[Truncated abstract] Root-induced changes to soil hydraulic properties (SHP) are an essential component in understanding the hydrology of an ecosystem, and the resilience of these to climate change. However, at present our capacity to predict how roots will modify SHP and the consequences of this is limited because our knowledge of the processes and effects are highly fragmented. Also, current models used to investigate the relationship between plants and root-induced changes to SHP are based on empirical relationships which have limited applicability to the various and often contrasting ecosystems that occur. This thesis focuses specifically on the quantifying the processes by which roots modify SHP and developing models that can predict changes to these and the water balance. Both increase and decreases in saturated hydraulic conductivity have been attributed to the presence of roots. In general, decreases occur when the root system is relatively young, and increases occur when the roots senesce and begin to decay, creating voids for water flow. The evidence available suggests that the change in pore geometry created by roots is the dominant process by which roots modify SHP because they are more permanent and of a greater magnitude than changes to fluid properties or soil structure. We first quantified the effects of wheat roots on SHP of a coarse sand with a laboratory experiment where we measured changes in both SHP and the root system at 3, 5, 7 and 9 weeks after sowing (weeks). ... The main message that can be drawn from this thesis is that root-induced changes to SHP are dynamic, and dependent upon the combination of soil texture, connectivity of root-modified pores and the ratio of root radius to pore radius. Consequently, root-induced changes to the water balance have the same dependencies. The work in this thesis provides a significant first step towards improving our capacity to predict how roots modify soil hydraulic properties. By defining the range for the parameters used to predict how the soil is modified by roots, we are able to make quantitative assessments of how a property such as hydraulic conductivity will change for a realistic circumstance. Also , for the first time we have measured changes in soil hydraulic properties and roots and have been able to establish why a rapid change from a root-induced decrease to increase in Ks occurred. The link between physiological stage of the root system, and the changes that are likely to occur has implications for understanding how roots modify SHP: it may provide an effective tool for predicting when the switch from a decrease to increase occurs. Further work is required to test the validity of the assumptions we have made in our models that predict changes to SHP. While we have endeavoured to define the parameter space for those parameters that we have introduced, there is still some uncertainty about the connectivity of root-modified pores. Also, the parameterisation of the soil domain with roots is based upon work that measures 'fine' roots only which may not provide a true representation of the effect trees and perennial shrubs have on SHP. It is inevitable that root-induced changes to SHP will affect the fate of solutes in the soil, and temporal dynamics of root-induced changes to these may be particularly important for the timing of nutrient and pesticide leaching.

Mass and energy flow processes in soil are strongly dependent on the state of the soil structure and on pore space geometry. To correctly describe these transport processes, an adequate pore space characterization is required. In this context, the use of computerized microtomography allows the visualization of the soil structures and processes that occur at large scales may be very useful, besides being a fast and non-destructive technique. Soil hydraulic properties, which are essential in the quantification of water balance components in hydrological models of the unsaturated zone, can be measured directly with field or laboratory methods. Simultaneous determination of these properties can be done by the Wind-Schindler evaporation method, but determining only the retention function is a more common practice. The relation between soil water retention and hydraulic conductivity can then be predicted using theories like those developed by Childs and Collis-George, Burdine and Mualem. These models treat pore-space