Saturated and near-saturated surface soil hydraulic properties influence the partition of rainfall and snowmelt into infiltration and runoff. The goal of this study was to characterize near-saturated surface soil hydraulic properties and water-conducting porosity in sloping landscapes. The specific objectives included exploration of tension and double-ring infiltrometers for estimation of soil hydraulic properties in sloping landscapes, development of an improved method for determining water-conducting porosity, and the application of these methods in characterizing soil hydraulic properties and water-conducting porosity under three land use. Water infiltration from a double-ring infiltrometer and a tension infiltrometer at water pressures between -2.2 and -0.3 kPa was measured in a cultivated field with 0, 7, 15, and 20% slopes at Laura and under three land use (native grass, brome grass and cultivated) at St. Denis in Saskatchewan, Canada. Three-dimensional computer simulation studies were also performed for tension infiltrometer with various disc diameters, water pressures, and surface slopes. Steady infiltration rates and estimated field-saturated hydraulic conductivity (Kfs), hydraulic conductivity-water pressure relationship (K(h)), and inverse capillary length parameter were compared for different slopes and land use. These parameters were not significantly different (p<0.05) among slopes. For specific K(h) functions, a new analytical solution was developed and compared with existing methods for calculating water-conducting porosity. The new method reliably determined water-conducting porosity of surface soils and gave consistent results, regardless of the width of water pressure ranges. At the -0.3 kPa water pressure, hydraulic conductivity of grasslands was two to three times greater than the cultivated lands. Values of inverse capillary length parameter were about two times and values of Kfs about four times greater in grasslands than in cultivated fields. Water-conducting macroporosity of grasslands and cultivated fields were 0.04% and 0.01% of the total soil volume, respectively. Over 40% and 50% of the total water flux at -0.06 kPa water pressure was transmitted through macropores (pores > 1×10-3 m in diameter) of the cultivated land and the grasslands, respectively. Experimental and simulation results of this study indicated that both tension and double-ring infiltrometers are suitable for characterization of saturated and near-saturated surface soil hydraulic properties in landscapes up to 20% slope. The new method can be used to characterize water-conducting porosity from in situ tension and double-ring infiltrometers measurements more adequately and efficiently than the existing methods. Application of these methods for three land use indicated that land use modified surface soil hydraulic properties and consequently may alter the water balance of an area by affecting the partition between, and relative amount of infiltration and surface runoff.

Saturated and near-saturated surface soil hydraulic properties influence the partition of rainfall and snowmelt into infiltration and runoff. The goal of this study was to characterize near-saturated surface soil hydraulic properties and water-conducting porosity in sloping landscapes. The specific objectives included exploration of tension and double-ring infiltrometers for estimation of soil hydraulic properties in sloping landscapes, development of an improved method for determining water-conducting porosity, and the application of these methods in characterizing soil hydraulic properties and water-conducting porosity under three land use. Water infiltration from a double-ring infiltrometer and a tension infiltrometer at water pressures between -2.2 and -0.3 kPa was measured in a cultivated field with 0, 7, 15, and 20% slopes at Laura and under three land use (native grass, brome grass and cultivated) at St. Denis in Saskatchewan, Canada. Three-dimensional computer simulation studies were also performed for tension infiltrometer with various disc diameters, water pressures, and surface slopes. Steady infiltration rates and estimated field-saturated hydraulic conductivity (Kfs), hydraulic conductivity-water pressure relationship (K(h)), and inverse capillary length parameter were compared for different slopes and land use. These parameters were not significantly different (p<0.05) among slopes. For specific K(h) functions, a new analytical solution was developed and compared with existing methods for calculating water-conducting porosity. The new method reliably determined water-conducting porosity of surface soils and gave consistent results, regardless of the width of water pressure ranges. At the -0.3 kPa water pressure, hydraulic conductivity of grasslands was two to three times greater than the cultivated lands. Values of inverse capillary length parameter were about two times and values of Kfs about four times greater in grasslands than in cultivated fields. Water-conducting macroporosity of grasslands and cultivated fields were 0.04% and 0.01% of the total soil volume, respectively. Over 40% and 50% of the total water flux at -0.06 kPa water pressure was transmitted through macropores (pores > 1×10-3 m in diameter) of the cultivated land and the grasslands, respectively. Experimental and simulation results of this study indicated that both tension and double-ring infiltrometers are suitable for characterization of saturated and near-saturated surface soil hydraulic properties in landscapes up to 20% slope. The new method can be used to characterize water-conducting porosity from in situ tension and double-ring infiltrometers measurements more adequately and efficiently than the existing methods. Application of these methods for three land use indicated that land use modified surface soil hydraulic properties and consequently may alter the water balance of an area by affecting the partition between, and relative amount of infiltration and surface runoff.

