Large‐scale bioenergy demand has triggered new approaches to straw management in Brazilian sugarcane fields. With the progressive shift from a burned to a nonburned harvest system, most of the straw presently retained on the soil surface has become economically viable feedstock for bioenergy production. The trade‐offs between the need to preserve soil quality and produce more bioenergy have been the subject of intense discussion. This study presents a synthesis of available information on the magnitude of the main impacts of straw removal from sugarcane fields for bioenergy production and therefore represents an easily available resource to guide management decisions on the recommended amount of straw to be maintained on the field to take advantage of the agronomic, environmental, and industrial benefits. Crop residues remaining on sugarcane fields provide numerous ecosystem services including nutrient recycling, soil biodiversity, water storage, carbon accumulation, control of soil erosion, and weed infestation. Furthermore, several studies reported higher sugarcane production under straw retention on the field, while few suggest that straw may jeopardize biomass production in cold regions and under some specific soil conditions. Pest control is among the parameters favored by straw removal, while N2O emissions are increased only if straw is associated with the application of N fertilizer and vinasse. An appropriate recommendation, which is clearly site specific, should be based on a minimum mass of straw on the field to provide those benefits. Overall, this review indicates that most of the agronomic and environmental benefits are achieved when at least 7 Mg ha−1 of dry straw is maintained on the soil surface. However, modeling efforts are of paramount importance to assess the magnitude and rates of straw removal considering the several indicators involved in this complex equation, so that an accurate straw recovery rate could be provided to producers and industry toward greater sustainability.

Brazil is a major sugarcane producer and its production more than doubled over the last decades to meet global bioenergy demands for reducing crude oil dependency and mitigating climate change. Nevertheless, the adverse effects of this growth on jeopardizing the sustainability of sugarcane production are not known, especially when environmental impacts of agricultural inputs and production processes are not judiciously managed. This article is a comprehensive review of the state-of-the-knowledge and the main advances made thus far in the sugarcane sector. Here, we review the major environmental impacts of rapidly expanding sugarcane plantation on the land use change and its competition with food production, as well as those associated with sugarcane cultivation in Brazil. Our main finding are that sugarcane plantation did not contribute to direct deforestation, and its expansion on degraded pastures with the attendant increased yields of food crops and livestock intensification decreased land competition between food and sugarcane. Non-burning sugarcane harvesting is a win-win strategy because of its benefits involving agronomic and environmental aspects, but soil compaction is among the main issues in sugarcane cropping systems. Sugarcane is highly efficient in terms of nitrogen use efficiency, which is an important factor for its high energy balance. But, special attention should be given regarding emissions of nitrous oxide when straw mulching is combined with application of nitrogen fertilizer and vinasse. Recent advances in the sugarcane sector also show significant reductions in water consumption, making sugarcane ethanol one of the most favorable options in terms of water footprint. Growing realization of a vast potential indicates the need to further enhance the environmental benefits of sugarcane ethanol by optimizing the agricultural production chain. Based on this improved knowledge, the adoption of best management practices is among researchable priorities that can be developed to consolidate the large potential of sugarcane production towards greater sustainability.

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RESUMO O solo é um importante compartimento de C e exerce papel fundamental sobre a emissão de gases do efeito estufa e consequentes mudanças climáticas globais. Mudanças no uso e manejo do solo podem causar tanto efeito negativo como positivo no que se refere à emissão de gases de efeito estufa para a atmosfera. Entretanto, atualmente tem sido constatada a intensificação do aquecimento global, causado pelo aumento das emissões dos gases responsáveis pelo efeito estufa, oriundos principalmente da queima de combustíveis fósseis, do desmatamento e do uso inadequado do solo para agricultura. O uso e manejo inadequado do solo, além de contribuir para o efeito estufa, ainda traz problemas relacionados à sua sustentabilidade devido à degradação da matéria orgânica do solo, o que atinge negativamente os seus atributos físicos e químicos, bem como sua biodiversidade. Por outro lado, práticas adequadas de manejo, que visam à manutenção ou mesmo o acúmulo de C no sistema solo-planta, podem atenuar os efeitos do aquecimento global. Essas práticas de manejo podem ser: implementação de sistemas de plantio direto, recuperação de pastagens degradadas, implantação de sistemas integrados de cultivo, reflorestamento de áreas marginais, uso de espécies que tenham alta produção de biomassa, eliminação de queimadas, entre outras. O objetivo desta revisão foi avaliar algumas das principais fontes de gases do efeito estufa relacionadas à agricultura e mudança do uso da terra e, ainda, apresentar estratégias para mitigar tais emissões e aumentar o sequestro de C no sistema soloplanta, em três dos principais biomas do Brasil.Termos de indexação: uso da terra, emissão de gases do efeito estufa, estoque de carbono no solo, aquecimento global.(1) Recebido para publicação em maio de 2008 e aprovado em dezembro de 2009.