Resumo -O objetivo deste trabalho foi verificar a influência de diferentes manejos no carbono orgânico e na estabilidade de agregados em um Latossolo Vermelho. Os seguintes tratamentos foram avaliados: PDs -plantio direto, por quatro anos, com a sucessão milho (silagem)/soja; PDg -plantio direto, por quatro anos, com a sucessão milho/milho/milho/soja; PDtf -três anos contínuos, com tifton (feno), e no quarto ano, soja sob plantio direto; SC -sistema convencional com soja, nos últimos quatro anos; e MN -mata nativa. A estabilidade de agregados foi expressa pelos índices: diâmetro médio ponderado, diâmetro médio geométrico, porcentagem de agregados maiores que 2,0 mm estáveis em água e índice de estabilidade de agregados. Em todos os tratamentos, houve diminuição da estabilidade de agregados com o aumento da profundidade. Os tratamentos cultivados tiveram seus índices de agregação reduzidos em relação à mata nativa. O sistema convencional apresentou os menores índices de agregação. O uso da gramínea perene tifton foi o tratamento que promoveu a melhor recuperação da estabilidade de agregados em água. Correlações significativas e positivas foram obtidas entre carbono orgânico total e os índices de estabilidade estudados.Termos para indexação: solos tropicais, cerrado, plantio direto, agregação. Organic carbon and aggregate stability of a Red Latossol under different managementsAbstract -The objective of this work was to verify the influence of different managements on organic carbon and on aggregate stability of a Red Latossol (Typic Haplorthox). The following treatments were appraised: PDsno tillage for four years with successions corn (silage)/soybean; PDg -no tillage for four years with the successions corn/corn/corn/soybean; PDtf -three years with tifton (hay) and soybean in the fourth year; SC -conventional cultivation with soybean in the last four years; and MN -native forest. The aggregate stability was expressed by the indexes: mean weight diameter, mean geometric diameter, percentage of stable aggregates >2.0 mm, and stable aggregates index. The aggregate stability in all the treatments decreased with depth. Indexes in cultivated treatments reduced in relation to native forest ones. The conventional system presented the worse indexes. Perennial grass tifton was the best treatment to recover aggregate stability. Significant positive correlations were obtained between total organic carbon and the studied aggregate stability indexes.

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Purpose The mineralization/immobilization of nutrients from the crop residues is correlated with the quality of the plant material and carbon compartments in the recalcitrant and labile soil fractions. The objective of this study was to correlate the quality and quantity of crop residues incubated in the soil with carbon compartments and CO 2 -C emission, using multivariate analysis. Materials and methods The experiment was conducted in factorial 4 + 2 + 5 with three replicates, referring to three types of residues (control, sugarcane, Brachiaria, and soybean), and two contributions of the crop residues in constant rate, CR (10 Mg ha −1 residue), and agronomic rate, AR (20, 8, and 5 Mg ha −1 residue, respectively, for sugarcane, soybean, and Brachiaria), evaluated five times (1, 3, 6, 12, and 48 days after incubation). At each time, we determined the CO 2 -C emission, nitrogen and organic carbon in the soil, and the residues. In addition, the microbial biomass and water-soluble, labile, and humic substance carbons fractionated into fulvic acids, humic acids and humin were quantified.Results and discussion Higher CO 2 -C emissions occurred in the soil with added residue ranging from 0.5 to 1.1 g CO 2 -C m −2 h −1 in the first 6 days of incubation, and there was a positive correlation with the less labile organic soil fractions as well as residue type. In the final period, after 12 days of soil incubation, there was a higher relation of CO 2 -C emission with carbon humin. The sugarcane and soybean residue (20 Mg ha −1 ) promoted higher CO 2 -C emission and the reduction of carbon residue. The addition of residue contributed to an 82.32 % increase in the emission of CO 2 -C, being more significant in the residue with higher nitrogen availability. Conclusions This study shows that the quality and quantity of residue added to soil affects the carbon sequestration and CO 2 -C emission. In the first 6 days of incubation, there was a higher CO 2 -C emission ratio which correlates with the less stable soil carbon compartments as well as residue. In the final period of incubation, there is no effect of quality and quantity of residue added to soil on the CO 2 -C emission.

Microbial activity and biochemical properties are important indicators of the impact of organic composting on soil. The objective of this study was to evaluate some indicators of soil microbial and biochemical processes after application of compost (household waste). A Typic Acrustox, sampled at a depth of 10 cm under Cerrado biome vegetation, was evaluated in three treatments: control (soil without organic compost amendment) and soil with two doses of domestic organic compost (10 and 20 g kg -1 soil). The following properties were evaluated: released C (C-CO 2 ): microbial respiration 15 days after incubation; microbial biomass C (MBC); total glucose (TG); metabolic quotient (qCO 2 ); and enzyme activity of β− β− β− β− β−glucosidase and acid and alkaline phosphatase. The application of household compost, at doses of 10 and 20 g kg -1 Typic Acrustox, resulted in significant gains in microbial activity, organic C and C stock, as evidenced by increased MBC and TG levels. On the other hand, qCO 2 decreases indicated greater microbial diversity and more efficient energy use. The addition of compost, particularly the 20 g kg -1 dose, strongly influenced the enzyme β− β− β− β− β−glucosidase and phosphatase (acid and alkaline). The β− β− β− β− β−glucosidase activity was significantly increased and acid phosphatase activity increased more than the alkaline. The ratio of β− β− β− β− β−glucosidase to MBC was greater in the control than in the composted treatments which suggests that there were more enzymes in the control than in the substrate or that the addition of compost induced a great MBC increase.Index terms: Cerrado, Soil respiration, microbial biomass, glucose, phosphatase, β− β− β− β− β−glucosidase.(