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Indian Black Earths (IBEs) are distributed throughout the Amazon. They are characterized by their high chemical fertility and agricultural potential. IBEs have high organic carbon, favouring the improvement of soil structure. This work aimed to evaluate the aggregates and organic carbon (OC) spatial variability in different IBEs in southern Amazonas. We evaluated the organic carbon spatial variability, mean weight diameter (MWD), soil bulk density (ρb) and aggregate classes under three uses of soil: pasture, cocoa, and coffee. We collected 528 soil samples in a point grid according to its use at two depths: 0.0-0.05 m and 0.10-0.20 m. Results were subjected to variance, descriptive, and geostatistical analyses. We concluded that the soil use influenced the IBEs physical attributes soil behavior, concentrating the higher values of CO, aggregates > 2.00 mm, and MWD at 0.0-0.05 m in relation to ρb and aggregates < 2.00 mm where the higher values were the ones at 0.10-0.20 m. Aggregates< 2.00 mm (0.10-0.20 m) and OC (0.0-0.05 m) did not show spatial dependence, while the class of aggregates > 2.00 mm was the only attribute which represented to be a natural characteristic of the soil, with a strong spatial dependence, independently the land use and depth. There was no spatial relationship between the attributes studied and the geomorphic diversity. As Terras Pretas de Índio (TPIs) encontram-se distribuídas por toda a Amazônia. Elas são caracterizadas pela alta fertilidade química e potencial agrícola. As TPIs possuem alto carbono orgânico, favorecendo a melhoria da estrutura do solo. Este trabalho teve como objetivo avaliar a variabilidade espacial dos agregados e do carbono orgânico (CO) em diferentes usos de TPIs no sul do Amazonas. Foi avaliado a variabilidade espacial do carbono orgânico, diâmetro médio ponderado (DMP), densidade do solo (ρb) e as classes de agregados sob três usos do solo: pastagem, cacau e café. Nas áreas estudas construiu-se um grid regular de pontos, de acordo com o uso do solo e nas profundidades, 0-0,05 m e 0,10-0,20 m, totalizando 528 amostras de solo. Os resultados foram submetidos à análise de variância, descritiva e geoestatística. O uso do solo influenciou o comportamento dos atributos físicos das TPIs, concentrando os valores mais altos de CO, agregados > 2.00 mm e DMP na profundidade 0,0-0.05 m em relação a ρb e agregados 2,00 mm foi o único atributo que representou uma característica natural do solo, com forte dependência espacial, independentemente do uso e profundidade do solo. Não houve relação espacial entre os atributos estudados e a diversidade geomórfica.

The conversion of native grassland into farmland causes changes in the soil. Tillage has profound effects on soil organic matter. The intensification of soil tillage decreases soil quality by reducing aggregate stability. Soil aggregate stability and soil organic matter are key indicators for soil quality and environmental sustainability in agro-ecosystems. The aim of the present study is to evaluate the total organic carbon content and the physical and chemical fractions of the organic matter in a soil under different uses and types of management over 27 years. Four soil tillage treatments with two annual crops were evaluated (no-tillage, NT; rotating tillage, RT; minimum tillage, MT; and conventional tillage, CT), as well as bare soil (BS) (standard plot of the Universal Soil Loss Equation - USLE) and natural grassland (NG) as a reference area. The experiment was carried out in an Inceptisol (Cambissolos) in southern Brazil. We determined total organic carbon (TOC) and particulate organic carbon (POC), and organic carbon associated with soil minerals (OCam). The chemical fractionation of carbon was into fulvic and humic acids, and humin. In addition, soil aggregates were divided into five size classes. The type of soil tillage affected the soil organic carbon content, namely TOC, POC, and OCam, as well as the composition of the physical and chemical fractions and their distribution in the arable soil layer. There was a positive relationship between stable aggregates and organic carbon in the soil: the higher the proportion of aggregates in class 1, the higher the organic carbon content. The results support the hypothesis that the carbon stock depends on intensification of a conservation tillage system with a continuous input of C through biomass, which maintains and supplies a continuous flow of C to the carbon transformation processes in the soil.