tortuosity and connectivity as an empirical parameter, and its value remains usually undetermined, the use of a standard value being more common. Based on this contextualization, the objectives of this thesis are: (i) to evaluate the correlation between soil hydraulic properties measured in the laboratory, and parameters that quantify soil pore space from 3D images obtained by X-ray microtomography; and (ii) to functionally analyze soil hydraulic property parameterization in the prediction of soil water balance components by an agrohydrological model. To verify the relationship between soil hydraulic properties and soil image parameters, a stepwise multiple regression analysis was performed between the pore space parameters from images and empirical parameters of the semi-deterministic model, obtained with evaporation experiments together with an inverse solution method. Functional evaluation of soil hydraulic parameters was performed by a sensitivity analysis of the outputs of an agro-hydrological model to several ways of obtaining the tortuosity/connectivity parameter: applying the commonly used standard value, or determining its value in evaporation experiments in the laboratory with wet-range tensiometers, dry-range tensiometers, or both wet- and dry-range tensiometers. Simulations with the agro-hydrological model were performed for some years with distinct rainfall characteristics. The soil retention curve obtained using soil images had a good agreement to the retention curve obtained by the evaporation experiment, although the spatial resolution of the microtomograph allowed to only quantify macropores, consequently, to determine the hydraulic properties in a small range close to saturation. Soil hydraulic parameterization using a wide range of pressure heads is recommended for a better representation of vadose zone processes and soil-water-plant relations / Os processos de fluxo de massa e energia no solo dependem fortemente do estado da estrutura do solo e da geometria do espaço dos poros. Para descrever corretamente esses processos de transporte, é necessária uma caracterização adequada do espaço poroso. Neste contexto, o uso da microtomografia computadorizada permite a visualização das estruturas do solo e os processos que ocorrem em grandes escalas podem ser muito úteis, além de ser uma técnica rápida e não destrutiva. As propriedades hidráulicas do solo, que são essenciais na quantificação dos componentes do balanço hídrico em modelos hidrológicos da zona não saturada, podem ser medidas diretamente com métodos de campo ou laboratório. A determinação simultânea dessas propriedades pode ser feita pelo método de evaporação Wind-Schindler, mas a determinação apenas da função de retenção é uma prática mais comum. A relação entre a retenção de água do solo e a condutividade hidráulica pode então ser predita por teorias como as desenvolvidas por Childs e Collis-George, Burdine e Mualem. Esses modelos tratam a tortuosidade e conectividade do espaço poroso como um parâmetro empírico, e seu valor permanece geralmente indeterminado, sendo o uso de um valor padrão mais comum. Com base nessa contextualização, os objetivos desta tese são: (i) avaliação da correlação entre propriedades hidráulicas do solo, medidas em laboratório e parâmetros que quantificam o espaço de poros do solo a partir de imagens 3D obtidas por microtomografia de raios X; (ii) a análise funcional da parametrização das propriedades hidráulicas do solo na predição dos componentes do balanço hídrico do solo por um modelo agro-hidrológico. Para a verificação da relação entre as propriedades hidráulicas do solo e os parâmetros da imagem do solo, foi realizada uma análise de regressão múltipla entre os parâmetros do espaço poroso por imagens e parâmetros empíricos do modelo semi-determinística, obtidos com experimentos de evaporação juntamente com método de solução inversa. A avaliação funcional das parametrizações hidráulicas do solo foi feita pela análise de a sensibilidade das saídas de um modelo agro-hidrológico a várias maneiras de obter o parâmetro de tortuosidade/conectividade: aplicando um valor fixo comumente utilizado ou determinando seu valor em experimentos de evaporação no laboratório com tensiômetros na faixa úmida, tensiômetros na faixa seca, ou com tensiômetros nas faixas seca e úmida. As simulações com o modelo agro-hidrológico foram realizadas por vários anos com disponibilidade de água distinta. A curva de retenção de solo obtida através de imagens do solo está em concordância com a curva de retenção obtida pelo experimento de evaporação, embora a limitação da resolução espacial da microtomografia, permitiu apenas quantificar macroporos, consequentemente, a determinação das propriedades hidráulicas em uma pequena faixa próxima à saturação. A parametrização hidráulica do solo usando uma faixa mais ampla de tensões é recomendada para melhor representar os processos na zona não-saturada e das relações solo-água-planta

