ABSTRACT The agricultural use of biochar has been the focus of much research in the last decade due to the improvement of soil chemical, physical, and biological attributes. Nonetheless, Brazil still has no specific legislation for biochar, limiting its agricultural use. The objective of the present work is to evaluate the use of biochar produced from spent coffee grounds (SCG) and coffee parchment (CP) by slow pyrolysis at 700 °C according to the existing framework of the Brazilian Ministry of Agriculture, Livestock, and Food Supply (MAPA) legislation for organic fertilizer, soil conditioner or plant substrate. Biochar was characterized according to normative instructions No. 17, 31, 61, 7, 5 and 35. Although not required by the addressed legislation, the semitotal content of macro- and micronutrients was also determined. While CP biochar could be used as an organic fertilizer or plant substrate, SCG biochar, due to its higher Ni content and lower than required cation exchange capacity (CEC), did not meet MAPA legislation criteria to allow for its agricultural use. Future regulations can be based on the current standards, and structural attributes, such as total C content, particle size distribution, and complete macro- and micronutrient determination should be included. Further research may also indicate the viability of biochar use as a soil conditioner based on a more representative set of biomasses with a higher CEC. These considerations will help to take advantage of the benefits of biochar to soil, contributing to a circular economy, which is still at a difficult stage in Brazil.

O objetivo deste trabalho foi avaliar, por meio de incubação anaeróbica, a mineralização e a disponibilidade de N em solos tratados com aplicações sucessivas de lodo de esgoto, e determinar o efeito residual das aplicações anteriores na taxa de mineralização do nitrogênio (TMN). Dois experimentos de longa duração foram realizados com doses anuais de lodo de esgoto, para o cultivo de milho: um com dose recomendada de lodo, correspondente a 120 kg ha-1 de N, e 2, 4 e 8 vezes essa dose, em área da Embrapa Meio Ambiente, em Jaguariúna; e outro com 80 kg ha-1 de N aplicado via adubo mineral, e 1 e 2 vezes a dose recomendada de lodo de esgoto, em área do Instituto Agronômico, em Campinas; além de testemunha, sem aplicação de lodo. A disponibilidade de N e a TMN foram estimadas em condições de campo e por incubações anaeróbicas em laboratório. O N total absorvido pelas plantas também foi determinado. O lodo de esgoto é mais efetivo em fornecer nitrogênio ao milho, em longo prazo, do que a adubação mineral. O efeito residual do lodo de esgoto não influencia a TMN do lodo recém-adicionado. O método de incubação anaeróbica é eficiente em estimar a mineralização do N proveniente de lodo de esgoto recém-adicionado.

The objective of this work was to evaluate, through anaerobic incubation, N mineralization and availability in soils treated with successive applications of sewage sludge, and to determine the residual effect of previous applications on nitrogen mineralization rate (NMR). Two long-term experiments were conducted with annual sewage sludge doses for corn cultivation: one with the recommended dose of sewage sludge, correspondent to 120 kg ha-1 N, and 2, 4, and 8 times the dose in area at Embrapa Meio Ambiente, in Jaguariúna, in the state of São Paulo, Brazil; and the other with 80 kg ha-1 mineral N fertilization, and 1 and 2 times the recommended dose of sewage sludge in area at Instituto Agronômico, in Campinas, in the state of São Paulo, Brazil; besides a control, without sewage sludge application. N availability and NMR were determined in field conditions and through anaerobic incubations in laboratory. Total nitrogen absorbed by plants was also estimated. Sewage sludge is more effective in supplying nitrogen to corn in the long term than mineral fertilization. The residual effect of sewage sludge does not influence the NMR from newly-added sludge. The method of anaerobic incubation is efficient in estimating the mineralization of N from newly-added sewage sludge.