Fractal geometry allows describing theoretically structures of diverse nature. From this it obtain the fractal dimension of fragmentation (D), which is related to the partitioning and scaling presented by them, and which has been used in the characterization and study of the size distribution soil particle (DTP). It was proposed to apply the fractal model and investigate the process of micro-structuring in six agricultural soils of the Pampean meadow that have contrasting DTP. The DTP and D were obtained under two pretreatments, one without organic matter (SMO), maximum dispersion, and the other with organic matter (CMO), thus preserving the microstructure. The fractal model applied to the DTP with the SMO pretreatment, in silty loam soils, was able to describe on average 98% of the mass analyzed; in sandy loam soil it adjusted to 50 μm, describing 38% of the mass, while the sandy loam soil did not adjust to the fractal model. With the larger sizes of the sands, they obtained D close to 3, showing Euclidean characteristics, not fractals. The DTP for the CMO pretreatment had similar behavior among the evaluated soils, compared to the SMO pretreatment, the percentages of the fractions corresponding to the clay and silt sizes decreased; and the percentage of the size of the sands increased. These fractions, CMO, were called "apparent clay, silt and sand". The D from the SMO pretreatment were greater than those obtained under the CMO pretreatment. The decrease of the D of the pretreatment CMO, was interpreted as an apparent thickening of the soil product of the microstructure by organic matter (OM). The fit between the contents of apparent clays vs OM was not significant (p = 0.37). The apparent silt fraction vs OM, adjusted significantly to a negative exponential function while the contents of the apparent sands vs OM adjusted significantly with a positive exponential function. The variations of OM significantly modify the microstructure in the silt and sand sizes while the fraction of clay size would be independent of the OM content of the soil, in the analyzed range. In temperate Pampas soils, with a proportion of clay + silt close to 90%, the OM by microstructure reduces the contents of clay and silt size particles, increasing the sand size to values close to 55% and these modifications can be interpreted using the model fractal.

La geometría fractal permite describir teóricamente estructuras de diversa naturaleza. De esta se obtiene, la dimensión fractal de fragmentación (D), la cual, está relacionada con el particionamiento y escalamiento que presentan las mismas, y que ha sido empleada en la caracterización y estudio de distribución de tamaño de partículas del suelo (DTP). Se planteó aplicar el modelo fractal e investigar sobre el proceso de microestructuración en seis suelos agrícolas de la pradera pampeana con DTP contrastantes. Las DTP y las D se obtuvieron bajo dos pretratamientos, uno sin materia orgánica (SMO), máxima dispersión, y otro con materia orgánica (CMO) conservando así la microestructura. El modelo fractal aplicado a la DTP con el pretratamiento SMO, en los suelos franco limosos, alcanzó a describir en promedio el 98% de la masa analizada; en el suelo franco arenoso ajustó hasta los 50 μm, describiendo el 38% de la masa, mientas que el suelo areno franco no ajustó al modelo fractal. Con los tamaños mayores de de las arenas se obtuvieron D próximas a 3, mostrando características euclideanas, no fractales. Las DTP para el pretratamiento CMO tuvieron similar comportamiento entre los suelos evaluados, comparado con el pretratamiento SMO, disminuyeron los porcentajes de las fracciones correspondientes a los tamaños arcilla y limo; y aumentó el porcentaje del tamaño de las arenas. A estas fracciones, CMO, se las denominó "arcilla, limo y arena aparentes". Las D a partir del pretratamiento SMO fueron mayores que las obtenidas bajo el pretratamiento CMO. La disminución de la D del pretratamiento CMO, se interpretó como un engrosamiento aparente del suelo producto de la microestructuración por materia orgánica (MO). El ajuste entre los contenidos de arcillas aparentes vs MO no fue significativo (p=0,37). La fracción limo aparente vs MO, ajustó significativamente a una función exponencial negativa mientras que los contenidos de las arenas aparentes vs MO ajustaron significativamente con una función exponencial positiva. Las variaciones de MO modifican significativamente la microestructuración en los tamaños limo y arena mientras que la fracción de tamaño arcilla sería independiente del contenido de MO del suelo, en el rango analizado. En suelos templados pampeanos, con proporción de arcilla+limo próximas al 90%, la MO por microestructuración, reduce los contenidos de partículas de tamaños arcilla y limo incrementando las de tamaño arenas a valores próximos al 55% y estas modificaciones pueden interpretarse empleando el modelo fractal.