Although, the potential of management induced changes of soil organic matter, soil hydraulic properties (SHPs) and soil physical quality has been studied particularly in relation to tillage, few studies have evaluated combined effect of tillage, crop residue retention and cropping sequence, which are essential components of conservation agriculture (CA), on stratification and storage of soil organic matter, its effect on near-saturated soil hydraulic properties and soil physical quality in intensive cereal based irrigated cropping systems. Hence, the present study critically analyses the effects of CA on organic matter and hydro-physical properties of soil in a long-term CA field trial in NWIGP, India, which is one of the most fragile agro-ecosystems in the world. The objectives were (I) to investigate the stratification of soil organic carbon (SOC), total nitrogen (TN), C/N ratio and evaluate SR as an indicator of storage of SOC and TN and soil quality for different CA practices, (II) to assess the long-term effect of CA practices and short-term effect of crops on near-saturated soil hydraulic conductivity and water transmission properties, and (III) to assess the effect of CA practices on soil physical quality using capacitive and dynamic indicators. There were four treatments: (1) conventionally tilled rice-wheat cropping system (CT-RW), (2) reduced till CA-based rice-wheat-mungbean system (RT-RWMB), (3) no-till CA-based rice-wheat-mungbean system (NT-RWMB), and (4) no-till CA-based maize-wheat-mungbean system (NT-MWMB). To achieve these objectives, soil bulk density, SOC and TN were measured in an increment of 5 cm up to 30 cm soil depth. Furthermore, the effects of CA were also evaluated in terms of soil hydro-physical properties. Soil physical properties such as bulk density and soil aggregate distribution were evaluated in two cropping seasons along with near saturated hydraulic properties. Steady state infiltration rates were obtained at four pressure heads by hood infiltrometer consecutively over two cropping seasons, i.e. during harvest season of rice/maize (October 2017) and maximum crop growth stage of wheat (February 2018). Data were analysed in terms of soil hydraulic conductivity, k(h), flow weighted mean pore radius (r0), hydraulically active porosity (ε) and threshold pore radius (rbp), a new pore measure indicative of macropore stability derived by substituting soil’s bubble pressure in the capillary equation. Finally, the effects of CA on soil physical quality in terms of both capacitive and dynamic indicators, derived from soil moisture retention curve and field measured hydraulic conductivity, respectively, were assessed and related with crop yield to infer which indicator better represented the soil physical quality and its effect on crop yield under irrigated intensive cereal based cropping systems. Results showed that CA had profound impacts on distribution of SOC and TN in the soil profile. Significantly higher proportion of both SOC and TN were observed in the top soil in the CA-based treatments as compared with conventional intensive tillage-based treatment. The mean stratification ratio of both SOC and TN were found > 2 in CA-based treatments whereas the same was < 2 in intensive tillage-based treatment. Storage of SOC and TN in the 0-30 cm were found higher in CA-based treatments as compared with the intensive tillage-based treatment. These results on vertical distribution and storage of SOC and TN indicated a relatively better soil carbon sequestration and soil quality in CA-based treatment. The higher concentrations and storage of soil organic matter in CA-based treatments were, however, not translated into significantly (p < 0.05) lower bulk density due to probable compaction effect of no-tillage and harvest machinery and hydraulic pressure exerted by the