Elias Mendes Costa

Soil fertility, physical and chemical organic matter fractions, natural 13C and 15N abundance in biogenic and physicogenic aggregates in areas under different land use systems

The dynamics of soil aggregation, including aggregate formation by biogenic and physicogenic processes, is affected by the soil management system. The present study aimed to divide soil aggregates into biogenic and physicogenic, and to characterise the aggregates in terms of soil exchange complex, distribution of total organic carbon (TOC), nitrogen (N) levels, and natural 13C and 15N abundance, and determine C levels in the soil organic matter (SOM) fractions of the aggregates. The areas studied were under a no-till system (NTS) established 15 years before, conventional tillage system (CTS) managed with ploughing and harrowing for 56 years, and a secondary forest (Forest) and pasture grass (Axonopus compressus) (Pasture) (both ≥30 years old). Undisturbed soil samples were collected at 0–5 and 5–10 cm. CTS was unsuitable for biogenic aggregate formation, and NTS and Forest areas showed similar biogenic and physicogenic aggregate content. The Pasture area promoted the formation of biogenic aggregates. In contrast to CTS, NTS increased TOC, calcium, magnesium, nitrogen and phosphorus levels. Considering the parameters evaluated, the Forest area showed the most variation (differences) between biogenic and physicogenic aggregates. Biogenic aggregates exhibited higher TOC and nutrient levels than their physicogenic counterparts. In the CTS area, the absence of legumes and the long-term and constant use of N-fertilisers resulted in 15N soil enrichment (at 0–5 cm). In the Pasture area, the absence of legumes and the constant deposition of cattle manure also increased 15N content relative to NTS and Forest areas. The Forest area had the lowest 15N values in the two layers and aggregate types studied. The levels of 13C reflect the type of material incorporated in the soil (mostly C3 plants in Forest and NTS areas and C4 plants in Pasture and CTS areas). The Pasture area favoured the formation of stable SOM, with higher levels of C content in humin fraction (C-HUM) and mineral-associated OC (MOC). CTS compromised SOM stabilisation, producing lower levels of C-HUM, MOC, and moderately oxidisable and resistant fractions. The biogenic aggregates enhanced soil fertility and contained higher C content in SOM fractions than the physicogenic aggregates. We conclude that biogenic rather than physicogenic aggregates can be considered reliable indicators of soil quality.

Mapping Soil Organic Carbon and Organic Matter Fractions by Geographically Weighted Regression

The soil organic matter (SOM) content and dynamic are related to vegetation cover, climate, relief, and geology; these factors have strong variation in space in the southeastern of Brazil. The objective of the study was to compare and evaluate performance of classical multiple linear regressions (MLR) and geographically weighted regression (GWR) models to predict soil organic carbon (SOC) and chemical fractions of organic matter in the Brazilian southeastern mountainous region. The regression models were fitted based on SOC and chemical fractions of SOM. The points ( = 89) were selected by pedologists experience along transects and toposequences. The covariates were also selected using the empirical knowledge of pedologists when choosing variables that drive soil carbon content and its dynamics. Geology map, legacy soils map, terrain attributes derived from digital elevation model, and remote sensing indices derived from RapidEye sensor bands were used as covariates. In all MLR models (except for fulvic acid fraction [FAF]), the legacy soil map was selected as a covariate by the stepwise approach. The geology map was not selected as important covariate to predict FAF and humin (HUM). At least one variable derived from remote sensing was selected by the adjusted models. For the prediction of the SOC, HUM, and FAF, the GWR models had the highest performance. The MLR models extrapolated the results, especially for SOC. The relationships among SOC, SOM fractions, and environmental covariates were affected by local landscape variability, and the GWR model was better at modeling.

Soil fertility, humic fractions and natural abundance of 13C and 15N in soil under different land use in Paraná State, Southern Brazil

El uso de lasfracciones humicas de la materia organica del suelo (MOS) y las mediciones isotopicas de 13C y 15N se puede utilizar para resaltar las diferencias entre los sistemas de gestion con diferentes intensidades de uso de la tierra. El estudio caracteriza la fertilidad del suelo, cuantifica los niveles de carbono en las fracciones humicas y evaluo la abundancia natural de 13C y 15N en el sistema de siembra directa (NTS), sistema de labranza convencional (CTS), bosque secundario y pastizales en el Sur de Brasil. NTS es mas eficaz en el aumento depH (0,0 a 0,10 m), niveles de Ca (0,0 a 0,05 m), P (excepto 0,05-0,10 m) y N (0,0 a 0,10 m); los estoques de carbono organico total (TOC) (0,0-0,20 y 0,0 a 0,40 m), y los niveles de carbono de la fraccion humina (C-HUM) en 0,0-0,40 m; carbono de la fraccion de acido fulvico (C-FAF) y acidos humicos (C-HAF) en 0,0-0,05 m, que el sistema de labranza convencional (CTS). El uso de hierbas, en NTS y pastizales, aumenta las reservas de TOC en comparacion con los otros sistemas de uso y manejo de suelos evaluados en 0,0-0,40 m. En la capa superior del suelo la influencia antropogenica de arar y desgarradora, en CTS promove una mayor perdida de carbono en C-HUM, C-FAF y C-HAF en comparacion con NTS, bosque y pastos. En CTS, el cultivo de maiz durante 42 anos despues de la eliminacion de la cubierta forestal no altero el 13C en 0,00,40 m. En pastos, la ausencia de legumbres, la deposicion constante de estiercol de ganado y una materia organica mas estable favorece a los niveles altos 15N (excepto en 0,0-0,05 m en CTS). La disminucion de los valores 15N en 0,0-0,10 a 0,10-0,20 m en CTS indica que la rotacion del suelo (por el arado y desgarradora) tiene el potencial para perturbar la variacion relacionada con la profundidad en el suelo 15N, acelerando su descomposicion y comprometiendo las transformaciones de N. Entre las variables analizadas, la determinacion del carbono en fracciones humicos y los valores de 15N son eficientes en la identificacion de cambios en el suelo producidos por el uso del suelo o de los sistemas de gestion.

Carbon, nitrogen and the natural abundance of 13C and 15N in macro and microaggregates

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.