Soil water diffusivity (D) determination is important as this hydraulic property is fundamental in order to characterize unsaturated water and solute transport in soils. Determination of this property is complex, time consuming, and requires quite expensive instruments. The objectives of this work were: i) to propose a simpler and more robust method based on an improvement of Whisler et al. (1968) to determine the soil water diffusivity function and ii) to determine D and sorptivity (S) in a soil under different management systems. Soil A-horizon was sampled under three management systems (T1: Natural grassland, T2: Polyphitic Pasture, and T3: no tillage). The samples were sieved through a 2 mm mesh, and afterwards packed into 70 cm long and 10 cm diameter columns. The columns were analyzed under horizontal infiltration and D was determined as a function of soil water content that varied in function of time for fixed positions along the column, these latter were obtained from low cost soil moisture capacitance sensors. The results showed that the proposed methodology was valid for the studied soils. The soil management system significantly affected D and S values. D values corresponding to T3 were greater compared to T1 and T2 (D values ranged between 0.00033 and 0.0321 cm² s-1) implying that these soils had the ability to transmit water easier under non-saturated conditions than under grazing. In conclusion, the proposed methodology in this work allowed to determine D in a simple and low cost way, and to analyze the influence of soil management systems on this property.

La determinación de la Difusividad (D) del agua en el suelo es importante ya que caracteriza el flujo de agua en condiciones no saturadas. Estimarla es complejo, ya que consume tiempo y generalmente se necesita equipo costoso para hacerlo. Los objetivos de este trabajo fueron: 1- proponer una mejora en el método de Whisler et al. (1968) haciéndolo más simple y robusto, aportando herramientas para probar la validez de la ecuación de Richards en su forma de difusividad y el cumplimiento de los supuestos del modelo y 2- Determinar la D en función del contenido de humedad (θ) y S en un suelo bajo distintas situaciones productivas. Para esto, se tomaron muestras del horizonte superficial de tres lotes contiguos bajo distintos sistemas de manejo (T1: Pastizal natural, T2: Pastura polifítica y T3: Siembra Directa). Las muestras se secaron, tamizaron por 2 mm y se empaquetaron en columnas de PVC de 70 cm de largo y 10 cm de diámetro interno. Las columnas de suelo se sometieron a infiltración horizontal y se determinó la D a distintos valores de θ y la S. Se utilizaron sensores de humedad de capacitancia de bajo costo en puntos fijos de la columna. Los resultados encontrados muestran la validez de la metodología para los suelos estudiados. En cuanto a la influencia del manejo, se encontraron diferencias significativas en los valores de D entre los tratamientos. El T3 presentó mayores valores de D a todas las humedades, y de S, que T1 y T2 (los valores de D estuvieron entre 0,00033 y 0,0321 cm² s-1), lo que indica mayor facilidad para transmitir agua en condiciones no saturadas en el manejo agrícola, lo cual se atribuyó a la influencia negativa del pisoteo animal. La metodología propuesta permitió estimar de manera consistente, simple y de bajo costo la D y estudiar su relación con el manejo del suelo.

The specific surface area of soil samples was estimated by the method of nitrogen adsorption at 78 K, and it was related to the water retention capacity, clay content, cation exchange capacity, and the amount of water retained on the exposed soil surface, in an approximation of superimposed layers. Twenty seven Oxisols were investigated. Soil moisture retention was studied at water potentials -33, -500, -1000 and -1500 kPa. The specific surface area was positively correlated to soil moisture and with clay content. No relationship was found between specific surface area and cation exchange capacity. Between specific surface area and soil organic content only a weak correlation was found. The specific surface area was related with soil moisture content by linear equations obtained by the regression method of data, for each water potential applied. The results showed that the specific surface area of these Oxisols can be reasonable estimated by water retention in a wide range of matrix potentials. Finally, from the obtained data on specific surface area and water retention it was possible to estimate the thickness of the water film covering the entire surface of the soil pores exposed to the air.