flooded irrigation water. However, the increased soil organic matter in the top soil in CA-based treatments improved the soil aggregation significantly which helped in enhancing soil structural quality. Improvement in soil structure was reflected in relatively higher near saturated hydraulic conductivity in CA-based treatments. Irrespective of crop seasons, higher k(h) was observed under CA due to formation of macropores with better continuity, greater size and numbers as compared with conventional intensive tillage treatment. Moreover, higher r0 values were observed for a given k(h) for CA treatments suggesting that interaggregate pores are the dominant pathways of infiltration in CA. A relatively smaller temporal variation of rbp was indicative of a more stable macropore system established by rice-based CA as compared with maize-based CA. CA also enhanced hydraulically active macropores as compared with intensive tillage based conventional agriculture. Results also indicated that crops play an important role in relative distribution of the hydraulically active macropores in the root zone. The impact of CA on soil organic matter stratification and soil hydraulic properties were found to be expressed in terms of changes in soil physical quality. Soil moisture retention curves and pore size distributions under different treatments suggested higher soil water storage in structural pores in CA as compared with intensive tillage-based conventional agriculture. The impact of CA on soil physical quality and consequent effect on crop yield was found to be more expressed through dynamic indicators such as hydraulically active porosity rather than capacitive indicators derived from soil moisture retention curve. Overall, this study reveals that conservation agriculture has great potentials to reverse the intensive tillage induced degradation of soil resources in Indo-Gangetic Plains of India by improving the soil hydro-physical properties and soil physical quality.:Table of Contents Declaration i Declaration of Conformity ii Acknowledgements iii Table of Contents v List of Figures vii List of Tables xi List of Symbols, Abbreviations and Acronyms xiv Abstract xvii 1 Introduction and Background 1 1.1 General Overview 1 1.2 Statement of the Research Problem 5 1.3 Objectives 6 1.4 Research Flow and Chapter Description 7 2 Materials and Methods 9 2.1 Study Area Description 9 2.1.1 Study site 9 2.1.2 Climate 9 2.1.3 Soil 10 2.1.4 Treatments 10 2.1.5 Field Campaigns and Measurement/Analysis 14 2.2 Methods and Theoretical Considerations 14 2.2.1 Soil Sampling and Analysis 14 2.2.1.1 Calculation of Stratification Ratio 15 2.2.1.2 Calculation of SOC and TN Storage 15 2.2.1.3 Aggregate Size Distribution 16 2.2.2 Infiltration Measurements 16 2.2.3 Soil Moisture Retention Experiments 17 2.2.4 Derivation of Hydraulic Properties from Steady State Infiltration Rates 18 2.2.4.1 Near-Saturated Hydraulic Conductivity 18 2.2.4.2 Flow Weighted Mean Pore Radius 20 2.2.4.3 Equivalent Threshold pore Radius 21 2.2.4.4 Hydraulically Active Porosity 21 2.2.5 Determiation of Soil Moisture Charachtristics and Pore Size Distribution 22 2.2.6 Derivation of Soil Physical Quality Indicators 23 2.3 Statistics 25 3 Results and Discussion 26 3.1 Stratification and Storage of Soil Organic Matter 26 3.1.1 Bulk Density 26 3.1.2 Concenrations of SOC 27 3.1.3 Concentrations of TN 28 3.1.4 C/N Ratio 29 3.1.5 Stratification Ratio of SOC, TN and C/N Ratio 30 3.1.6 Storage of SOC and TN 33 3.1.7 Discussion 34 3.1.8 Summary of Results 39 3.2 Soil Hydro-Physical Properties 40 3.2.1 Soil Physical Properties 40 3.2.2 Near-Saturated Hydraulic Conductivity 43 3.2.3 Soil Pore Characteristics-Conductivity Relationship 47 3.2.4 Hydrailically active Porosity 51 3.2.5 Summary of Results 54 3.3 Soil Physical Quality (SPQ) 56 3.3.1 Soil Moisture Retention Curve (SMRC) 56 3.3.2 Soil Pore Size Distribution (SPSD) 58 3.3.3 Capacitive Indicators 59 3.3.4 Dynamic Indicators 60 3.3.5 Relationship between capacitive indicators of SPQ with dynamic indicators of SPQ and long-term crop yield 60 3.3.6 Relationship between dynamic indicator of SPQ (hydraulically active porosity) and Long-term Crop Yield 62 3.3.7 Summary of Results 64 4 Synthesis and Conclusions 65 5 Implications and Outlook 69 References 71