The underlying objective of this research is to improve the overall understanding of how spatial and temporal variability in macroporosity and soil hydraulic properties in the shallow subsurface influence the long term mobility of agricultural nutrients, and specifically the movement of liquid swine manure, in macroporous, tile drained soils. The principal motivation for the work was to provide insight into dynamic nutrient mobility in this type of agricultural environment in order to guide both the efficiency and environmental sustainability of nutrient management practices. The results of this work facilitate the advancement of our conceptual understanding and our ability to simulate preferential flow and transport in structured agricultural soils that are subject to seasonal hydrologic patterns similar to those found in the humid continental climate of southwestern Ontario

This thesis research consists of two separate studies. The first study presents the assessment and representation of the effects of soil macropores on the soil hydraulic properties in land surface models for more accurate simulations of soil moisture and surface hydrology. Hydraulic properties determine the soil water content and its transport in the soil. They are provided in most current climate models as empirical formulas by functions of the soil texture. Such is not realistic if the soil contains a substantial amount of macropores. A two-mode soil pore size distribution is incorporated into a land surface model and tested using an observational dataset at a tropical forest site with aggregated soils. The result showed that the existence of macropores greatly affects the estimation of hydraulic properties. Their influence can be included in land models by adding a second function to the pore-size distribution. A practical hydraulic scheme with macropore considerations was proposed given that the existing schemes are not applicable for large-scale simulations. The developed scheme was based on the physical attributes of the water in soil capillary pores and the statistics of several global soil databases. The preliminary test showed that it captures part of soil macropore hydraulic features without sacrificing the estimation accuracy of hydraulic properties of water in soil matrix. The second study presents the development of an integrated land/ecosystem model by combining the advanced features of a biophysically based land model, the Community Land Model, and an ecosystem biochemical model. The results from tests of the integrated model at four forest sites showed that the model reasonably captures the seasonal and interannual dynamics of leaf area index and leaf nitrogen control on carbon assimilation across different environments. With being coupled to an atmospheric general circulation model (AGCM), the integrated model showed a strong ability to simulate terrestrial ecosystem carbon fluxes together with heat and water fluxes. Its simulated land surface physical variables are reasonable in both geographic distribution and temporal variation with considering the interactive vegetation parameters.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2009. / Härtill 4 uppsatser.