Se estimó la superficie específica (SE) de muestras de suelos mediante el método de adsorción de nitrógeno a 78 K, y se la relacionó con la capacidad de retención hídrica (RH), el contenido de arcilla, la capacidad de intercambio catiónico efectiva (CIC), y la cantidad de agua retenida sobre la superficie expuesta del suelo, en una aproximación de capas superpuestas. Se trabajó con veintisiete Oxisoles a potenciales hídricos equivalentes de -33, -500, -1000 y -1500 kPa. Se encontró una correlación positiva significativa entre la SE y RH, así como con el contenido de arcilla. No hubo una relación significativa de la dependencia entre la SE y la CIC. Entre la SE y el contenido de materia orgánica la correlación fue débil. La SE se relacionó con la RH por medio de ecuaciones de regresión lineal para cada potencial aplicado. Los resultados mostraron que la SE de estos Oxisoles puede ser estimada adecuadamente por la retención de agua en el suelo en una amplia gama de potenciales matriciales. Finalmente, de la información de SE y RH para cada suelo se pudo estimar la cantidad de capas de agua que cubren toda la superficie de los poros expuesta al aire.

ABSTRACT The concept of soil physical quality (SPQ) is currently under discussion, and an agreement about which soil physical properties should be included in the SPQ characterization has not been reached. The objectives of this study were to evaluate the ability of SPQ indicators based on static and dynamic soil properties to assess the effects of two loosening treatments (chisel plowing to 0.20 m [ChT] and subsoiling to 0.35 m [DL]) on a soil under NT and to compare the performance of static- and dynamic-based SPQ indicators to define soil proper soil conditions for soybean yield. Soil sampling and field determinations were carried out after crop harvest. Soil water retention curve was determined using a tension table, and field infiltration was measured using a tension disc infiltrometer. Most dynamic SPQ indicators (field saturated hydraulic conductivity, K0, effective macroporosity, εma, total connectivity and macroporosity indexes [CwTP and Cwmac]) were affected by the studied treatments, and were greater for DL compared to NT and ChT (K0 values were 2.17, 2.55, and 4.37 cm h-1 for NT, ChT, and DL, respectively). However, static SPQ indicators (calculated from the water retention curve) were not capable of distinguishing effects among treatments. Crop yield was significantly lower for the DL treatment (NT: 2,400 kg ha-1; ChT: 2,358 kg ha-1; and DL: 2,105 kg ha1), in agreement with significantly higher values of the dynamic SPQ indicators, K0, εma, CwTP, and Cwmac, in this treatment. The results support the idea that SPQ indicators based on static properties are not capable of distinguishing tillage effects and predicting crop yield, whereas dynamic SPQ indicators are useful for distinguishing tillage effects and can explain differences in crop yield when used together with information on weather conditions. However, future studies, monitoring years with different weather conditions, would be useful for increasing knowledge on this topic.

A compactação do solo tem sido reconhecida como um problema grave na agricultura mecanizada, influenciando em várias propriedades e processos do solo. Poucos são os relatos dos efeitos dessa compactação ao longo do tempo; a evolução da compactação do solo tem sido demonstrada por um número limitado de atributos do solo. Os objetivos deste trabalho foram avaliar a persistência dos efeitos da compactação do solo (três tratamentos com tráfego de máquina agrícola, sendo: T0, sem tráfego; T3, com três passadas de trator; e T5, cinco passadas de trator) na configuração do sistema poroso, utilizando determinações estáticas e dinâmicas; e determinar as mudanças na orientação do sistema poroso do solo após a compactação, utilizando os valores de condutividade hidráulica do solo saturado, em amostras coletadas na vertical e horizontal. O tráfego causou alterações em todos os indicadores dinâmicos estudados (condutividade hidráulica do solo saturado, K0; e macro e mesoporosidade efetiva do solo, εma e εme), com valores significativamente baixos de K0, εma e εme no tratamento T5. Já os valores dos indicadores estáticos como a densidade do solo, a porosidade total derivada do solo e a macroporosidade total (θma) não apresentaram variação significativa entre os tratamentos. Esse é um indicativo que o tráfego de máquinas não influenciou na alteração dessas variáveis após dois anos. Já na orientação do sistema poroso do solo, mesmo em T0, ocorreram maiores alterações em K0 medidas nas amostras coletadas na vertical do que os valores medidos na horizontal, sendo mais relacionados à presença de bioporos na vertical e à isotropia de K0 nos tratamentos onde houve tráfego de máquinas. Assim, os resultados evidenciaram que os indicadores dinâmicos são mais sensíveis aos efeitos da compactação e que, futuramente, os indicadores estáticos não serão utilizados como indicadores da compactação do solo, sem a necessidade do complemento de indicadores dinâmicos.