espanolEste estudio tuvo como objetivo medir las concentraciones de carbono (C), nitrogeno (N) y la abundancia natural de 13C y 15N en macro y microagregados en los sistemas de uso de la tierra. Tomamos muestras de las capas 0-5 y 5-10 cm en el sistema de siembra directa (NTS), sistema de labranza convencional (CTS), bosque secundario y pastizales en el Sur de Brasil. Se encontro mas grandes variaciones en las concentraciones de C y N para la clase agregados 8-2 mm, con la secuencia de pastos > bosque = NTS > CTS, en comparacion con la clase desde 0,25 hasta 0,105 mm. Ademas, se encontro que los valores de 13C mas negativos en los microagregados y el menos negativo se encontraron en los macroagregados. Arando y grada en el CTS causa la fractura de los agregados del suelo, lo que acelera las reacciones de mineralizacion de la materia organica del suelo (SOM) y desalentando la oclusion de SOM en los agregados, lo que resulta en valores 15N altos en comparacion con los demas sistemas evaluados. Las variaciones mas grandes en C y N de contenido para la clase de 8-2 mm y las variaciones mas pequenas de la clase 0,25 hasta 0,150 mm indican que hay mayor y menor sensibilidad al sistema de gestion adoptado en estas areas y la proteccion menor y mayor de la C y N por estas clases de agregados, respectivamente. EnglishThis study aimed to measure the concentrations of carbon (C), nitrogen (N) and the natural abundance of 13C and 15N in macro and microaggregates under systems of land use. We sampled the 0-5 and 5-10 cm layers in no-tillage system (NTS), conventional tillage system (CTS), secondary forest and pasture in southern Brazil. The largest variations of C and N concentrations were found for the 8-2 mm aggregate class, with the sequence pasture > forest = NTS > CTS, compared to the 0.25-0.105 mm class. The most negative δ13C values were found in the microaggregates and the least negative were found in the macroaggregates. Plowing and harrowing in the CTS cause the fracturing of soil aggregates, accelerating the mineralization reactions of soil organic matter (SOM) and discouraging the occlusion of SOM in the aggregates, resulting in higher δ15N values compared to the other systems evaluated. The larger variation in C and N content for the 8-2 mm class and smaller variation in the 0.25-0.150 mm class indicate that there is higher and lower sensitivity to the management system adopted in these areas and lesser and greater protection of the C and N by these aggregate classes, respectively.

This study aimed to measure the concentrations of carbon (C), nitrogen (N) and the natural abundance of 13C and 15N in macro and microaggregates under systems of land use. We sampled the 0-5 and 5-10 cm layers in no-tillage system (NTS), conventional tillage system (CTS), secondary forest and pasture in southern Brazil. The largest variations of C and N concentrations were found for the 8-2 mm aggregate class, with the sequence pasture > forest = NTS > CTS, compared to the 0.25-0.105 mm class. The most negative δ13C values were found in the microaggregates and the least negative were found in the macroaggregates. Plowing and harrowing in the CTS cause the fracturing of soil aggregates, accelerating the mineralization reactions of soil organic matter (SOM) and discouraging the occlusion of SOM in the aggregates, resulting in higher δ15N values compared to the other systems evaluated. The larger variation in C and N content for the 8-2 mm class and smaller variation in the 0.25-0.150 mm class indicate that there is higher and lower sensitivity to the management system adopted in these areas and lesser and greater protection of the C and N by these aggregate classes, respectively. Este estudio tuvo como objetivo medir las concentraciones de carbono (C), nitrógeno (N) y la abundancia natural de 13C y 15N en macro y microagregados en los sistemas de uso de la tierra. Tomamos muestras de las capas 0-5 y 5-10 cm en el sistema de siembra directa (NTS), sistema de labranza convencional (CTS), bosque secundario y pastizales en el Sur de Brasil. Se encontró más grandes variaciones en las concentraciones de C y N para la clase agregados 8-2 mm, con la secuencia de pastos > bosque = NTS > CTS, en comparación con la clase desde 0,25 hasta 0,105 mm. Además, se encontró que los valores de 13C más negativos en los microagregados y el menos negativo se encontraron en los macroagregados. Arando y grada en el CTS causa la fractura de los agregados del suelo, lo que acelera las reacciones de mineralización de la materia orgánica del suelo (SOM) y desalentando la oclusión de SOM en los agregados, lo que resulta en valores 15N altos en comparación con los demás sistemas evaluados. Las variaciones más grandes en C y N de contenido para la clase de 8-2 mm y las variaciones más pequeñas de la clase 0,25 hasta 0,150 mm indican que hay mayor y menor sensibilidad al sistema de gestión adoptado en estas áreas y la protección menor y mayor de la C y N por estas clases de agregados, respectivamente.