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Changes in land use have drastically reduced the Dry Chaco forests in central Argentina. In particular, conversion to crops has generated significant losses in soil organic carbon (SOC) and associated ecosystem services. On the other hand, less drastic changes in use, such as the conversion of forests to shrublands as a result of logging and grazing intensification, can also considerably affect the dynamics of the SOC. In this work, we evaluate total SOC, SOC in particulate organic matter (C-POM) and mineral-associated organic matter (C-MAOM), and potential microbial respiration from 0-10 cm of soil in four vegetal physiognomies resulting from logging and intensification of grazing. Total SOC content decreased by 73% in the most intensively used physiognomy (open shrubland) compared to the preserved forest. This was reflected in a decrease in C-POM (-85%), considered more sensitive to management, as well as in a decrease in C-MAOM (-54%), considered more stable. Land use intensification also decreased microbial activity by up to 62%. However, carbon losses from microbial respiration could be amplified due to reduced physical protection in intensively used vegetal physiognomies. Our results suggest that logging and grazing in Dry Chaco forests can generate significant alterations in SOC storage and stabilization, leading to soil degradation and loss of key ecosystem services. [ABSTRACT FROM AUTHOR]

Los cambios en el uso de la tierra han reducido de forma drástica los bosques del Chaco Seco del centro de la Argentina. En particular, la conversión de bosques a cultivos ha generado pérdidas significativas en el carbono orgánico del suelo (COS) y en los servicios ecosistémicos asociados al mismo. Por su parte, cambios menos drásticos en el uso, como la conversión de bosques a arbustales producto de la intensificación en la tala y la ganadería, también pueden afectar considerablemente la dinámica del COS. En este trabajo evaluamos el COS total, el COS presente en la materia orgánica particulada (C-MOP) y en la materia orgánica asociada a minerales (C-MOAM), y la respiración microbiana potencial de los 0-10 cm de suelo bajo condiciones controladas en cuatro fisonomías vegetales del Chaco Seco de Córdoba, resultantes de la intensificación en la tala y en la ganadería. El contenido de COS disminuyó un 73% en la fisonomía con mayor intensidad de uso (arbustal abierto) en relación con el bosque conservado. Esto se reflejó en una disminución del C-MOP (-85%), considerado más sensible al manejo, y en una disminución en el C-MOAM (-54%), considerado más estable. La intensificación en el uso también disminuyó hasta un 62% la actividad microbiana. Sin embargo, las pérdidas de carbono por respiración microbiana podrían intensificarse por una reducción de la protección física en las fisonomías vegetales con mayor uso. Nuestros resultados sugieren que la tala y el pastoreo en bosques del Chaco Seco pueden generar importantes alteraciones en el almacenamiento y en la estabilización del COS, lo que puede conducir a la degradación del suelo y a la pérdida de servicios ecosistémicos clave.

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Introduction: Coarse particulate organic matter originated in riparian vegetation is the main source of energy in many headwater streams. However, the transfer of such material is altered by the destruction of forests. Objective: To assess flow differences of this organic matter in streams with forests and grasslands. Methods: We compared input, storage and export of this organic matter in the riparian belts of streams with forests, and streams with grasslands, in the central Andean region of Colombia. For each stream, we measured vertical and lateral litter with baskets; stream bed litter with a quadrant, and matter export with drift nets, in a 100 m reach. Results: The streams with riparian forest received an average of 915 g m-2 of coarse particulate organic matter annually, exported a total of 334 g m-3 and stored 732 g m-2, values that were significantly higher than in grassland streams, where the corresponding values were: 125.4 g m-2; 128 g m-3 and 205.5 g m-2. Conclusions: The removal of tree cover from the riparian zone reduced the organic matter in these headwater streams of Colombia. [ABSTRACT FROM AUTHOR]

The Colombian horticultural area of eastern Antioquia is located on hillsides where lots of the productive capability of the soil has been lost due to the continuous tillage. The objective of the research was to determine the changes in the content of particulate organic matter (POM) and the mineralogy of an Andisol in six conditions of soil management, in Marinilla (Antioquia, Colombia). In split plots, the soil sample was taken in each situation, with three replications per treatment, in plots of virgin soil (VS) with 5, 10, and 20 years of conventional tillage (CT), and 5, 10 years of fallow (F). It was sampled with an auger to 0.2 m depth. In each sample the POM was quantified: chemical analyzes were carried out (pH, Mg, K, P, S) and physical (total porosity, bulk density, and mean weight diameter (MWD) of water-stable). The POM was sensitive to the tillage processes, decreasing by 35 % after 5 years and 75 % after 10 years, in relation to the virgin soil (VS). The POM was increased significantly during the first 5 years of fallow in relation to CT soils. The POM and MWD showed a logarithmic relationship (R2 = 0.80), which indicates the influence of the POM on the stable aggregates and on the physical fertility of the soil. In short time, the dynamics of OM with the amorphous oxides of Fe and Al have affected the mineralogy of the clay fraction due to soil management. [ABSTRACT FROM AUTHOR]

La aplicación de compost mejora la fertilidad del suelo y el crecimiento de los cultivos, sin embargo, es aún escasa la información sobre la aplicación de compost de cama profunda porcina (CPP) en soja. El objetivo de este estudio fue evaluar el impacto de la aplicación de CPP sobre propiedades de un suelo Argiudol Típico y producción de un cultivo de soja. Se utilizó un diseño completo aleatorizado con dos tratamientos y tres repeticiones: aplicación de compost de CPP (14 t ha-1-154 kg N ha-1) comparado con un testigo sin aplicación. La aplicación de compost provocó incrementos en la materia orgánica particulada (MOP), carbono de la biomasa microbiana (CBM) (p

Los cultivos puente verde (CPV) inciden sobre el suelo y el cultivo posterior según su tipo y cómo se descomponen sus residuos. Se hipotetizó que 1) los residuos de CPV gramíneas se descomponen a menor tasa que los de leguminosas; 2) la descomposición de CPV leguminosas genera mayor y más rápida disponibilidad de nitrógeno (N); y 3) las fracciones orgánicas lábiles del suelo aumentan más y más tarde con CPV gramíneas y con los residuos en superficie. Se realizó un experimento sobre un Argiudol típico con CPV avena (Avena sativa L.), vicia (Vicia villosa Roth.) y un testigo sin CPV (TE). Se colocaron iguales cantidades de residuos picados de ambos CPV en superficie y enterrados. Se tomaron muestras de 0-20 cm en 7 momentos en 133 d para determinar: carbono (C) remanente de residuos (CR), C orgánico total (COT) y particulado (COP), N de amonio liberado en anaerobiosis (NAN) y N de nitrato (N-NO3 -). El CR de los residuos enterrados disminuyó a mayor tasa y sin diferencia entre avena y vicia. En superficie, la vicia se descompuso más rápido que la avena y a los 133 d se había descompuesto 60 y 79% de sus residuos, respectivamente. COT y COP fueron mayores luego de avena (75,1 y 18,6 Mg ha-1, respectivamente) que luego de vicia y TE (70,4 y 16,8 Mg ha-1, respectivamente). También fueron menores con los residuos enterrados (69,7 y 15,9 Mg ha-1, respectivamente) que cuando quedaron en superficie (73,3 y 18,9 Mg ha-1, respectivamente). La posición de los residuos no afectó el NAN, pero fue mayor luego de avena y vicia (63,1 mg kg-1) que del TE (50,2 mg kg-1). COT, COP y NAN mostraron escasa variación durante el ensayo. Hasta los 49 d, el N-NO3 - aumentó (45 a 108 kg ha-1) y fue mayor cuando el CPV fue vicia. No se reunieron evidencias suficientes para rechazar la primera y segunda hipótesis, pero sí para rechazar la tercera.