Soil compaction has been recognized as a severe problem in mechanized agriculture and has an influence on many soil properties and processes. Yet, there are few studies on the long-term effects of soil compaction, and the development of soil compaction has been shown through a limited number of soil parameters. The objectives of this study were to evaluate the persistence of soil compaction effects (three traffic treatments: T0, without traffic; T3, three tractor passes; and T5, five tractor passes) on pore system configuration, through static and dynamic determinations; and to determine changes in soil pore orientation due to soil compaction through measurement of hydraulic conductivity of saturated soil in samples taken vertically and horizontally. Traffic led to persistent changes in all the dynamic indicators studied (saturated hydraulic conductivity, K0; effective macro- and mesoporosity, εma and εme), with significantly lower values of K0, εma, and εme in the T5 treatment. The static indicators of bulk density (BD), derived total porosity (TP), and total macroporosity (θma) did not vary significantly among the treatments. This means that machine traffic did not produce persistent changes on these variables after two years. However, the orientation of the soil pore system was modified by traffic. Even in T0, there were greater changes in K0 measured in the samples taken vertically than horizontally, which was more related to the presence of vertical biopores, and to isotropy of K0 in the treatments with machine traffic. Overall, the results showed that dynamic indicators are more sensitive to the effects of compaction and that, in the future, static indicators should not be used as compaction indicators without being complemented by dynamic indicators.

Nos últimos anos, o sistema plantio direto (NT) tem aumentado. Alguns autores indicam que os atributos físicos do solo ficam estáveis após anos cultivando nesse sistema, sendo esse fato discutido por outros autores. O objetivo deste trabalho foi avaliar o efeito do último cultivo após a rotação (1º ano: milho; 2º ano: soja; e 3º ano: trigo/soja) sobre a configuração do sistema poroso do solo e das suas propriedades hidráulicas de diferentes tipos de textura (solo 1: franco; e solo 2: franco-arenoso) da região do pampa argentino, em NT por um longo prazo, para determinar se a estabilidade das propriedades físicas do solo independe do momento da rotação. Adicionalmente, foram comparados os procedimentos para avaliar a macroporosidade, bem como avaliada a eficiência da função de pedotransferência ROSETTA, para estimar os parâmetros do modelo de van Genuchten-Mualen (VGM) desses solos. A configuração do sistema poroso do solo e as propriedades hidráulicas não foram estáveis e se alteraram em razão da rotação da cultura e do último cultivo utilizado na rotação em ambos os solos. Nos dois locais, a condutividade hidráulica do solo saturado (K0), a macroporosidade (εma) e o raio médio ponderado do poro por fluxo (R0ma) aumentaram do 1º para o 2º ano da rotação de culturas e isso se atribuiu ao aumento de macroporos condutores de água pra as raízes de milho. O modelo VGM descreveu adequadamente a curva de retenção de água (WCR) nos dois solos, porém não foi adequada para as curvas de condutividade hidráulica (K) vs tensão (h). A função ROSETTA não foi eficiente para a estimativa dos parâmetros. Em resumo, os valores médios de K0 variaram entre 0,74 e 3,88 cm h-1. Com relação às propriedades físicas do solo no NT, o efeito do cultivo deve ser considerado.

