Dorota Dec

THE ROLE OF SOIL STRUCTURE ON THE PORE FUNCTIONALITY OF AN ULTISOL

A Typic Hapludult was used to evaluate the effect of soil structure and different bulk densities (reached after the destruction of macro aggregates) on functional characteristics of the pore system. The water retention curve, pore-size distribution, shrinkage curve and index were determined in disturbed and structured samples. To evaluate the effect of soil structure on the continuity of the pore system the air permeability at different matrix potentials was measured. From the relationship between the air permeability and air-filled porosity, pore continuity indexes were calculated. The destruction of the soil structure affects the function of its pores. The amount of air-filled pores increased with the reduction of the bulk density, however, the stability and continuity of these pores are low, which affects their functionality. Therefore, the formation of a stable and continuous pore system allows the soil to conduct air, even though they have a restrictive amount of air-filled pores. On the other hand, the soil structure plays a key role in pore stability during drying and, consequently, on the equilibrium between phases. Finally, the highest bulk density (1.1 Mg m-3) does not reach critical values (compaction). However, depending on the bulk density of the soil, it is possible to reach restrictive values of air capacity which affects the air transport in the soil, especially if the porous media is not continuous.

Temporal and spatial variability of structure dependent properties of a volcanic ash soil under pasture in southern Chile

Prairies are a main source for livestock feeding in southern Chile. The aim of this research was to define how grazing events and natural wetting and drying cycles (WD) affect the spatial and temporal variability of the soil?s structural properties. The investigation was conducted in a Duric Hapludand, Valdivia Series. Penetration resistance (PR) and volumetric water content (WC), measured in situ, were used to prepare maps which show i) temporal (1383 to 3047 kPa for 46 to 16% WC) and spatial changes, and ii) grazing events as an important factor influencing spatial changes in PR (differences of 3421 kPa between max and min values). Grazing and WD cycles induced changes in the soil?s mechanical stability and pore functions, which indicate that structure-dependent properties are dynamic. During the study, variations between 0.3 and 0.9 log im2 were detected for air permeability (ka), whereas air capacity (ACp) ranged between 5 and 18%. Soil mechanical strength also varied over time and showed changes in PR. The same instrument, however, cannot be used to identify changes in soil pore functions. Generally, after grazing events, soil deformation induced a reduction of air capacity and permeability; however, after WD cycles, soil pores were able to recover their functional integrity.

EFFECT OF BULK DENSITY ON HYDRAULIC PROPERTIES OF HOMOGENIZED AND STRUCTURED SOILS

In order to determine the effect of bulk density and soil structure on their hydraulic behaviour, undisturbed samples were collected and disturbed samples were prepared from a Luvisol. The experimental field, located in Harste/Goettingen, Germany, was cultivated with sugar beet (Beta vulgaris). The water retention curve (WRC) and saturated hydraulic conductivity (Ks) were measured on undisturbed samples and homogenized samples prepared at different bulk densities (1.2 -1.4 and 1.6 Mg m-3). To determine the effect of soil shrinkage on the unsaturated hydraulic conductivity (k/ψ), the vertical deformation of the repacked samples was measured and relative water content differences (dθ)were determined. The hydraulic properties of soils with identical texture depend on bulk density (dB) and structure. The increasing bulk density not only induces changes in the pore-size distribution but also affects the ability of soil to shrink and to conduct water under unsaturated conditions. Greater shrinkage was observed for samples with lower dB as a consequence of reduction of coarse pores. The water content differences increase with decreasing bulk density, inducing an increasing error in the estimation of k/ ψ.

EFECTO DEL CAMBIO DE USO EN LA ESTABILIDAD DE LA ESTRUCTURA Y LA FUNCIÓN DE LOS POROS DE UN ANDISOL (TYPIC HAPLUDAND) DEL SUR DE CHILE

Los suelos volcanicos del sur de Chile constituyen cerca del 60% del suelo arable del pais. Estos suelos se encuentran bajo un amplio rango de usos desde sistemas pristinos hasta otros con un uso intensivo. El objetivo de este trabajo fue determinar el efecto del cambio de uso de suelo sobre: i) la estabilidad del suelo frente a presiones externas e internas; ii) la conductividad hidraulica y iii) su resiliencia funcional. Muestras disturbadas y no disturbadas de suelo fueron recolectadas a 5, 20, 40 cm de profundidad en un suelo Andisol (Typic Hapludand) bajo un renoval de bosque nativo (NF), una pradera de 50 anos (P50) y otra de 1 ano de uso (Pl). Se determino la curva de retencion de agua, contraccion y consolidacion, la conductividad hidraulica saturada (Ks), permeabilidad de aire (Ka), contenidos de carbono organico (CO), textura y alofan. Se estimo la conductividad hidraulica no saturada (Ku) de acuerdo al modelo propuesto por van Genuchten (1980). Se definieron indices de deformacion de suelo como consecuencia de estreses mecanicos (COELm) e hidraulicos (COELh). El suelo estudiado esta sujeto a constantes cambios en su estructura como consecuencia de estreses mecanicos e hidraulicos afectando la distribucion de los poros y su funcionalidad. La magnitud de estos cambios disminuye con el incremento de la intensidad de uso del suelo. La gran capacidad de contraccion del suelo puede traer consecuencias en su comportamiento hidraulico dependiendo de la intensidad del secado a traves de la formacion de grietas y vias de flujo de preferencial. Finalmente, los poros del suelo son capaces de recuperar su integridad funcional despues de una compactacion, lo que esta estrechamente relacionado con los contenidos de materia organica.