Relief is a soil formation factor that can modify the distribution of soil organic matter (SOM) fractions in a landscape. The objective of this study was to evaluate the effect of the relief on SOM fractions, considering their distribution in different topographic positions, segments, in two pedoforms (concave and convex) in areas covered with forest in the Atlantic Forest biome. The two pedoforms were selected in adjacent areas and divided into segments considering the topographic variation. The carbon and nitrogen origins were evaluated in the extract up to 100 cm of depth. Soil samples from the 0-5, 5-10, and 10-20 cm layers were collected for chemical characterization and fractioning (granulometric and chemical) of the SOM. The soil density in the 0- 5 and 5-10 cm layers was determined to calculated the carbon stocks. The isotopic composition showed predominance of 13C. The highest organic carbon and particulate carbon contents were found in the convex pedoform. The distribution of humic fractions showed that the larger part of the humidified carbon was in the humin fraction. The humin and fulvic acid fractions were higher in the convex pedoform. The carbon stocks were, in general, higher in the convex pedoform, decreasing as the soil depth increased; and nitrogen stocks presented no differences. The higher carbon and nitrogen contents were found in the convex pedoform and in the lower region of the concave pedoform. [ABSTRACT FROM AUTHOR]

Los contenidos de carbono (C) orgánico total (COT) y particulado (COP) del suelo disminuyen con los años bajo agricultura y su variación afecta muchos procesos edáficos que determinan la productividad (e.g. la provisión de nitrógeno (N)). Las variaciones de COT y COP son dependientes del balance entre los aportes y la pérdida de C del suelo. Se hipotetiza que en molisoles del Sudeste Bonaerense: i) los cambios en COT y COP en la capa arable, son más dependientes del aporte carbonado de la secuencia de cultivos utilizada que del sistema de labranza (SL) empleado, ii) el contenido de COP es dependiente de las características de los residuos devueltos por el cultivo antecesor inmediato, y iii) las variaciones de COT y COP se relacionan con la capacidad del suelo de proveer N, independientemente del SL y de la secuencia de cultivos. Se determinaron el COT y el COP de muestras tomadas anualmente de 0-5 y 5-20 cm de un ensayo en Balcarce entre 2005 y 2011. El ensayo comprendió dos SL (convencional (LC) y siembra directa (SD)) y tres Secuencias de cultivos (con tres alternativas (Series) cada una), incluyendo maíz (M), trigo (T) y soja (S): MMT, MST y SST. El M y el T fueron fertilizados con N (FN). Hubo disminuciones diferenciales en COT y COP entre SL (sin disminución bajo SD y con disminuciones de 0,34 y 0,39 Mg ha-1 año-1 bajo LC, respectivamente) sólo en la capa de 0-5 cm. En la capa arable completa, aquellas variables disminuyeron con los años de agricultura (0,30 y 0,26 Mg ha-1 año-1, respectivamente), independientemente del SL. No se observó una disminución diferencial de COT ni de COP asociada a las combinaciones de cultivos, independientemente del SL. Tampoco se observó un efecto de las características del cultivo antecesor inmediato sobre el contenido de COP. Asimismo, el COT y el COP presentaron una dinámica similar a la reportada para NAN. No obstante, las relaciones entre NAN y COT y NAN y COP, si bien fueron significativas, presentaron bajos R² (0,55 y 0,57 (0-5 cm), 0,09 y 0,10 (5- 20 cm), 0,18 y 0,17 (0-20 cm), respectivamente). La FN (frecuencia, dosis) puede haber enmascarado los efectos esperados en la relación del COP y COT con el aporte de C por los residuos y, además, de aquéllas con el NAN, por afectar las condiciones de descomposición y transformación de los materiales orgánicos. Las evidencias reunidas no sostuvieron las hipótesis planteadas.

Reservoirs emit greenhouse gases (GHGs) as a result of flooded organic matter biodegradation after the filling process or the organic matter that enters through the tributaries. Hence, it is important to take an inventory of greenhouse gas emissions in the reservoirs, so that, measures can be established to minimize the impact of global warming. These gases are produced by anaerobic or aerobic processes occurring in reservoirs. In this work, the formation rates of carbon dioxide (CO2) and methane (CH4) in anaerobic reactors in batch were evaluated at laboratory scale, using water and plant material from the Topocoro reservoir, located in the department of Santander-Colombia. The results showed degradation rates of 0.5843 mg O2/L.d and 0.1269 mg O2/L.d for dissolved and particulate organic matter respectively. Furthermore, gas emissions after completing the degradation time were 0.6269 mg CH4/L and 31.2443 mg CO2/L. It was implemented a linear model to predict the formation of CO2 and an exponential model to predict the formation of CH4 with determination coefficients of 0.9999 and 0.9928 respectively. [ABSTRACT FROM AUTHOR]

Las emisiones de gases efecto invernadero asociadas al carbono orgánico del suelo (COS) son importantes para estudiar cambios en los ecosistemas terrestres. Hay modelos simples que, ofrecen la oportunidad de analizar la dinámica de las alteraciones provocadas por los cambios en el uso de suelo, la vegetación y las prácticas de manejo. En México se dispone de información del COS total y la textura del suelo. En el presente trabajo se analizan diferentes esquemas para parametrizar el modelo COLPOS, el cual se desarrolló para caracterizar la distribución del COS en fracciones físicas del suelo. El modelo considera el COS de diferentes almacenes: materia orgánica particulada (MOP, materia orgánica lábil) y complejos organominerales (MO + arena-limo-arcilla). El carbono orgánico inerte (COI), con tiempos medios de residencia de cientos a miles de años, y el tamaño de partícula asociado, permiten precisar los parámetros del modelo COLPOS y determinar las pérdidas potenciales de carbono orgánico del suelo. La validación de los métodos de parametrización del modelo COLPOS permite su implementación operativa empleando solamente la información disponible en México (COS y textura del suelo). La parametrización se desarrolló con base en los datos de experimentos de distribución del carbono asociadas al fraccionamiento físico de los suelos, después de la aplicación de dispersión ultrasónica para lograr fraccionamientos completos.