The underlying objective of this research is to improve the overall understanding of how spatial and temporal variability in macroporosity and soil hydraulic properties in the shallow subsurface influence the long term mobility of agricultural nutrients, and specifically the movement of liquid swine manure, in macroporous, tile drained soils. The principal motivation for the work was to provide insight into dynamic nutrient mobility in this type of agricultural environment in order to guide both the efficiency and environmental sustainability of nutrient management practices. The results of this work facilitate the advancement of our conceptual understanding and our ability to simulate preferential flow and transport in structured agricultural soils that are subject to seasonal hydrologic patterns similar to those found in the humid continental climate of southwestern Ontario

Conservation tillage systems are increasingly adapted replacing conventional turnover moldboard plowing practices worldwide. This is part of a sustainable intensification of agriculture to meet future global food demand while at the same time sustaining environmental resources. The choice of tillage system affects soil structure and thereby also soil hydraulic properties (SHP) such as the water retention characteristic (WRC) and the hydraulic conductivity characteristic (HCC). Effects of agricultural management on SHP have been widely studied in the past decades. Thereby, temporal variations were identified as a major source of variability in the quantification of soil pore space and SHP. Such variability is introduced by tillage creating a loose soil matrix that eventually settles due to gravity, wetting-drying cycles and temperature fluctuations but also variable soil organic matter distributions in the soil and biological activity. Past efforts to model soil water dynamics showed that consideration of time-variable SHP may significantly improve simulation results. This involves both the seasonal variability as well as long-term land-use changes from conventionally to untilled soil. A prerequisite for such an approach is the periodic quantification of the WRC and HCC in the field and laboratory. In addition to the direct provision of modeling parameters, the quantification of WRC and HCC over time yields information on soil structural changes in the shape of a soil pore size distribution (PSD). The evolution of derived PSDs can be modeled and with that, the evolution of SHP might be predicted. However, there is little data available and the processes happening over one cropping season or between land-use changes need to be better understood. The aim of this dissertation was to shed light on soil pore space and associated hydraulic property changes on a long-term (23 years) tillage experiment in Eastern Germany. Three treatments with varying tillage intensity were investigated: conventional tillage with a turnover moldboard plow (CT), reduced mulch tillage with a cultivator (RT) and no tillage with direct sowing (NT). The soil was a Haplic Luvisol with silt loam texture. Objectives were twofold: • Objective 1) was to quantify the temporal variability in PSD over one winter wheat cropping season by frequently measuring SHP. Soil physical quality of the three treatments was assessed using this data. • Objective 2) was to characterize the soil structural differences between the treatments by relating hydraulic conductivity over a wide soil moisture range to other soil physical and chemical properties. For Objective 1), undisturbed soil cores (250 cm3) were taken over one winter wheat cropping cycle on five occasions from December 2015 to after the harvest in August 2016. Those soil cores were used to determine the saturated hydraulic and the WRC as well as the HCC in the laboratory. The data was parametrized with the bimodal Kosugi and Mualem model. Soil physical quality was assessed by the relative field capacity and air capacity as suggested in recent literature. Results showed that tilled soil, i.e. CT and RT, exhibited a distinct bimodal PSD with a structural and a textural mode. However, this structural mode was temporally instable and diminished after the winter and throughout the early growing season. Likely processes behind those changes were wetting-drying cycles, rainfall impact and freeze-thaw cycles. Shortly before and after the harvest some of the structural mode was restored which was probably induced by decomposing organic matter mixed into the topsoil from the previous winter wheat harvest during stubble breaking. Described changes were evident in decreases of transmission pores (⌀ 50 - 500 µm) during winter and increases during summer. Untilled soil, i.e. NT, tended towards a unimodal PSD with less transmission but more storage (⌀ 0.5 - 50 µm) pores. Temporally this soil was rather inert. This was attributed to natural compaction in absence of annual tillage for more than 20 years. Soil physical quality varied with the changes in