia could increase Eucalyptus plantations productivity through a positive balance between facilitative effects and competition between species. In Brazil, the development of mono-specific stands of Acacia mangium (100A) and Eucalyptus sp. (100E) was compared with nitrogen (N) fertilisation treatment (100E + N) and mixed-species plantations in a 1:1 ratio (50A:50E). The study was conducted in Itatinga-SP, Sinop-MT and Colinas-TO with mean annual temperature of 19.4, 25.0 and 27.5 °C, mean annual rainfall of 1320, 2640, and 1850 mm, and dry season duration of 3, 5 and 7 months, respectively. The soils are sandy to sandy-clay. At 36 months, Eucalyptus height in 100E was 18.9, 10.9 and 13.7 m, in SP, MT and TO, respectively. For Acacia the corresponding values in 100A were 14.2, 13.5 and 10.8 m, respectively. This pattern, also observed for diameter at breast height, showed that Eucalyptus was proportionally more adapted to the ecological conditions than Acacia in SP, the opposite being found in MT. Stand basal area (SBA) was 2, 10 and 3 % higher in 100E+N than in 100E in SP, MT and TO, respectively. SBA was 7 and 1 % higher in 100E (8.33 and 3.70 m2 ha-1) than in 100A (7.77 and 3.66 m2 ha-1) in SP and TO, respectively. By contrast, SBA was 69 % higher in 100A (7.54 m2 ha-1) than in 100E (4.47 m2 ha-1) in MT. SBA was 6 and 4 % higher in 100E than in 50A:50E in SP and TO, respectively. By contrast, SBA was 21 % higher in 50A:50E than in 100E in SP. The occurrence of higher stand production in mixed species plantations of Eucalyptus and A. mangium than Eucalyptus monocultures depends on ecological conditions. When conditions permit high eucalypt stand yield as observed in SP, the potential N facilitation by Acacia cannot balance the lower potential of growth of Acacia trees, which are also deeply competed by Eucalyptus trees. By contrast, as observed in MT mixed plantations are likely more productive than Eucalyptus monoculture when the environmental conditions (hot and humid climate) are more favourable for acacia than eucalyptus and when the soils are deficient in N. Adverse conditions for both Eucalyptus and Acacia (e.g. extreme high temperatures, marked dry season) as found in TO are likely to prevent any efficient facilitation processes between species