Green bridge crops (CPV) effect on soil and succeeding cash crops depends on the type of CPV and on how their residues decompose. We hypothesized that 1) decomposition rate of grass CPV is lower than that of legume CPV; 2) decomposition dynamics of CPV legume will lead to a higher and faster availability of nitrogen (N); and 3) residue decomposition will lead to a higher but delayed increase of labile soil organic matter fractions with grass CPV and when located on soil surface. We carried out an experiment on a Typic Argiudoll with CPV with oats (Avena sativa L.), vetch (Vicia villosa Roth.) and a control without CPV (TE). Equal amounts of chopped residues of both CPV were placed on surface and mixed with soil (buried). We took soil samples at 0-20 cm in 7 moments along 133 days to determine remnant residue (CR), carbon (C), total (COT), and particulate organic C (COP), ammonium N freed in anaerobiosis (NAN), and nitrate N (N-NO3 -). Remnant C of both CPV decreased over time, but at a higher rate when buried with differences between vetch and oats. On surface, vetch residues decomposed faster than oats residues, at the end of the experiment, 60 and 79% of the residues, respectively, had decomposed. Neither COT, COP, nor NAN changed along the experiment. After oats, COT and COP (75.1 y 18.6 Mg ha-1, respectively) were higher than after vetch and TE (70.4 y 16.8 Mg ha-1, respectively). Besides, these were lower when residues were buried (69.7 y 15.,9 Mg ha-1, respectively) than when residues were left on surface (73.3 y 18.9 Mg ha-1, respectively). The position of residues did not affect NAN, but it was higher after oats and vetch (63.1 mg kg-1) than after TE (50.2 mg kg-1). Up to 49 days from the start of the experiment there was an increase of N-NO3 - (45 up to 108 kg ha-1). N-NO3 - was higher when CPV was vetch and there was no difference between oats and TE. We did no collect enough evidence to reject the first and the second hypothesis, but evidences were enough to reject the third one. [ABSTRACT FROM AUTHOR]

A qualidade do solo em plantio direto está relacionada ao sistema de culturas e pode ser avaliada pelo teor de matéria orgânica particulada (>53 ∝m), em razão da funcionalidade que essa fração proporciona ao solo e à sua sensibilidade às diferenças de manejo. Visando estudar a qualidade do solo em sistemas de culturas em plantio direto, este trabalho foi conduzido em experimento de longa duração (21 anos) em Latossolo Vermelho distrófico típico nos Campos Gerais do Paraná. Seis sistemas de culturas foram avaliados, em que trigo-TR (Triticum aestivum L.), soja-SO (Glycine max L.), milho-MI (Zea mays L.), aveia-preta-AV, para cobertura (Avena strigosa Schreb.), ervilhaca-ER, para cobertura (Vicia villosa Roth); azevém-AZ, para feno (Lolium multiflorum Lam.); ou alfafa-AL, para feno (Medicago sativa L.) compuseram os seguintes sistemas: TR-SO (referência), ER-MI-AV-SO-TR-SO, ER-MI-TR-SO, AV-MI-TR-SO, AZ-MI-AZ-SO e AL-MI (milho a cada três anos). Os estoques de carbono orgânico total (COT), nitrogênio total (NT) e de C e N na matéria orgânica (MO) particulada (>53 µm) e associada aos minerais (

Soil total (COT) and particulate (COP) organic carbon (C) contents decrease over the years under cropping. Its variation affects many soil processes that determine soil productivity (e.g. nitrogen (N) supply). COT and COP changes depend on the balance between C input and loss. For mollisols of the southeastern region of Buenos Aires province, it was hypothesized that: 1) COT and COP content decrease in the arable layer and vary as a function of the crop sequence regardless of the tillage system (SL), ii) COP content depends on the immediate preceding crop residue characteristics, and iii) changes in COT and COP are related to the soil N supplying capacity, regardless of the SL and crop sequence. Total organic C and COP were determined in soil samples taken annually at 0-5 cm and 5-20 cm depths in a long-term experiment in Balcarce between 2005 and 2011. The experiment comprised two SL (conventional (LC) and no-till (SD) and three crop sequences (with three alternatives (Series) for each one), including corn (M), wheat (T) and soybean (S): MMT, MST y SST. Corn and T were fertilized with N (FN). There were differential decreases in COT and COP among SL (no decrease under SD and decreases of 0.34 and 0.39 Mg ha-1 yr-1 under LC, respectively) only at the 0-5 cm layer. In the whole arable layer COT and COP decreased over the years under cropping (0.30 and 0.26 Mg ha-1 yr-1, respectively), regardless of the SL. No differential COT nor COP decrease was detected related to crop sequences, regardless of the SL. Neither was there an effect of the immediately preceeding crop residue characteristics on COP content. Likewise, COT and COP showed similar dynamics than reported for NAN. Relationships between NAN and COT and NAN and COP were significant although with low R2 (0.55 and 0.57 (0-5 cm), 0.09 and 0.10 (5-20 cm), 0.18 and 0.17 (0-20 cm), respectively). Frequency and rate of FN may have masked the expected effects of the amount of residue C input on COT and COP and, besides, on the relationship of these two variables and NAN. Nitrogen fertilization affects organic material decomposition and transformation dynamics. The experimentally obtained evidences did not support the posed hypotheses. [ABSTRACT FROM AUTHOR]

El tipo de materia orgánica presente en el agua residual influye sobre el grado y la complejidad del tratamiento biológico, por lo que el análisis del fraccionamiento de la materia orgánica puede brindar información complementaria para la optimización de los procesos. En esta investigación, se identificaron las fracciones de materia orgánica: biodegradable particulada, biodegradable soluble, no biodegradable particulada y no biodegradable soluble, en el agua residual de una industria papelera y en los efluentes de las unidades que componen la planta de tratamiento de agua residual (clarificador primario, laguna aireada facultativa y laguna de sedimentación). Los resultados mostraron que la fracción no biodegradable representó el 69% de la DQO total del afluente, mientras que la fracción biodegradable significó el 31%. La clarificación primaria desempeñó un papel fundamental en la tratabilidad biológica del agua residual, al reducir significativamente la fracción no biodegradable. La laguna aireada facultativa disminuyó, representativamente, la fracción biodegradable soluble de 44% a 12%, mientras que la laguna de sedimentación desarrolló un efecto de pulimiento sobre el efluente, alterando, principalmente, la fracción particulada. La disminución de la materia orgánica no biodegradable soluble fue especialmente obtenida como resultado de su adsorción sobre la biomasa en la laguna aireada facultativa; la fracción de este tipo de materia orgánica fue adquiriendo mayor protagonismo en el agua residual, a medida que avanzó el grado de tratamiento, incrementado su valor desde 19%, en el afluente, hasta 45%, en el efluente de la laguna de sedimentación.Slowly biodegradable organic matter represents the bulk of organic matter content of pulp and paper mill wastewater which can influence the performance of treatment systems. The organic matter fractionation is a useful tool that generates information for optimize treatment processes of wastewater. Organic matter fractionation study was carried out. Biodegradable soluble, biodegradable particulate, non- biodegradable soluble and non-biodegradable particulate fractions were identifies in effluents of primary clarifier, facultative aerated pond and sedimentation pond. Results of this study show that organic matter non-biodegradable/ total organic matter ratios of the influent were 69% while biodegradable fraction was 31%. Primary clarifi�er removed significantly the non-biodegradable fraction it was key for biological treatment. The biodegradable soluble fraction was mostly removed in facultative aerated pond (44% to 12%). The effluent was polished in the sedimentation pond, mainly particulate organic matter fraction. Only a small percentage of non-biodegradable organic matter was adsorbed by facultative aerated pond biomass, the fraction of this organic matter accounted for 19% in the influent and increased to 45% in the effluent.