The area under the no-tillage system (NT) has been increasing over the last few years. Some authors indicate that stabilization of soil physical properties is reached after some years under NT while other authors debate this. The objective of this study was to determine the effect of the last crop in the rotation sequence (1st year: maize, 2nd year: soybean, 3rd year: wheat/soybean) on soil pore configuration and hydraulic properties in two different soils (site 1: loam, site 2: sandy loam) from the Argentinean Pampas region under long-term NT treatments in order to determine if stabilization of soil physical properties is reached apart from a specific time in the crop sequence. In addition, we compared two procedures for evaluating water-conducting macroporosities, and evaluated the efficiency of the pedotransfer function ROSETTA in estimating the parameters of the van Genuchten-Mualem (VGM) model in these soils. Soil pore configuration and hydraulic properties were not stable and changed according to the crop sequence and the last crop grown in both sites. For both sites, saturated hydraulic conductivity, K0, water-conducting macroporosity, εma, and flow-weighted mean pore radius, R0ma, increased from the 1st to the 2nd year of the crop sequence, and this was attributed to the creation of water-conducting macropores by the maize roots. The VGM model adequately described the water retention curve (WRC) for these soils, but not the hydraulic conductivity (K) vs tension (h) curve. The ROSETTA function failed in the estimation of these parameters. In summary, mean values of K0 ranged from 0.74 to 3.88 cm h-1. In studies on NT effects on soil physical properties, the crop effect must be considered.

A importância da macroporosidade para o transporte de água no solo faz a sua avaliação de forma quantitativa uma tarefa desafiadora. Os valores da condutividade hidráulica (K) do solo em diferentes potenciais de retenção de água no solo e a quantificação de macroporos condutores de água (θM) em diferentes sistemas de preparo do solo proporcionarão melhor compreensão dos efeitos no arranjo de poros e nas propriedades físico-hídricas do solo. Dessa forma, o objetivo deste estudo foi avaliar os efeitos de um preparo convencional do solo com arado de aivecas (CT), com subsolador (CP) e utilizando um sistema com plantio direto (NT) sobre os atributos θM e K, bem como quantificar a contribuição da macroporosidade para o fluxo total de água em um solo franco. Um infiltrômetro de tensão no solo foi utilizado para emitir duas pressões ascendentes de água (-5 cm e 0 cm) para inferir θM e K, durante o pousio. A macroporosidade foi determinada com base na contribuição do fluxo entre os potenciais de água de 0 e -5 cm (K0 e K5, respectivamente), de acordo com a equação de Hagen-Poiseuille. Os valores da K0 obtidos foram estatisticamente superiores no preparo CT, quando comparados aos valores do NT e do CP. Os valores da K5 não diferiram estatisticamente entre os tipos de preparo. Os valores médios da K variaram entre 0,20 e 3,70 cm/h. A quantificação de macroporos condutores de água (θM) foi significativamente superior para o preparo CT em relação aos preparos CP e NT, seguindo a mesma tendência da K0. Não foram detectadas diferenças significativas dos valores de θM entre os preparos CP e NT. Utilizando o preparo CT, foi possível a formação de macroporos condutores de água com persistência até a pós-colheita; já no preparo CP, os macroporos condutores de água não foram persistentes. Os resultados apresentados sustentam a hipótese de que o sistema de preparo do solo escolhido altera o movimento da água no solo, principalmente, devido à formação de macroporos condutores de água. Estudos futuros sobre o efeito do sistema de preparo relacionado ao movimento da água no solo devem-se concentrar nas condições de formação da macroporosidade do solo.