Die Wurzelwasseraufnahme aus dem Boden wird durch die Rhizosphäre beeinflusst. Die Rhizosphäre ist eine dünne Bodenschicht, die sich um Wurzeln herum bildet. Die Rhizosphäre wird durch Mucilage beeinflusst. Mucilage ist ein polymeres Gel, was von Wurzeln abgesondert wird und vor allem die hydraulischen Eigenschaften der Rhizosphäre verändert. Wenn es im Kontakt mit Wasser ist, kann Mucilage große Mengen an Wasser aufnehmen, aber wenn es trocken ist, wird seine Oberfläche hydrophob. Hier konzentrieren wir uns auf den Effekt von Mucilage auf die hydraulischen Eigenschaften des Bodens. Zunächst präsentieren wir experimentelle und numerische Studien, die die hydraulischen Prozesse in der Rhizosphäre nach der Bewässerung von trockenem Boden beschreiben. Bei Mucilagekonzentrationen, die niedriger als ein gewisser Schwellwert waren, konnte Wasser durch die Rhizosphärenschicht fließen, über dieser Konzentration wurde die Schicht wasserundurchlässig während der ersten Minuten bis zu Stunden nach Bewässerung. Wir präsentieren eine analytische Abschätzung der Mucilagekonzentration an der Perkolationsschwelle als Funktion von mittlerer Teilchengröße und Bodenwasserpotential nach Bewässerung. Die Abschätzung wurde an Hand von Experimenten des kapillaren Aufstiegs in Bodensäulen validiert. Wir entwickelten ein effektives Model um zu beschreiben, wir Mucilage die hydraulischen Funktionen des Bodens verändert: (a) Quell- und Trocknungsprozesse von Mucilage resultieren in Nicht-Gleichgewichtsdynamiken zwischen Wassergehalt und Wasserpotential, (b) die Präsenz von Mucilage im Boden reduziert das Wasserpotential bei einem gegebenen Wassergehalt und (c) Mucilage ist viskos und reduziert dadurch die hydraulische Leitfähigkeit des Bodens bei einem gegebenen Wassergehalt. In Experimenten mit Boden-Mucilage-Mischungen testeten wir das Model und wandten es an, um Beobachtungen von früheren Experimenten mit echten Pflanzen zu simulieren, die veränderte hydraulische Dynamiken in der Rhizophäre zeigen. Im Anhang dieser Arbeit sind zwei Studien zur Wärmeausbreitung von Erdkabeln. Hier können hydraulische Dynamiken autreten, die dem radialen Wasserfluss zu einer einzelnen Wurzel ähneln.

Soil hydraulic properties, such as saturated hydraulic conductivity (Ks), have high spatial variation, but little is known about how to vary a few measurements of Ks over an area to model hydrology in a watershed with complex topography and multiple land uses. Variations in soil structure, macropores (especially in soil that shrink and swell), land use, and soil development can cause large variations in Ks within one soil type. Characterizing the impacts of soil properties that might vary systematically with land use and terrain attributes on Ks rates would provide insight on how management and human activity affect local and regional hydrology. The overall objective of this research was to develop a strategy for using published infiltration and Ks measurements by the Natural Resources Conservation Service for watershed hydrology applications in a Vertisol, and to extend this knowledge toward developing recommendations for future infiltration measurements. To achieve this goal, soil infiltration measurements were collected across three catenas of Houston Black and Heiden clays (fine, smectitic, thermic Udic Haplusterts) under three land uses (improved pasture, native prairie, and conventional tillage row crop). Measurement locations were selected to account for variation in terrain attributes. Overall, Ks values were not significantly different across different landscape positions; however, in fields under similar land uses, Ks values were found to be lower in the footslope positions and higher in the backslope positions. The pedotransfer function, ROSETTA, provided estimates of 64 percent of the overall variability in Ks while also providing accurate estimates of the mean of Ks when particle size distribution and bulk density are used as inputs in the model. Through the use of multiple regression analysis, soil antecedent water content, bulk density, clay content, and soil organic carbon along with two indicator variables for the catenas were highly correlated (r2 = 0.59) with Ks. The indicator variables explained 17 percent of the variation in Ks that could not be explained by measured soil properties. It is recommended that when NRCS measures Ks on benchmark soils, especially high clay soils, that they collect particle size distribution, bulk density, organic carbon, and antecedent water content data.