El contenido de carbono orgánico (CO) del suelo determina muchas de sus funciones en el agroecosistema, entre las que se destaca su capacidad de proveer nutrientes como el nitrógeno (N). El contenido de las fracciones de CO y de N mineralizable y su distribución en la masa del suelo dependen de las prácticas de manejo. El objetivo de este trabajo fue analizar el contenido de CO total (COT), asociado a la fracción mineral (COA) y particulado (COP) y del N mineralizable (a través del N liberado por incubación anaeróbica, NAN) en la masa total del suelo y en macro- y microagregados, bajo distintos sistemas de cultivo (pasturas y agricultura con labranza convencional (LC) y bajo siembra directa (SD) y fertilización con N (0 y 120 kg N ha-1). Se muestreó un ensayo de larga duración de rotaciones mixtas y labranzas en Balcarce, provincia de Buenos Aires. Se separaron macro- y microagregados por tamizado en seco y se determinaron los contenidos de COT, COA, COP y NAN en la masa del suelo y en cada fracción de agregados. Los suelos bajo pastura mostraron en general los mayores contenidos de todas las fracciones de CO y de NAN tanto en masa total como en cada fracción de agregados. Por otro lado, los niveles de todas esas variables fueron más bajos cuanto más prolongado fue el período bajo agricultura y bajo LC respecto a SD. No hubo diferencias entre tratamientos en la proporción de macro- y microagregados, pero sí hubo una relación significativa de los contenidos de COT y de COP en macroagregados con su estabilidad en situaciones de escaso disturbio (pasturas y SD). Bajo LC tal relación no fue significativa, y la estabilidad de agregados fue más baja. El NAN en la masa total de los suelos bajo agricultura, se relacionó significativamente con el NAN en los macroagregados y, por tanto, se puede esperar una mayor expresión del potencial de mineralización de N en situaciones de manejo que tiendan a romper los macroagregados o en las que éstos sean menos estables. No obstante, estos resultados indican que un manejo cuidadoso del suelo permitiría aprovechar a través del laboreo el servicio ecológico de la provisión de N con una mínima afectación de sus propiedades, dado que las diferencias entre situaciones bajo agricultura tanto en agregación como en las fracciones de CO y en NAN fueron bajas y los efectos se revirtieron con la inclusión de pasturas en la rotación.Soil organic carbon (CO) content determines many soil functions in the agroecosystem, including nitrogen (N) supply to crops. The level and distribution of organic carbon fractions and mineralizable N in the soil depends on management practices. The aim of this work was to analyze total organic carbon content (COT) associated with the mineral (COA) and particulate (COP) fraction and mineralizable N (through N release during anaerobic incubation, NAN) in whole soil and in macro- and microaggregates under different cropping systems (pastures and cropping with conventional tillage (LC) and with no-tillage (SD)) and N fertilization (0 and 120 kg N ha-1). Soil samples were taken from a long-term crop rotation and tillage system trial at Balcarce, Buenos Aires province. Macro- and microaggregates were separated by dry sieving and COT, COA, POC, and NAN content were determined in whole soil and in each aggregate fraction. The soils under pasture showed the highest CO fraction and NAN content both in whole soil and in each of the aggregate fractions. The longer the period under cropping and LC, the lower the variables compared with the SD regime. Although the proportion of macro- and microaggregates did not vary among treatments, a significant correlation was found between COT and POC content in macroaggregates and their stability when soil was less disturbed (pastures and SD). Under LC, aggregate stability was lower and there was no correlation with CO content. Under cropping there was a significant correlation between NAN in whole soil and NAN in the macroaggregates. A higher expression of N mineralization potential can therefore be expected in soils under management techniques that tend to break up macroaggregates or where these are less stable. However, the lack of significant differences in aggregation and in NAN and CO fractions under cropping suggests that careful tilling can help N mineralization largely without affecting its properties and that the inclusion of pastures in the rotation would reverse the effect of cropping.

Os resultados do fracionamento granulométrico da matéria orgânica do solo (MOS) podem contribuir para o entendimento da sua dinâmica em áreas com sistemas de manejo orgânico. O objetivo deste trabalho foi avaliar as frações granulométricas da MOS e o carbono orgânico total em áreas submetidas a manejo orgânico sob diferentes sistemas de uso do solo. As áreas selecionadas apresentavam os seguintes sistemas: preparo convencional (PC, milho/feijão), plantio direto (PD, beringela/milho), consórcio maracujá - Desmodium sp, uma área cultivada com figo e um sistema agroflorestal (SAF). As amostras de solo foram coletadas em duas profundidades (0-5 e 5-10cm) e duas épocas (verão - 17 de novembro de 2005 e inverno - 23 de junho de 2006-). Foi medido o carbono orgânico total (COT), calculado seu estoque e realizado o fracionamento granulométrico da MOS, obtendo-se o carbono orgânico particulado (COp) e o carbono orgânico associado aos minerais (COam). As áreas com figo e beringela/milho apresentaram os maiores teores de COT e estoques de COT na estação do verão. No inverno, os sistemas com rotação de culturas (PD e PC) foram mais eficientes no estoque de COT que os demais sistemas avaliados. Maiores variações foram observadas nos teores de COT na profundidade de 5-10cm, decorrentes dos sistemas de manejo adotados. Pelos valores de COp foi possível identificar diferenças entre todos os sistemas de uso avaliados na estação do verão e na profundidade de 0-5cm, destacando-se a área em plantio direto com os maiores valores, nas duas estações. O COp mostrou-se mais eficiente que o COT no verão para evidenciar diferenças entre os sistemas avaliados na profundidade de 0-5cm. As diferenças observadas entre os sistemas de manejo para o COam foram atribuídas ao uso constante da adubação orgânica.The soil organic matter (SOM) granulometry fractioning can contribute to the understanding of the SOM dynamics in areas under organic production systems. The objective of this study was to evaluate the granulometry fractions of SOM and total organic carbon in areas with organic management systems and under different soil usages. The selected areas presented the following systems: conventional tillage (CT, corn/beans), no tillage (NT, eggplant/corn), passion fruit and Desmodium sp consortium, fig grove, and agroforest system (AFS). Soil samples were taken in two depths (0-5 and 5-10cm) and two periods of the year (17/11/2005 - summer and 23/06/2006 - winter). The total organic carbon (TOC) was evaluated, and calculated the TOC stocks. The SOM was granulometrically fractioned, obtaining the particulate organic carbon (POC) and organic carbon associated to minerals (OCam). The fig grove and eggplant/corn areas presented the highest TOC and TOC stocks in the summer season. In the winter the crop rotation (NT and CT) systems were more efficient in the stocking of TOC that the other systems. There were observed highest TOC variations in the 5-10cm depth, resulting from the management systems adopted. From the POC values it was possible to identify differences among all systems evaluated, in the summer season and in the 0-5cm depth, standing out the area with no tillage, which showed the highest values, in the two seasons. The POC was more efficient than the TOC, in the summer, to evidence differences among the evaluated soil usage systems, in the 0-5cm depth. The differences observed among the production systems for OCam were attributed to the constant usage of organic manure.

