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Influência de solos marginais na produtividade e no balanço energético da utilização de sorgo para energia
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A presente dissertação analisa a influência dos solos marginais na produtividade, na
qualidade da biomassa e no balanço energético do sorgo ( Sorghum bicolor L. ), avaliando o seu
potencial como cultura energética sustentável.
O estudo baseou-se na análise comparativa de artigos científicos dedicados à produtivi-
dade e à qualidade da biomassa e em cálculos energéticos realizados para diferentes rotas de
conversão: combustão, cogeração (CHP), gaseificação, pirólise, fermentação alcoólica e hidró-
lise/fermentação lignocelulósica.
A energia de entrada total no cultivo do sorgo foi estimada em 12,6 GJ/ha, incluindo
consumos de gasóleo, fertilizantes, sementes, pesticidas e maquinaria. Consideraram-se dois
cenários de produtividade: 4 t/ha, representando solos marginais com limitação hídrica ou
nutricional, e 45 t/ha, correspondendo a condições edafoclimáticas favoráveis.
Os resultados mostram que, em solos marginais (4 t/ha), as rotas termoquímicas mantêm
viabilidade energética, com NER entre 1,2 e 4,3, enquanto as rotas bioquímicas (fermentação e
hidrólise) apresentam NER < 1, refletindo balanços negativos. Já em condições ótimas (45 t/ha),
todas as rotas se tornam energeticamente favoráveis, com destaque para a combustão (NER ≈
41,2), cogeração (NER ≈ 24,1) e pirólise (NER ≈ 6,9).
A análise global confirma o baixo custo energético do sorgo face a outras culturas bioe-
nergéticas (como milho e miscanthus), aliado à sua elevada eficiência fotossintética, tolerância
ao stress hídrico e capacidade de cultivo em solos pobres.
Conclui-se que o sorgo constitui uma alternativa sólida e sustentável para a produção
de bioenergia, capaz de transformar áreas degradadas em sistemas produtivos, contribuindo
para a valorização de solos marginais, a redução das emissões de gases com efeito de estufa e
o avanço da transição energética.
This dissertation analyses the influence of marginal soils on the productivity, biomass quality, and energy balance of sorghum (Sorghum bicolor L.), assessing its potential as a sustai- nable energy crop. The study was based on a comparative analysis of scientific literature addressing sor- ghum productivity and biomass quality, as well as on energy balance calculations for different conversion routes: combustion, combined heat and power (CHP), gasification, pyrolysis, al- coholic fermentation, and lignocellulosic hydrolysis/fermentation. The total energy input for sorghum cultivation was estimated at 12.6 GJ/ha, including diesel, fertilizers, seeds, pesticides, and machinery. Two productivity scenarios were conside- red: 4 t/ha, representing marginal soils with water or nutrient limitations, and 45 t/ha, corres- ponding to favourable edaphoclimatic conditions. The results show that, under marginal soil conditions (4 t/ha), thermochemical routes remain energetically viable, with NER values between 1.2 and 4.3, while biochemical routes (fermentation and hydrolysis) present NER < 1, reflecting negative energy balances. Under optimal conditions (45 t/ha), all conversion routes become energetically favourable, with com- bustion (NER ≈ 41.2), CHP (NER ≈ 24.1), and pyrolysis (NER ≈ 6.9) standing out. The overall analysis confirms the low energy cost of sorghum compared to other bioe- nergy crops (such as maize and miscanthus), combined with its high photosynthetic efficiency, tolerance to water stress, and ability to grow in nutrient-poor soils. It is concluded that sorghum represents a solid and sustainable alternative for bioenergy production, capable of transforming degraded areas into productive systems, contributing to the valorisation of marginal soils, the reduction of greenhouse gas emissions, and the advan- cement of the energy transition.
This dissertation analyses the influence of marginal soils on the productivity, biomass quality, and energy balance of sorghum (Sorghum bicolor L.), assessing its potential as a sustai- nable energy crop. The study was based on a comparative analysis of scientific literature addressing sor- ghum productivity and biomass quality, as well as on energy balance calculations for different conversion routes: combustion, combined heat and power (CHP), gasification, pyrolysis, al- coholic fermentation, and lignocellulosic hydrolysis/fermentation. The total energy input for sorghum cultivation was estimated at 12.6 GJ/ha, including diesel, fertilizers, seeds, pesticides, and machinery. Two productivity scenarios were conside- red: 4 t/ha, representing marginal soils with water or nutrient limitations, and 45 t/ha, corres- ponding to favourable edaphoclimatic conditions. The results show that, under marginal soil conditions (4 t/ha), thermochemical routes remain energetically viable, with NER values between 1.2 and 4.3, while biochemical routes (fermentation and hydrolysis) present NER < 1, reflecting negative energy balances. Under optimal conditions (45 t/ha), all conversion routes become energetically favourable, with com- bustion (NER ≈ 41.2), CHP (NER ≈ 24.1), and pyrolysis (NER ≈ 6.9) standing out. The overall analysis confirms the low energy cost of sorghum compared to other bioe- nergy crops (such as maize and miscanthus), combined with its high photosynthetic efficiency, tolerance to water stress, and ability to grow in nutrient-poor soils. It is concluded that sorghum represents a solid and sustainable alternative for bioenergy production, capable of transforming degraded areas into productive systems, contributing to the valorisation of marginal soils, the reduction of greenhouse gas emissions, and the advan- cement of the energy transition.
Descrição
Palavras-chave
Sorgo Solos marginais Balanço energético Biomassa Bioenergia