Die Berücksichtigung der flächenhaften bodenhydraulischen Variabilität gilt bei der Modellierung von Wasser- und Stofftransportprozessen als problematisch. Dies liegt vorrangig an ihrer Erfassung, die kosten- und zeitintensiv ist. Die vorliegende Arbeit untersucht verschiedene Messstrategien, die zur Abbildung der flächenhaften Bodenhydraulik mit wenigen, einfach zu bestimmenden und physikalisch begründeten Bodenparametern führen. Die Vorgehensweise erfolgt mit der Anwendung eines Ähnlichkeitskonzeptes, das die Böden in bodenhydraulisch ähnliche Klassen unterteilt. Innerhalb einer Klasse kann die Variabilität der Retentions- und hydraulischen Leitfähigkeitcharakteristik auf einen freien Parameter (Skalierungsparameter) reduziert werden. Die Analyse der Zusammenhänge zwischen Boden- und Skalierungsparametern führt letztendlich zu den geeigneten Parametern die eine flächenhafte Abbildung möglich machen. Diese Untersuchungen bilden die Grundlage für die weitere Entwicklung eines stochastischen Modellansatzes, der die Variabilität der Bodenhydraulik bei der Modellierung des Bodenwassertransportes im Feldmaßstab berücksichtigen kann. An Hand von drei Datensätzen unterschiedlicher Skalenausbreitung konnte dieses Konzept angewendet werden. Die Ergebnisse zeigen, dass die Beschreibung der hydraulischen Variabilität nur für die vertikale (Profil) nicht aber für die flächenhafte Ausbreitung mit einfachen Bodenparametern möglich ist. Mit einer ersten Modellanwendung konnte gezeigt werden, dass über die Variabilität der Bodenparameter Trockenrohdichte und Tongehalt auch die Variabilität der Bodenhydraulik und damit die Berechnung des Bodenfeuchteverlaufs am Standort darstellbar ist. / The consideration of the spatial variability of the unsaturated soil hydraulic characteristics still remains an unsolved problem in the modelling of the water and matter transport in the vadose zone. This can be mainly explained by the rather cumbersome measurement of this variability, which is both, time-consuming and cost-intensive. The presented thesis analyses various measurement strategies which aim at the description of the soil-hydraulic heterogeneity by a small number of proxy-parameters, which should be easily measurable and still have a soil-physical meaning. The developed approach uses a similarity concept, which groups soils into similar soil hydraulic classes. Within a class, the variability of the retention and hydraulic conductivity curves can be explained by a single parameter (scaling parameter). The analysis of the correlation between the soil parameters and the scaling parameters can eventually indicate which soil parameters can be used for describing the soil hydraulic variability in a given area. This investigation forms the basis for the further development of a stochastic model, which can integrate the soil-hydraulic variability in the modelling of the soil water transport. Three data sets, all covering different scales, were subsequently used in the application of the developed concept. The results show that depth development of the soil-hydraulic variability in a soil profile can be explained by a single soil parameter. Contrarily, the explanation of the horizontal variability of the soil-hydraulic properties was not possible with the given data sets. First model applications for a soil profile showed that including the variability of the soil parameters bulk density and clay fraction in the water transport simulations could describe the variability of the soil-hydraulic variability and thus, the dynamics of the soil water content at the investigated profile.

<p>This study tested a dynamic modelling approach based on salt application, meteorological data and generic descriptions of hydrogeological environments for describing the spread of deicing salt to the surroundings and the corresponding increase in chloride storage in soil. Both the amount of chloride storage and the annual variation pattern were significantly altered due to deicing salt application and spread to the roadside environment. Data from field investigations comprising different hydrogeological environments and different methods of measurement were used to examine the variability of the salt deposition pattern in the vicinity of the road, and to test the performance of the model with respect to different soils and vegetation types. The use of typical hydrogeological environments to represent inputs to the model was shown to be useful to demonstrate the importance of soils, vegetation type and groundwater conditions for modelling the impact of deicing salt on soil water and the response to environmental changes in the vadose zone. However, the use of hydrogeological environment could also be misleading in view of the high degree of variability at the field scale. The different methods of measurements and simulations represented different spatial and temporal scales that were shown to be complementary useful to quantify the different pathways of deicing salt in the roadside environment. Continuous simulations complemented with selected field monitoring should therefore be promoted.</p> / QC 20100526