El carbono orgánico (CO), componente clave del cual dependen muchas de las propiedades del suelo, está compuesto por fracciones lábiles, CO particulado (COP), y menos lábiles. El COP es un indicador temprano de los cambios en el CO provocados por las prácticas de manejo. Por otro lado, el N anaeróbico (Nan) es un indicador de la capacidad del suelo de mineralizar N. El objetivo de este trabajo fue evaluar el efecto de la siembra directa (SD), de la labranza convencional (LC) y de la fertilización nitrogenada sobre los contenidos de CO total (COT), COP, N orgánico (NO) total (NOT), NO particulado (NOP) y Nan, y su relación con el rendimiento de maíz. Se analizaron muestras de suelo (0-5 y 5-20 cm) de dos sectores de un ensayo iniciado en 1997 sobre Molisoles de Balcarce. Bajo SD hubo mayor concentración de COP, NOP, COT y NOT que bajo LC, principalmente en los primeros centímetros del suelo. En general, no hubo diferencias en el Nan entre sistemas de labranza. La fertilización no afectó los contenidos de las fracciones de CO y NO ni el de Nan. Tampoco se observaron relaciones significativas entre ellos y los rendimientos y la respuesta del maíz a la fertilización. Los elevados contenidos de CO y los altos aportes de C por los residuos pudieron haber sido las causas de que no se manifestaran las diferencias esperadas. Los resultados y tendencias observadas estarían indicando que en el futuro, aquéllas podrían manifestarse.The organic carbon (CO) is a key component that determines many soil properties, and it is composed of labile (particulate CO, COP) and less labile fractions. Particulate CO is an early indicator of changes in CO due to management practices. On the other hand, anaerobic N (Nan) is an indicator of the soil capacity to mineralize N. The objective of this study was to evaluate the effect of no-tillage (SD), conventional tillage (LC) and N fertilization on total CO (COT), COP, total organic N (NOT), particulate organic N (NOP), and of Nan contents, and on their relationship with corn yield. Soil samples (0-5 and 5-20 cm-depths) were taken from two areas of a long term experiment started in 1997 on a Mollisol in Balcarce. There was greater concentration of COP, NOP, COT and NOT under SD compared to LC, especially in the soil surface layer. In general, there were no differences in Nan content between tillage systems. Nitrogen fertilization did not affect either CO and NO fractions or Nan contents. There were no significant relationships between the latter and corn yield or corn response to N fertilization. High CO contents and C returns through crop residues in both tillage systems could have caused the lack of differences expected. The observed results and trends would indicate that significant differences between tillage systems could be manifested in the near future.

Soluções de iodeto de sódio (NaI) e de politungstato de sódio (PTS) têm sido utilizadas, de forma indistinta, no fracionamento densimétrico da matéria orgânica (MO) do solo. O objetivo deste estudo foi avaliar o efeito desses dois produtos em soluções de mesma densidade (1,80 kg L-1), bem como do aumento da densidade da solução de PTS (2,0 e 2,2 kg L-1), na obtenção de C na fração leve (FL) da MO do solo. As características estruturais da FL obtida com as diferentes soluções também foram avaliadas por ressonância magnética nuclear do 13C (RMN-13C) neste estudo, o qual foi realizado com amostras da camada de 0-5 cm de dois solos brasileiros (PVd-Argissolo Vermelho e LVd-Latossolo Vermelho). A dispersão do solo foi realizada com ultra-som (250 J mL-1 no PVd e 450 J mL-1 no LVd); a suspensão de 20 g de solo e 80 mL-1 de solução foi centrifugada (2.000 g, 90 min), e a FL, obtida pela filtragem do sobrenadante em filtro de fibra de vidro, sendo o C desta fração analisado por combustão seca (Shimadzu TOC-V CSH). O uso da solução de PTS aumentou a recuperação de C da FL em 152 % no PVd e em 166 % no LVd, em comparação à solução de NaI de mesma densidade (1,8 kg L-1). O incremento da densidade da solução de PTS também aumentou a obtenção de C na FL, o qual foi mais expressivo na densidade de 1,8 para 2,0 kg L-1 (57 % em ambos os solos) do que de 2,0 para 2,2 kg L-1 (21 % no PVd e 5 % no LVd). Com base nos teores de Fe e C da fração argila, estimou-se que a contaminação da FL com C da fração argila, quando do uso das soluções de PTS, variou de 1,9 a 3,5 % no LVd e de 6,8 a 10,4 % no PVd, os quais foram considerados baixos perante o alto percentual de incremento na recuperação de C na FL. O incremento da razão C Alquil/C-O-alquil e do C-carbonila na análise de RMN-13C sugere incremento na recuperação de FL em estádios mais avançados de decomposição com o uso de PTS e incremento da densidade da solução, tendo sido esses resultados mais expressivos no LVd. Com base no incremento da obtenção de C e na baixa contaminação da FL com C da fração argila, recomenda-se o uso da solução de PTS 2,0 kg L-1 em estudos de fracionamento densimétrico da MO do solo.Sodium iodide (NaI) and sodium polytungstate (SPT) solutions are being indistinctively used in density fractionation procedures of soil organic matter (SOM). This study aimed to evaluate these two solutions, adjusted to a density of 1.8 kg L-1 (NaI-1.8 and SPT-1.8), and particularly of SPT adjusted to densities of 2.0 (SPT-2.0) and 2.2 kg L-1 (SPT-2.2), with regard to their capacity of recovering the light fraction (LF) of SOM. A 20 g soil sample of the 0-5 cm layer of an Acrisol (PVd) and of a Ferralsol (LVd) was dispersed by sonication at 250 J mL-1 and 450 J mL-1, respectively for each soil, in 80 mL NaI or SPT solution. After centrifugation (2.000 g, 90 min), the LF in the supernatant was recovered on a fiberglass filter, dried and analyzed for C content determination (TOC dry combustion) and chemical structure characterization (13C nuclear magnetic resonance spectroscopy). The SPT-1.8 increased LF-C recovery by 152 % in the PVd and 166 % in the LVd, compared to NaI-1.8. Besides, the higher SPT-2.0 density increased LF-C recovery by 57 % in both soils as compared to SPT-1.8. Furthermore, SPT-2.2 recovered 21 % and 5 % more LF-C than SPT-2.0, in the PVd and LVd, respectively, but this additional recovery was not as pronounced as when density was changed from 1.8 to 2.0 kg L-1. Based on data of Fe content in LF and C and Fe content in clay fraction, we estimated that the contamination of clay-C in the LF using SPT solutions varied 1.9-3.5 % in the LVd and 6.8-10.4 % in the PVd. Theses values were considered low compared to the high increments obtained in LF-C recovery. The increases in both alkyl-C/O-alkyl-C ratio and carbonyl-C abundance when NaI was substituted by SPT and when SPT densities increased, suggested that more decomposed LF material was recovered, which was more evident in the LVd. Based on our results, we suggest using SPT solution adjusted to a density of 2.0 kg L-1 in studies focusing on densimetric fractionation of SOM.

