The solid product of pyrolysis, called "biochar" (BC) in the context of improving soil properties as part of agronomic or environmental management, also got into focus as a climate mitigation strategy. The researcher investigated the effects of BC on soil attributes, nitrogen (N) use and GHG emissions. In Chapter 1 the origin of BC was commented. In Chapter 2, BC from sugarcane straw was characterized, and its priming on native SC was evaluated with the treatments: (T1) Soil; (T2) BC; (T3) Soil + BC 10 Mg ha^-1; (T4) Soil + BC 20 Mg ha^-1; and (T5) Soil + BC 50 Mg ha^-1. In Chapter 3, it was evaluated the combination of BC, filter cake (F) and vinasse (V), in relation to soil attributes and carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions. The treatments were: (T1) Soil + FC + V; (T2) Soil + FC + V + BC 10 Mg ha^-1; (T3) Soil + FC + V + BC 20 Mg ha^-1; and (T4) Soil + FC + V + BC 50 Mg ha^-1. In Chapter 4, the nitrogen (N) use efficiency was investigated in a pot trial under wheat using NH₄[¹⁵N]O₃ and rates of BC, with the treatments: (T1) Soil, with N, no BC; (T2) Soil, with N, BC 10 Mg ha^-1; (T3) Soil, with N, BC 20 Mg ha^-1; and (T4) Soil, with N, BC 50 Mg ha^-1. BC had C and N contents higher compared to the feedstock. Total K, Mg and P also increased. The lowest CO₂ fluxes were for BC, and CO₂ from soil and soil + BC did not differ. The highest CO₂ - C4 was in the first day, and there were no differences in the CO₂ - C3. The BC presents characteristics to improve soil attributes. BC stability is an opportunity to reduce CO₂ emissions. In Chapter 3, soil pH, P and base contents increased and Al³⁺ decreased with BC to sandy soil. Impacts of BC on the CEC were higher in sandy soil. Mineral N decreased with BC. Cumulative CO₂ in T1 were higher in sandy and clayey soils than the control. T2 and T3 in sandy soil increased CO₂ emissions, but T4 did not differ from T1. BC reduced N₂O emissions from sandy and clayey soils relative to T1. BC with FC and V affected pH, CEC, P and base contents. However, those effects were higher in sandy soil. The BC supressed N₂O from V and FC. In Chapter 4, BC decreased N₂O from N fertilization compared to only N fertilizer. T4 had higher tillering and grain yield. Also, T2 to T4 had higher 100-grain weight and shoot. T3 and T4 had the highest N in grains. The application of BC to soil improves N availability and use efficiency, enhances grain yields and reduces N₂O from N fertilization. This study opened encouraging perspectives to the evaluation of sugarcane straw BC to improve soil quality and mitigate GHG emissions.

O produto sólido da pirólise, denominado "biochar" (BC) no contexto da melhoria nos atributos do solo como parte do manejo agrícola e ambiental, também tem se destacado na mitigação das mudanças climáticas. O pesquisador investigou os efeitos do BC nos atributos do solo, uso do nitrogênio (N) e emissões de GEE. No Cap. 1 comentou-se a origem do BC. No Cap. 2, caracterizou-se o BC de palha de cana-de-açúcar e avaliou-se o potencial de decomposição do C do solo, com os tratamentos: (T1) Solo; (T2) BC; (T3) Solo + BC 10 Mg ha^-1; (T4) Solo + BC 20 Mg ha^-1 (T4); e (T5) Solo + BC 50 Mg ha^-1. No Cap. 3, avaliou-se a combinação BC, torta de filtro (TF) e vinhaça (V) em atributos do solo e fluxos de dióxido de carbono (CO₂), metano (CH₄) e óxido nitroso (N₂O) nos tratamentos: (T1) Solo + TF + V; (T2) Solo + TF + V + BC 10 Mg ha^-1; (T3) Solo + TF + V + BC 20 Mg ha^-1; e (T4) Solo + TF + V + BC 50 Mg ha^-1. No Cap. 4 investigou-se a eficiência de uso do N num experimento em vasos com trigo usando NH₄ [¹⁵N]O₃ e doses de BC, com os tratamentos: (T1) Solo, com N, sem BC; (T2) Solo, com N, BC 10 Mg ha^-1; (T3) Solo, com N, BC 20 Mg ha^-1; e (T4) Solo, com N, BC 50 Mg ha^-1. Os teores de C e N do BC foram maiores comparado à biomassa. K, Mg e P totais também aumentaram. Os menores fluxos de CO₂ foram do BC. O CO₂ do solo e solo + BC não diferiram. Observou-se maior CO₂ - C4 no primeiro dia de incubação, porém sem diferenças no CO₂ - C3. O BC apresenta características para melhorar atributos do solo e reduzir as emissões de CO₂. No Cap. 3, pH, P e bases aumentaram e o Al³⁺ diminuíu com o BC. Os impactos do BC na CTC foram maiores em solo arenoso. O N mineral diminuíu com o BC. O CO₂ acumulado no T1 foi maior nos solos arenoso e argiloso comparado ao controle. O T2 e T3 aumentaram o CO₂ acumulado do arenoso relativo ao T1, enquanto T4 e T1 não diferiram. O BC reduziu as emissões de N₂O pelos solos arenoso e argiloso comparado ao T1. O BC combinado à TF e V afetaram pH, CTC, P e bases do solo arenoso. O BC suprimiu o N₂O de solos com V e TF. No Cap. 4, o BC diminuíu as emissões de N₂O comparado ao fertilizante N apenas. T4 teve rendimento de grãos superior ao T1. T2 a T4 apresentaram maior peso de 100 grãos e biomassa aérea. T3 e T4 tiveram maior N em grãos. O BC melhora o uso do N, a produção de grãos e reduz o N₂O de fertilizante N, abrindo perspectivas para a avaliação do BC de palha de cana-de-açúcar na melhoria da qualidade do solo e mitigar das emissões de GEE.