Agricultural management practices including tillage and irrigation have a considerable effect on soil physical and hydraulic properties in space and time. Tillage practices initially alter the soil physical and hydraulic properties depending on the type and depth of tillage. These changes are reverted back to original conditions due to reconsolidation during cycles of wetting and drying. Irrigation techniques can manipulate the reversion process dynamically due to different modes of wetting. The combined effects of tillage and irrigation have rarely been investigated. Therefore, two experiments were conducted to investigate the effect of different tillage practices and irrigation techniques on soil physical properties and temporal variations in soil hydraulic properties, one on wheat and second on the following maize crop grown on the same plots. The tillage and irrigation treatments implemented for the wheat crop were repeated for the subsequent maize crop restoring the same treatment layout plan. Intact soil core samples were collected, in the middle of the wheat crop before irrigation and the end of the maize crop season, for the determination of soil physical and hydraulic properties. Field saturated hydraulic conductivity (K_fs) was determined using the Guelph pressure infiltrometer method and volumetric soil water content (θ_v) and potential (ψ_m) was measured in the field using water content sensors and tensiometers, respectively. The wheat crop received rain showers from time to time, while in maize, a heavy spell of monsoon rains following tillage caused most of the soil reconsolidation. So, the greater intensity of rains, rather than the cycles of wetting and drying, became primarily responsible for the differences in soil physical and hydraulic properties between the two crops. Moldboard plow resulted in an increase in yield and improvement of soil hydraulic properties during both crop seasons. Flood irrigation reverted back the effects of tillage on soil hydraulic properties greater than sprinkler irrigation, while it did not affect the yield significantly. The dynamics of volumetric soil water content (θ_v) differed, depending on tillage type, irrigation technique and crop season. Moldboard plow was the wettest after rain or irrigation events but it dried quicker than other tillage treatments. Flood irrigation caused higher wetting than sprinkler irrigation. These wetting effects were greater in wheat as compared to maize crop. Temporal variability calculated as time averaged relative difference in θ_v was greater during wheat as compared to maize, while temporal stability calculated as standard deviation of temporal stability decreased with flood irrigation in both crops. Soil bulk density (ρ_b) and water retention characteristics (θ_v (ψ_m )) measured on the intact soil cores and total porosity (φ), plant available water capacity (θ_PAWC) and pore size distribution calculated from water retention data depended on the time of sampling. During wheat, the ρ_b was lower resulting in a higher φ than after maize. Moldboard plow decreased ρ_b increasing φ, while the effect of flood irrigation was opposite in both crops with greater magnitude in wheat. Similarly, the effects of tillage on θ_v (ψ_m ) were observed in both crops, while those of irrigation were observed in maize only. Cultivator treatment retained higher θ_v at higher ψ_m (−30 and −100 kPa), followed by chisel and moldboard plow. Plant available water capacity (θ_PAWC) was greater in maize as compared to the wheat crop. Cultivator had higher θ_PAWC than chisel and moldboard plow in both crops. Wheat had greater volume of larger pores (> 10 μm, φ_(>10)), whereas extraordinary rains as well as irrigations after tillage caused these larger pores to decrease in maize. Moldboard plow had higher φ_(>10) at 10 cm depth in both crops with greater magnitude in wheat. Field saturated hydraulic conductivity (K_fs) determined before irrigations and at the end of both crop seasons was greater in wheat than in maize especially in the first determination. Moldboard plow exhibited greater K_fs followed by chisel plow and cultivator in both crops and it decreased significantly with time in wheat but not in maize. Flood irrigation was responsible for a reduction in K_fs and the effect was greater in wheat as compared to maize. It was concluded that a greater intensity of water application in the form of rains or irrigations can revert the changes in soil physical and hydraulic properties induced by tillage more effectively than the cycles of wetting and drying. Soil hydraulic properties may be optimized with the combination of suitable tillage and irrigation for efficient utilization of water resources.