Nuestro objetivo fue evaluar el efecto de siete sistemas de cultivo (SC) en un experimento de larga duración: pastura permanente (PP), agricultura permanente bajo siembra directa (SD) (SD100) y labranza convencional (LC) (LC100), rotación agricultura pastura (50%-50% del tiempo) bajo SD (SD50) y LC (LC50), rotación agricultura pastura (75%-25% del tiempo) bajo SD (SD75) y LC (LC75) y dos dosis de fertilización nitrogenada: 0 y 120 kg N ha-1, sobre el carbono orgánico total (COT) y particulado (COP), para 0-20 cm en 1994 y para 0-5, 5-20 y 0-20 cm de profundidad en 2003. En 1994, los mayores COP y COT se asociaron a manejos con períodos agrícolas previos cortos. En 2003, se encontraron diferencias entre SC en COT en la capa de 0-5 cm de profundidad, siendo PP, LC50 y SD50 los tratamientos con mayor COT. El COP fue más alto bajo PP, LC50 y SD50 a 0-5 y 0-20 cm de profundidad. A 0-5 cm COP bajo SD fue significativamente mayor que bajo LC. A 5-20 cm de profundidad, las diferencias en COP no fueron claras entre SC aunque, tendió a disminuir con los años bajo agricultura. La fertilización determinó mayor COP a 5-20 y 0-20 cm de profundidad. Las diferencias en la variación entre 1994 y 2003 entre SC fueron significativas para COP y COT. Por otro lado, la variación relativa de COP fue más alta que la de las otras variables. Se concluye que las rotaciones cortas de agricultura-pastura, la SD y la fertilización nitrogenada mejoran el COP y el COT. Para las condiciones de este experimento, COP ha sido un indicador más sensible que COT y sería capaz de detectar los efectos de las prácticas de manejo.In the southeastern Buenos Aires Province (Argentina) unsuitable combination of crop rotation and tillage systems (cropping systems, SC) has reduced soil organic matter content. Our aim was to evaluate the effect of seven SC in a long term experiment (since 1976) started in 1994: permanent pasture (PP), permanent cropping under no tillage (SD) (SD100) and conventional tillage (LC) (LC100), cropping-pasture rotation (50% - 50% of time (3 yr each)) under SD (SD50) and LC (LC50), cropping pasture rotation (75% - 25% of time (6 and 3 yr)) under SD (SD75) and LC (LC75); and two N fertilization rates: 0 and 120 kg N ha-1, on total (COT) and particulate (COP) organic carbon, for 0-20 cm depth in 1994 and for 0-5 cm, 5-20 cm and 0-20 cm depths in 2003. In 1994 COP and COT showed the effect of previous management of different crop rotations under LC, and the shortest the cropping period, the highest COP and COT. In 2003, there were not differences among SC in COT at 5-20 and 0-20 cm depths. At 0-5 cm depth differences were not clear, but PP, LC50 and SD50 (under pasture until sampling) did not differ among them and had COT greater than the other SC. Particulate organic carbon was highest under PP, SD50 and LC50 either at 0-5 and 0-20 cm depths. At 0-5 cm depth there were not differences between SD75 and SD100 nor between LC75 and LC100, although COP under SD was significantly greater than under LC, showing a trend to decrease with cropping years. This difference between tillage systems was not observed at 0-20 cm depth. At 5-20 cm depth, we found unclear differences in COP between SC, although decreasing with cropping years. Total organic carbon was greater at all depths in those plots that had received 120 kg N ha-1, respect to those unfertilized, although not significantly. At 5-20 and 0-20 cm depths, fertilization produced significantly higher COP than without it. Variation between 1994 and 2003 at 0-20 cm depth showed significant differences in COP and COT. There were not differences neither between increases of COP in those SC under pasture in 2003 nor between them and those under SD. On the other hand, relative variation of COP, especially at 0-5 cm depth, was higher than the relative variation of the other variables. It is concluded that short cropping-pasture rotations (50% and 50% of time), SD and N fertilization improve COT and COP and it has been demonstrated the beneficial effect of such practices. For the conditions of this experiment, COP has been a more sensitive indicator than COT, and it would be able to detect management practices effects.

Labile soil organic matter fractions (particulate (COP) organic carbon (CO) and nitrogen (N) released through anaerobic incubation (Nan)) are soil health indicators. However, COP and Nan contents may change in time limiting utility as indicators. The aim of this study was to evaluate seasonal variation of COP and Nan under different managements. Soil samples were taken at 0-5 and 5-20-cm depths at different moments between fall and spring in two years (2007 and 2009) from a complex of Mollisols under contrasting tillage systems (no-tillage (SD) and conventional tillage (LC)) and N fertilization (with and without N). Total CO (COT), COP and Nan contents were determined. In 2009, COP and Nan contents at 0-20 cm (4.8 g kg-1 y 56.2 mg kg-1, respectively) were higher than in 2007 (3.7 g kg-1 y 47.0 mg kg-1, respectively) and, in each year, they were higher under SD and with N, although not always significantly. Besides, in 2009, COT and COP did not change in time, but in 2007 they changed slightly and without clear trends. Nan decreased between July and October sampling times of each year, although significantly only in 2009. In July, Nan at 0-20 cm was 13.5 mg kg-1 higher in 2009 than in 2007, whereas in October the difference was 6.7 mg kg-1. There were inverse relationships between COP and Nan at 0-20 cm and corn response to N, but were significant only for Nan. Such relationships were different between SD and LC and among sampling moments. Given its scarce variation in time, the use of COP as an indicator would be possible regardless of the sampling time. Nan showed more variation in time; the possibility of using Nan as indicator would require more adjustments taking into account the sampling time and/or the previous conditions. [ABSTRACT FROM AUTHOR]