In view of the importance of the macroporosity for the water transport properties of soils, its quantitative assessment is a challenging task. Measurements of hydraulic conductivity (K) at different soil water tensions and the quantification of water-conducting macropores (θM) of a soil under different tillage systems could help understand the effects on the soil porous system and related hydraulic properties. The purpose of this study was to assess the effects of Conventional Tillage (CT), Chisel Plow (CP) and No Tillage (NT) on θM and on K; and to quantify the contribution of macroporosity to total water flux in a loam soil. A tension disc infiltrometer was used at two soil water pressure heads (-5 cm, and 0) to infer θM and K, during fallow. Macroporosity was determined based on the flow contribution between 0 and -5 cm water potentials (K0, K5, respectively), according to the Hagen-Poiseuille equation. The K0 values were statistically higher for CT than for NT and CP. The K5 values did not differ statistically among treatments. The mean K values varied between 0.20 and 3.70 cm/h. For CT, θM was significantly greater than for CP and NT, following the same trend as K0. No differences in θM were detected between CP and NT. With CT, the formation of water-conducting macropores with persistence until post-harvest was possible, while under CP preparation, the water-conducting macropores were not persistent. These results support the idea that tillage affects the soil water movement mainly by the resulting water-conducting macropores. Future studies on tillage effects on water movement should focus on macroporosity.

Dois cultivares argentinos de trigo (Triticum aestivium L), Buck Cencerro (BC), com germoplasma tradicional e Buck Pucará (BP), com germoplasma mexicano, foram pesquisados para comparar as características anatômicas e fisiológicas da folha bandeira medida no espigamento (estádio E59), na antese (estádio E69) e na fase de grão aquoso completo (estádio E71). Nos dois cultivares, a taxa fotossintética foi semelhante no mesmo estágio fenológico, exceto no E71. As médias no estádio E59 foram superiores às dos estágios E69 e E71 nos dois cultivares (22,70; 18,40 e 10,40 µmol m-2 s-1 para o BP e 23,82; 18,41 e 8,28 µmol m-2 s-1 para o BC, respectivamente). Nos três estádios, as taxas de transpiração foram maiores no BP (5,0; 5,6 e 4,89 mmol m-2 s-1) comparado ao BC (3,3; 4,4 e 2,57 mmol m-2 s-1). Consequentemente, a eficiência de uso instantâneo de água foi maior no BC, quando comparado com o BP. Não foram observadas diferenças de área foliar específica para cultivares e estádios fenológicos (área do mesófilo por unidade de massa), determinada por adsorção física de nitrogênio a baixa temperatura (78° K), registrando-se média geral de 8,9 m² g-1. Esse valor foi semelhante a outros reportados em trabalhos prévios com T. aestivum L. e maiores que os determinados para Ligustrum lucidum Aiton, pela mesma técnica. As diferenças podem ser atribuídas à rugosidade da parede celular e as próprias dimensões da célula. Não houve correlação positiva entre área específica e taxa fotossintética para cultivares ou estádios fenológicos.

Two Argentine field grown wheat cultivars (Triticum aestivum L.), Buck Cencerro (BC) with traditional germoplasm, and Buck Pucará (BP) with Mexican germoplasm, have been investigated in order to compare anatomical and physiological characteristics of the flag leaf measured in heading (stage E59), anthesis (stage E69) and kernel water ripe (stage 71). In both cultivars, photosynthetic rate was not different for the same phenological stage, except for E71. Averages in stage E59 were higher than stages E69 and E71 for both cultivars (22.70, 18.40 and 10.40 µmol m-2 s-1 for BP and 23.82, 18.41 and 8.28 µmol m-2 s-1 for BC, respectively). Transpiration rates were higher in BP (5.0, 5.6 and 4.89 mmol m-2 s-1) than BC (3.3, 4.4 and 2.57 mmol m-2 s-1) for stages E59, E69 and E71, respectively. Consequently, instantaneous water use efficiencies were higher in BC than in BP. No difference between cultivars and phenological stages was observed in specific surface area (mesophyll area per unit mass) determined by physical adsorption of nitrogen at low temperature (78° K); the mean was 8.9 m² g-1. It was similar as values found in previous works, in others T. aestivum L. and greater than the values found for Ligustrum lucidum Aiton, by the same technique. Differences could be attributed to the roughness of the cell wall and the dimensions of the cell itself. No positive correlation between specific surface and photosynthetic rate was observed neither for cultivars nor for phenological stages.