This study tested a dynamic modelling approach based on salt application, meteorological data and generic descriptions of hydrogeological environments for describing the spread of deicing salt to the surroundings and the corresponding increase in chloride storage in soil. Both the amount of chloride storage and the annual variation pattern were significantly altered due to deicing salt application and spread to the roadside environment. Data from field investigations comprising different hydrogeological environments and different methods of measurement were used to examine the variability of the salt deposition pattern in the vicinity of the road, and to test the performance of the model with respect to different soils and vegetation types. The use of typical hydrogeological environments to represent inputs to the model was shown to be useful to demonstrate the importance of soils, vegetation type and groundwater conditions for modelling the impact of deicing salt on soil water and the response to environmental changes in the vadose zone. However, the use of hydrogeological environment could also be misleading in view of the high degree of variability at the field scale. The different methods of measurements and simulations represented different spatial and temporal scales that were shown to be complementary useful to quantify the different pathways of deicing salt in the roadside environment. Continuous simulations complemented with selected field monitoring should therefore be promoted. / QC 20100526

Soil and agricultural management practices (AMP) that are able to provide for an increasing population while meeting environmental existential challenges have gained considerable attention in recent times. Such AMP influence the soil profile and hydrological components for varying depths and patterns, depending on site-specific and environmental conditions. Though it is well known that management-induced changes of soil structure have consequences on soil hydraulic properties (SHP) and water fluxes, their dynamics through a season or on a long-term basis are hardly studied. Typically, an invariant soil pore system is assumed when modeling the transport of water and solutes in the soil system which leads to incorrect predictions of the dynamics of water balance components. Ultimately, this may lead to poor decision making and mismanagement of environmental resources. Hence, the present study quantifies the dynamics of SHP from existing studies and evaluates a model that is able to capture soil pore space dynamics following tillage. The objectives were to (1) investigate the quantitative effects of agricultural practices on soil structure and hydraulic properties and the subsequent response of the water balance components (2) evaluate a pore space evolution model for its capability in predicting the evolution of soil pore size distribution (PSD) for two cases: a) when there is a change in the tillage regime and/or land-use change b) in the months following tillage (3) derive corresponding soil water retention and hydraulic conductivity functions to incorporate them in hydrological models To achieve these objectives, first, a review of contemporary literature was undertaken to analyze the impacts of anthropogenic and environmental influences on SHP. The analysis indicated the relevance of studying temporal alterations of soil structure and SHP. Thereafter, a numerical model was evaluated for its ability to capture the dynamics of soil pore space with respect to time and pore radius using water retention parameter data sets from different parts of the world. The physically based coefficients of the model simulated the processes that were expected to occur after tillage. Furthermore, saturated hydraulic conductivity was obtained from the initial and final pore size distributions. Using the final pore size distribution curve and water retention function, the hydraulic conductivity function was also derived. The resulting water retention and hydraulic conductivity curves can directly be used as input in hydrological modeling studies. The results of the literature review indicate that, generally, soils show an abundance of large pores immediately after tillage. Those pores are not stable with time mainly due to precipitation and biological activity. Saturated hydraulic conductivity decreases in periods of rainfall along with the number of macropores and the overall porosity. Thus, the infiltration rates and capacities also decrease. However, the results of existing studies cannot be generalized owing to discrepancies in the dynamics of SHP, infiltration rates and soil moisture dynamics for soils under similar agricultural management practices. They are attributed mainly to a lack of standardization of research methodology as well as to site-specific conditions. Furthermore, it was also seen that incorporating the temporal dynamics of SHP in hydrological models produce more reliable and accurate modeling outcomes in comparison to studies with constant SHP as model input. The evaluation of the pore evolution model illustrated its suitability in capturing the temporal dynamics of soil pore space in response to tillage and environmental influences. High effective rainfalls and plant growth stages at which measurements were done affected the model performance. The use of sink/source terms and providing new initial conditions after high intensity rainfall events were provided as a means to improve the modeling outcomes. Though the model performed quite well in obtaining the water retention function as well as the saturated hydraulic conductivity and hydraulic conductivity functions, the high spatial variability in the sampling sites hampered with the model output. However, the main limitation lay in the lack of availability of sufficient data sets to calibrate and validate the model and its coefficients as well as for the derivation of SHP from the model. Overall, this study is a forerunner in predicting the temporal dynamics of soil structure and hydraulic properties. The established dynamics in the water retention and hydraulic conductivity functions can be used in hydrological simulations for planning land-use and management measures. The current study also reveals the need for more measurements and data sets that capture the alterations in soil hydraulic properties on a long-term basis.