Vertical fluxes of particles have been estimated during the last decade in coastal and oceanic systems off central-southern Chile. Free-drifting, cylindrical sediment traps have been deployed below the mixing layer from coastal areas, while automatic, cone-shaped sediment traps have been anchored in deep oceanic areas. Vertical fluxes toward 2300 m depth off Coquimbo were dominated by calcium carbonate (~70 mg m-2 d-1) instead of particulate organic carbon (POC ~7 mg m-2 d-1), where foraminifers (Neogloboquadrina pachyderma) and faecal pellets of Euphausia mucronata and Oikopleura spp, played important roles as vehicles for carbonate and carbon, respectively. In coastal upwelling systems, (i. e. Concepción), the dominant vertical flux was POC, mainly driven by euphausiids faecal strings and diatoms of the genera Thalassiosira, Chaetoceros and Skeletonema. Bacterial degradation of exported POC towards deeper layer of the ocean seems not to be significantly affected by the oxic versus hypoxic levels of dissolved oxygen characteristics of different water masses.Flujos verticales de partículas han sido estimados durante la última década en sistemas costeros y oceánicos frente a Chile centro-sur. Trampas cilíndricas derivando con la corriente han sido usadas bajo la capa de mezcla de sistemas costeros, mientras que trampas automáticas cónicas han sido ancladas en sistemas oceánicos profundos. Los flujos hacia 2300 m de profundidad frente a Coquimbo estuvieron dominados por carbonado de calcio (~70 mg m-2 d-1) más que carbono orgánico particulado (POC ~7 mg m-2 d-1), donde foraminiferos (Neogloboquadrina pachyderma) y pellet fecales de Euphausia mucronata y Oikopleura spp, juegan un papel muy importante como vehículos de carbonato y carbono, respectivamente. En sistemas de surgencia costera (i.e., Concepción), el flujo vertical dominante fue POC, principalmente gobernado por pellets fecales de eufáusidos y diatomeas de los géneros Thalassiosira, Chaetoceros y Skeletonema. La degradación bacteriana de material orgánico exportado hacia zonas más profundas del océano no aparece significativamente afectada por los niveles característicos de concentración de oxígeno disuelto óxicos versus hipóxicos en las diferentes masas de agua.

O aumento do estoque de matéria orgânica do solo em sistemas conservacionistas de manejo é dependente do tipo de solo e das condições climáticas, e tem reflexos na qualidade física do solo. Neste estudo, avaliou-se um experimento de longa duração (21 anos) quanto ao efeito do sistema plantio direto (PD) sobre os estoques de carbono orgânico total (COT) e particulado (COP, >53mm), bem como a sua relação com a estabilidade de agregados de um Latossolo Bruno, em Guarapuava, PR. O solo em PD apresentou taxa de incremento de 0,15Mg ha-1 ano-1 de COT e 0,06Mg ha-1 ano-1 de COP na camada de 0-20cm, as quais foram calculadas em comparação aos estoques de carbono orgânico do solo em preparo convencional. As baixas taxas de incremento nos estoques de carbono orgânico possivelmente estejam relacionadas à alta estabilidade física da matéria orgânica neste solo argiloso e com mineralogia predominantemente gibsítica. O diâmetro médio geométrico (DMG) dos agregados de solo variou de 1,6 a 3,7mm e foi positiva e linearmente relacionado com os teores de COT e COP, o que reforça a importância da matéria orgânica na qualidade física de Latossolos subtropicais.

Organic matter (MO) has an important influence on soil properties; it is composed of labile (particulate MO, MOP) and stable fractions (humified MO, MOH). Particulate MO is an early indicator of changes due to management practices. On the other hand, potentially mineralizable nitrogen (NPM) is an indicator of the soil capacity to mineralize nitrogen. The objective of this study was to evaluate the effect of four tillage systems (SL): conventional tillage (LC), minimum tillage with disc (LMd), minimum vertical tillage (LMv) and no tillage (SD) on total MO, MOP and MOH contents and on nitrogen mineralization (MN). Soil samples (0-5 and 0-20 cm) were taken froma long-term experiment started in 1990 on an Inceptisol (Udic Ustocrept) in Salta. Average concentrations of the following variables were found under SD and LMv, respectively: MO: 2.93% and 3.16%, MOP 9.62 and 10.98 g kg-1 and MOH 13.62 and 14.63 g kg-1. These values were greater than those found under LMd (2.19%, 7.08 g kg-1 and 9.76 g kg-1) and LC (1.35%, 3.23 g kg-1 and 8.98 g kg-1), for MO, MPO and MOH, respectively, in the soil surface layer. There was a higher quantity of mineralized nitrogen (18 mg N kg soil-1) and potentially mineralizable nitrogen (32 mg N kg soil-1) (CNM and NPM) under LMv compared to the other tillage systems:CNM: LC=6 mg N kg soil-1, LMd and SD=10 mg N kg soil-1; NPM: LC= 16 mg kg soil-1, LMd= 20 mg kg soil-1, SD= 19 mg kg soil-1) in the topsoil. There were stronger dependency relationships between PMN and MOP (R²=0.65) that between the first and MOH (R²=0.32). Organic Matter, MOP, MOH, CNM and NPM were also evaluated as soil quality indicators (ICS). Particulate organic matter and especially the coarse fraction and the CNM were more sensitive indicators for detecting changes caused by different SL. [ABSTRACT FROM AUTHOR]

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O estudo da matéria orgânica do solo e de seus compartimentos visa obter informações a cerca da sua estabilidade e localização na estrutura do solo, bem como sua quantidade e qualidade em sistemas de uso do solo. O objetivo deste trabalho foi avaliar as frações da matéria orgânica em solo sob manejo de plantio direto com gramíneas. O delineamento experimental foi em blocos ao acaso com três repetições e cinco tratamentos (sistemas de cultivos), com medidas repetidas no espaço. Os tratamentos constituíram-se de milho em monocultivo; Brachiaria humidicola; Panicum maximum cv Aruana; milho + Brachiaria humidicola e milho + Panicum maximum cv Aruana. Foram determinados os teores de carbono orgânico total, carbono orgânico particulado e carbono orgânico associado aos minerais do solo nas profundidades de 0-5, 5-10, 10-20 e 20-30 cm. Foram também analisados os acréscimos e reduções dos estoques de carbono nas diferentes frações utilizando-se a área de cerrado como referência. Os resultados demonstraram que os sistemas com consorciação de culturas e forragens ocasionaram efeitos nos diferentes compartimentos da matéria orgânica. Devido ao curto período de condução do plantio direto, as alterações promovidas pelas culturas nas frações da matéria orgânica foram mais expressivas nas camadas superficiais do solo. Sob plantio direto, o milho em monocultivo ou consorciado com Brachiaria humidicola promoveu aumento nos estoques de carbono orgânico total e nas frações COp e COam, tendo o cerrado nativo como referência. Nos demais sistemas, o uso do solo promoveu aumento dos estoques de COT e COam e redução na fração COp.

