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RESUMOO aproveitamento de resíduos agroindustriais na forma de composto orgânico, pode resultar em maior sustentabilidade para sistemas agrícolas. Propôs-se, neste trabalho, analisar a qualidade final do composto orgânico em relação à composição em nutrientes e à presença de substâncias toxocologicamente ativas. Avaliaram-se as combinações de talo de fumo triturado, esterco e rúmen bovino (TF+EB+RB), talos de fumo, esterco bovino e Microsept-Pó (TF+EB+MP) e talos de fumo mais esterco bovino (TF+EB). Amostras médias de cada composto foram analisadas para determinação da concentração em macro e micronutrientes, aos 60 e 120 dias e, para verificar a concentração de nicotina e a presença ou não de resíduos agrotóxicos na matéria-prima (TF) nos compostos obtidos aos 120 dias. Os dados obtidos demonstraram alta concentração de potássio (K), nitrogênio (N), cloreto (Cl) e ferro (Fe) no composto final em relação aos demais macro e micronutrientes. Não se detectaram resíduos de agrotóxicos na matéria-prima (TF) nem a presença de nicotina nas amostras obtidas aos 120 dias, demonstrando ausência de risco de impacto ambiental no uso agrícola desses compostos. No final do processo de compostagem a mistura TF+EB foi a que resultou no composto orgânico com maior concentração em macro e micronutrientes.Palavras-chave: análise química, potencial nutricional, Nicotiana tabacum L Evaluation of the nutritional quality of organic compost produced with tobacco residues ABSTRACTThe use of agroindustrial waste to produce organic compost can result in greater sustainability for agricultural systems. This study aimed to analyze the final quality of the organic compost, according to their nutrients and the presence of active toxic substances. The combinations of ground tobacco stem, bovine manure and rumen (TF+EB+RB), tobacco stem, cattle manure and Microsept Dust (TF+EB+MP) and tobacco stem and cattle manure (TF+EB) were evaluated. Mean samples of each compost were analyzed to determine the concentration of micro and macro nutrients at 60 and 120 days and to verify the nicotine concentration and the presence or absence of pesticide residues in the raw material (TF) and in the composts obtained at 120 days. The data obtained showed high concentrations of potassium (K), nitrogen (N), chloride (Cl) and iron (Fe) in the final compost compared to the other micro and macro nutrients. Neither pesticides in the raw material (TF), nor presence of nicotine in the mean samples obtained within 120 days was detected, demonstrating the absence of environmental impact risks in the agricultural use of these composts. At the end of the composting process, the mixture TF+EB was the one which resulted in an organic compost with the highest concentration in micro and macro nutrients.

Grasses such as sugarcane (Saccharum spp.), maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) with C4 photosynthetic system are important crops that can host endophytic bacteria capable for biological nitrogen fixation (BNF). However, fixation measurements have yielded conflicting results. We determined BNF of five sugarcane and two sorghum varieties, maize and Guinea (Panicum maximum Jacq), elephant (Pennisetum purpureum Schum) and buffel (Cenchrus ciliaris L.) grasses in a pot experiment, using the 15 N natural abundance technique, with a soil naturally rich in 15 N (δ 15 N > 16 ‰) and two reference species (castor bean, Ricinus communis L., and cotton, Gossypium hirsutum L.) that absorb only N from the soil (average δ 15 N = 9.2 ‰). The initial results showed that no fixation occurred in elephant and buffel grasses. Sorghum, maize, Guinea grass and four sugarcane varieties had δ 15 N signals significantly lower than both reference species, indicating that they absorbed N from the atmosphere (δ 15 N = 0 ‰). The differences in signals from the reference species translates into proportions of plant N content originating from BNF varied from 12.8 to 19.4 % for sugarcane, 22.4% for maize, 20.9% for Guinea grass, and 24.7 to 31.2 % for sorghum. Nitrogen fixation by these species represents a potential of great fertilizer economy and high yields in low input agriculture.