LA PERMEABILIDAD DEL AIRE Y CONDUCTIVIDAD HIDRÁULICA SATURADA COMO HERRAMIENTA PARA LA CARACTERIZACIÓN FUNCIONAL DE LOS POROS DEL SUELO

Con el objetivo de describir los aspectos funcionales de los poros de suelos labrados, se recolectaron muestras no disturbadas en dos profundidades y orientaciones (vertical y horizontal) en suelos estructurados del Norte de Alemania. Se determino la curva de retencion de agua, la permeabilidad de aire (ka) y la conductividad hidraulica en fase saturada (kf). Se calculo la distribucion de poros por tamano, la porosidad de aire e indices de continuidad de poros. El manejo agricola afecta al suelo cuantitativa y cualitativamente. La formacion de un pie de arado implica no tan solo una reduccion del volumen de poros sino que tambien causa una dependencia espacial de las propiedades hidraulicas del suelo a traves de la formacion de una estructura laminar. Con el objeto de establecer dichos cambios cualitativos, mediciones como ka y kf son una buena herramienta para describir la calidad fisica del suelo

EFFECT OF SOIL MANAGEMENT ON THEIR THERMAL PROPERTIES

In order to determine the effect of soil management on its thermal properties, undisturbed soil samples were taken from two tillage treatments (conventional and conservation treatment) at two depths (0-30cm and 30-60cm) of a Stagnic Luvisol (silt loam) before and after directly wheeling. The experimental field, located in Harste/Goettingen, Germany, was cultivated with sugar beet (Beta vulgaris). To calculate thermal properties of the soil, the volumetric water content (TDR needles) and temperature (pT 100 thermistors) during the simulation of the daily fluctuation of temperature were registered in laboratory and then the thermal conductivity, volumetric heat capacity and heat diffusivity were calculated following the damping depth method and the statistical-physical model. The results showed that different tillage systems as well as compaction influenced soil thermal properties. Conservational tillage treatment with more stable and better developed soil structure at a depth of 0-30cm (which represents ploughing depth and decides differences between soil management) presented higher water content as the main factor deciding soil thermal properties. According to this, values of thermal conductivity and volumetric heat capacity under this treatment were greater than under conventional. Thermal diffusivity, however, was lower. From the latter we can conclude that under conservation tillage treatment the soil can store more heat, but at the same time and as a result of the lower thermal diffusivity, the atmospheric variations do not affect the soil thermal regime strongly.

Spatial variability of the hydraulic properties of a drip irrigated andisol under blueberries

The objective of the present investigation was to identify the spatial variability of hydraulic properties of a volcanic ash soil under irrigated Blueberry crops, in order to improve the irrigation efficiency in a very sensitive crop by excess or lack of water. Undisturbed samples (230 cm 3 ) were collected in area of 945 m 2 (grid: 72 points separated by 3.2 and 6.4 m) between 1 and 7 cm depth in an Acrudoxic Fulvudands to determine the bulk density (Bd), total porosity (TP), the volume of water-filled pore space (ea (6kPa) ), plant available water (PAW), permanent wilting point (PWP) and saturated hydraulic conductivity (Ks). Along with sampling, volumetric water content (θ (Field) ) was measured using a TDR (grid: 120 points spaced by 1.4 and 3.2 m). From all results contour maps were developed, using geostatistical tools. The coefficient of variation of (θ (Field) ), Ks, (ea (6kPa) ) and PAW showed a moderate variability (15 % - 35 %). The dependence degree (DD) was considered as weak for θ (Field) , moderate for θ (6kPa) , ea (6kPa) , PAW and high for Bd, TP, Ks and θ (0.1kPa) . The properties with largest DD were soil structure-dependent, whereas, the lowest values were observed for those related to soil texture (in this case θ (Field) , which were close to the PMP). The spatial variability was related to the high water storage capacity and the ability of the soil to conduct water with different intensities, what is related to the amount of water-filled macropores.

Water and temperature dynamics of Aquands under different uses in southern Chile

Aquands are soils derived from holocenic volcanic ashes located in southern Chile. Due to the presence of very high levels of organic matter (30 %), these soils present a high total porosity (80 %) but at the same time, a limited water storage capacity due to their shallow soil depths. The aim of this work was to analyze the influence of land use change of a Duric Histic Placaquand (Nadi) soil on soil physical properties and their consequences on water and temperature dynamics. The volumetric water content (qField) and soil temperature (T) were registered at different depths in a Nadi soil under a secondary native forest (sNF) and naturalized grassland (NG). Undisturbed soil samples were collected to analyze the water retention curve, saturated (Ks) and unsaturated (Ku) hydraulic conductivity and water repellency. The dynamics of rainfall and water table depth (WT) were registered using a rain gauge and groundwater wells. The land use change of a Nadi soil from sNF to NG induced soil structural changes in the first 15 cm of soil reducing the amount of macropores under NG and affecting the hydraulic conductivity function as well as qField and T dynamics, i.e. while the WT in winter reached the soil surface in the NG, under sNF the air-filled pores were still present. Similarly, the T gradients increased as qField decreased, being more intensive under NG. A nonhomogeneous soil wetting and water infiltration was assessed, which can be related to an increased spatial water repellency, soil hydraulic properties and rainfalls.