This paper assesses the long-term effect of no-tillage (NT) on soil organic carbon (OC) content and its distribution among different organic matter fractions in rainfed agrosystems of Aragón (NE Spain). Adjacent fields of NT, conventional tillage (CT) and natural soils (NAT) were compared in three different cereal production areas. In the soil surface, the higher OC content found in the NAT soils was due to the particulate organic matter. In the case of agricultural soils, in general, the fractions responsible for the OC increase under NT were the fine particulate organic matter and the mineral-associated organic matter occluded within stable microaggregates.En este trabajo se evalúa el efecto a largo plazo del no laboreo (NT) en el contenido de carbono orgánico del suelo (OC) y su distribución en diferentes fracciones de materia orgánica en agrosistemas de secano en Aragón (NE España). En tres diferentes zonas cerealistas se compararon campos adyacentes de NT, laboreo tradicional (CT) y suelo natural (NAT). En la superficie del suelo, el mayor contenido en CO encontrado en los suelos NAT se debió a la materia orgánica particulada. En el caso de los suelos agrícolas las fracciones responsables del incremento de OC en NL fueron, en general, la materia orgánica particulada fina y la fracción organo-mineral de los microagregados estables.Este trabalho avalia o efeito a longo prazo do plantio direto (NT) no conteúdo de carbono orgânico no solo (OC) e a sua distribuição em diferentes frações da matéria orgânica em sistemas agrícolas de sequeiro em Aragon (NE Espanha). Campos adjacentes do NT, plantio convencional (CT) e solos naturais (NAT) foram comparados em três diferentes áreas de produção de cereais. Na superfície do solo, o maior teor de OC encontrado nos solos NAT deveu-se à matéria orgânica particulada. No caso dos solos agrícolas, as frações responsáveis pelo aumento de OC em NL foram, em geral, à matéria orgânica particulada fina e a fração organo-mineral de microagregados estáveis.

Soil organic carbon (CO) content determines many soil functions in the agroecosystem, including nitrogen (N) supply to crops. The level and distribution of organic carbon fractions and mineralizable N in the soil depends on management practices. The aim of this work was to analyze total organic carbon content (COT) associated with the mineral (COA) and particulate (COP) fraction and mineralizable N (through N release during anaerobic incubation, NAN) in whole soil and in macro- and microaggregates under different cropping systems (pastures and cropping with conventional tillage (LC) and with no-tillage (SD)) and N fertilization (0 and 120 kg N ha-1). Soil samples were taken from a long-term crop rotation and tillage system trial at Balcarce, Buenos Aires province. Macro- and microaggregates were separated by dry sieving and COT, COA, POC, and NAN content were determined in whole soil and in each aggregate fraction. The soils under pasture showed the highest CO fraction and NAN content both in whole soil and in each of the aggregate fractions. The longer the period under cropping and LC, the lower the variables compared with the SD regime. Although the proportion of macro- and microaggregates did not vary among treatments, a significant correlation was found between COT and POC content in macroaggregates and their stability when soil was less disturbed (pastures and SD). Under LC, aggregate stability was lower and there was no correlation with CO content. Under cropping there was a significant correlation between NAN in whole soil and NAN in the macroaggregates. A higher expression of N mineralization potential can therefore be expected in soils under management techniques that tend to break up macroaggregates or where these are less stable. However, the lack of significant differences in aggregation and in NAN and CO fractions under cropping suggests that careful tilling can help N mineralization largely without affecting its properties and that the inclusion of pastures in the rotation would reverse the effect of cropping. [ABSTRACT FROM AUTHOR]

The soil organic matter (SOM) granulometry fractioning can contribute to the understanding of the SOM dynamics in areas under organic production systems. The objective of this study was to evaluate the granulometry fractions of SOM and total organic carbon in areas with organic management systems and under different soil usages. The selected areas presented the following systems: conventional tillage (CT, corn/beans), no tillage (NT, eggplant/corn), passion fruit and Desmodium sp consortium, fig grove, and agroforest system (AFS). Soil samples were taken in two depths (0-5 and 5-10cm) and two periods of the year (17/11/2005 - summer and 23/06/2006 - winter). The total organic carbon (TOC) was evaluated, and calculated the TOC stocks. The SOM was granulometrically fractioned, obtaining the particulate organic carbon (POC) and organic carbon associated to minerals (OCam). The fig grove and eggplant/corn areas presented the highest TOC and TOC stocks in the summer season. In the winter the crop rotation (NT and CT) systems were more efficient in the stocking of TOC that the other systems. There were observed highest TOC variations in the 5-10cm depth, resulting from the management systems adopted. From the POC values it was possible to identify differences among all systems evaluated, in the summer season and in the 0-5cm depth, standing out the area with no tillage, which showed the highest values, in the two seasons. The POC was more efficient than the TOC, in the summer, to evidence differences among the evaluated soil usage systems, in the 0-5cm depth. The differences observed among the production systems for OCam were attributed to the constant usage of organic manure. [ABSTRACT FROM AUTHOR]

The organic carbon (CO) is a key component that determines many soil properties, and it is composed of labile (particulate CO, COP) and less labile fractions. Particulate CO is an early indicator of changes in CO due to management practices. On the other hand, anaerobic N (Nan) is an indicator of the soil capacity to mineralize N. The objective of this study was to evaluate the effect of no-tillage (SD), conventional tillage (LC) and N fertilization on total CO (COT), COP, total organic N (NOT), particulate organic N (NOP), and of Nan contents, and on their relationship with corn yield. Soil samples (0-5 and 5-20 cm-depths) were taken from two areas of a long term experiment started in 1997 on a Mollisol in Balcarce. There was greater concentration of COP, NOP, COT and NOT under SD compared to LC, especially in the soil surface layer. In general, there were no differences in Nan content between tillage systems. Nitrogen fertilization did not affect either CO and NO fractions or Nan contents. There were no significant relationships between the latter and corn yield or corn response to N fertilization. High CO contents and C returns through crop residues in both tillage systems could have caused the lack of differences expected. The observed results and trends would indicate that significant differences between tillage systems could be manifested in the near future. [ABSTRACT FROM AUTHOR]