Os resíduos oriundos do processamento da madeira constituem uma oportunidade para o aproveitamento energético, sendo a briquetagem um processo eficiente para concentrar a energia disponível da biomassa florestal. Nesse sentido, este trabalho teve por objetivo avaliar diferentes composições de resíduos das madeiras de mogno-africano (Khaya ivorensis e Khaya senegalensis) e eucalipto (Eucalyptus grandis x Eucalyptus urophylla) para produção de briquetes. Para isso, cinco composições foram testadas com diferentes proporções de resíduos (100% eucalipto, 75% eucalipto + 25% mogno-africano, 50% eucalipto + 50% mogno-africano, 25% eucalipto + 75% mogno-africano e 100% mogno-africano) e submetidas às análises químicas e físicas (extrativos totais, ligninas totais, teor de cinzas, teor de umidade, poder calorífico e densidade a granel). Os briquetes foram produzidos à temperatura de 120°C, pressão de 100 kgf cm-2 e tempos de compactação e resfriamento de 5 e 7 minutos, respectivamente, sendo submetidos a ensaios físico-mecânicos (densidade relativa aparente e resistência à compressão axial). As composições com maiores porcentagens de mogno-africano tiveram maior teor de extrativos e cinzas, e maior poder calorífico superior. Para os briquetes oriundos das composições com maiores porcentagens de eucalipto, verificou-se menor densidade relativa aparente e menor resistência à compressão axial. Apesar disso, os resíduos dessas espécies possuem potencial para a geração de energia, sendo os briquetes produzidos com maior porcentagem de mogno-africano, os que apresentaram maior potencial energético e resistência mecânica.

Decomposition processes and mineralization are essential to determine the time to deploy and manage species in consortia or rotations. The aim of this article was study the dynamics of biomass decomposition and release of macronutrients of plant residues of Fabacea. The species used were: jack bean (Canavalia ensiformis), pigeon pea (Cajanus cajan), dwarf mucuna (Mucuna deeringiana) and sunn hemp (Crotalaria juncea). The experiment was conducted in the field in a randomized block design, 4 x 5 factorial, four species of green manure and five times (0, 30, 60, 90, and 120 days). In the results, sunn hemp and pigeon pea had lower decomposition and release of C, N, K, and Mg. All species, K and P showed similar half-lives (t 1/2 ). For N, sunn hemp presented the lowest coefficient of mineralization (k), 0.0040 g g -1 dia -1 , associated with highest t 1/2 (173.3 days), already, jack bean showed the highest k (0.0122 g g -1 dia -1 ) associated with the lowest t 1/2 (56.8 days). In edaphoclimatic conditions, use of the jack bean and the dwarf mucuna is recommended for supply of nutrients in shorter periods of time for subsequent crops. However, sunn hemp and pigeon pea are recommended for greater persistence of mulch on the soil.

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The objective of this work was to evaluate the effects of increasing rates of biochar produced with coffee straw, at two pyrolysis temperatures, on the chemical attributes of an Oxisol cultivated with conilon coffee (Coffea canephora) and on the nutrient content of coffee tree leaves. Treatments consisted of pyrolysis at two temperatures (350 and 600 °C) and of five biochar rates (0, 5, 10, 15, and 20 Mg ha-1). The following soil chemical attributes were evaluated: pH in water; P, K, Ca, Mg, Al, H+Al, Zn, Cu, Fe, and Mn contents; effective and potential cation exchange capacity (CEC); sum of bases (SB); base (V) and aluminium (m) saturation; and N, P, K, Ca, Mg, Zn, Cu, Fe, and Mn contents in the leaves. The biochar produced at 600°C, at rates of 10 and 15 Mg ha-1, promoted a greater K release into the soil. Regardless of temperature, coffee straw biochar increased K and P availability, sum of bases, base saturation, and CEC in the soil, but did not influence macro- and micronutrient contents in the leaves. The addition of increasing rates of coffee straw biochar in the soil increases P, K, Mg, SB, CEC, and V, regardless of pyrolysis temperature.

Pastures cover, in Brazil, around 165 million ha, most of them are at some degradation level. Recovering these pastures is essential. The objective of this study was to evaluate the sensibility of soil organic matter (SOM) and its physical attributes in pasture soil at different degradation levels (1 to 4), Capoeiras (1 and 2) and secondary Forest (Control). Samples were collected at four depths (0.00-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.40 m). We verified higher values for SOM and hydraulic conductivity (Ko) in Forest, especially in the most superficial layer (0.00-0.05). We noted low values for macroporosity in this area. In all areas under Pastures lower values for Ko were observed in the superficial layer (0.00-0.05 m) when compared to layers 0.05-0.10 and 0.10-0.20 m, which indicates that the pasture management and cattle trampling negatively affect the physical quality of the pastures. For field capacity and wilting point the average values were observed in Pasture 4 (more degraded), which caused higher values for water availability. According to the principal components analysis, except for SOM at 0.20-0.40 m, all variables studied presented correlation above 0.6. From grouping analysis, we separated 3 groups: Forest; Capoeiras 1 and Capoeira 2 and Pastures 1 to 4.