PSD. Water availability was not an issue. Overall, the soil physical quality indicators for soil aeration were outside of an optimal range for indicators for most of the time. For Objective 2), field infiltration measurements were conducted with a hood (tension) infiltrometer to obtain (near-) saturated hydraulic conductivity. Soil cores were taken to quantify unsaturated hydraulic conductivity. Other properties for correlation and multiple regression analysis were bulk density, the bubbling pressure, organic C, as well as macro- and mesoporosity. X-ray µCT imaging on undisturbed soil cores from CT and NT treatments gave additional information on soil pore metrics. Results pointed towards a distinctly different soil structure between tilled and untilled soil. Near-saturated hydraulic conductivity of tilled soil was negatively correlated with bulk density as well as macro- and mesoporosity. None of the properties was meaningful for untilled soil. Imaging results confirmed the hypothesis, that (near-) saturated hydraulic conductivity on NT is governed by few well-connected large pores, while the soil matrix is comparably dense conducting only small amounts of infiltrating water. On tilled soil, the overall porosity is relevant for water transmission. Large continuous pore systems, however, get destroyed by annual tillage. In summary, the study showed distinct differences in soil structure and inherently also SHP between conservation and conventional tillage treatments. Differences in SHP, both in (near-) saturated hydraulic conductivity as well as WRC and HCC were large between some occasions. Therefore, this study confirmed the notion that on arable soils one-off measurements of SHP are not enough for their proper quantification. This was especially true for tilled soil. Modeling tasks over one cropping period, i.e. for example for irrigation schedules, will make periodic measurements necessary, i.e. unless an accurate modeling of the PSD becomes feasible. Current restraints are that most PSD models only consider a short-term post-tillage loss of porosity while a restored macropore system is not accounted for. In contrast to CT and RT, NT soil was temporally stable. While water retention was improved, (near ) saturated hydraulic conductivity was overall lower than on tilled soil. Correlation and regression analysis in combination with X-ray µCT explained some of the differences observed by tension infiltration measurements. Results highlighted that for arable soil, tillage treatments and probably other agricultural management practices, need to be considered when developing pedotransfer functions for an accurate estimation of SHP.:Table of Contents Declaration of conformity I Acknowledgements II Table of Contents IV List of Figures VII List of Tables XI Nomenclature XIII Abstract XV Zusammenfassung XVIII 1 Introduction 1 1.1 The sustainable development agenda and conservation tillage 1 1.2 Soil structure and soil hydraulic properties 3 1.3 Effects of conservation tillage on soil hydraulic properties 5 1.4 Temporal variability of soil hydraulic properties 8 1.5 Objectives and hypotheses 10 1.6 Structure of the dissertation 12 2 Materials and methods 15 2.1 Study area 15 2.1.1 Tillage experiment Lüttewitz (‘Schlag Gasthof’) 15 2.1.2 Treatments and agricultural management 16 2.2 Sample design 20 2.3 Field measurements 22 2.3.1 Hood infiltrometer measurements 22 2.3.2 Analysis of hood infiltrometer measurements 24 2.3.3 Macropore stability indicator 24 2.3.4 Undisturbed and disturbed soil sampling 25 2.4 Laboratory measurements 26 2.4.1 Saturated hydraulic conductivity 26 2.4.2 Water retention and hydraulic conductivity characteristic 26 2.4.3 Other soil properties 27 2.5 Model fitting procedure 28 2.5.1 Bimodal models for the water retention and hydraulic conductivity characteristic 28 2.5.2 Parametrization to quantify changes in the pore size distributions and pore volume fractions 29 2.5.3 Parametrization to infer unsaturated hydraulic conductivity for variability analysis 31 2.6 Capacitive soil physical quality indicators 32 2.7 Relationship between imaged pore metrics and field near-saturated hydraulic conductivity 32 2.8 Statistical analysis 33 3 Results 35 3.1 Rainfall patterns 35 3.2 Field (near-) saturated hydraulic conductivity 36 3.3 Threshold pore radius 37 3.4 Laboratory saturated hydraulic conductivity 38 3.5 Unsaturated hydraulic conductivity 39 3.6 Soil pore size distributions and pore volume fractions over one cropping season 40 3.7 Capacitive soil physical quality indicators 45 3.8 Correlation and linear regression of hydraulic conductivity with other soil properties 46 3.9 Other soil properties 49 3.9.1 Bulk density 49 3.9.2 Soil organic carbon and nitrogen 50 3.10 Imaged soil structure and hydraulic conductivity 52 3.10.1 Comparison of hydraulic conductivity obtained through three methods in Spring 2018 52 3.10.2 Soil pore metrics 52 3.10.3 Correlation between hydraulic conductivity and pore metrics 53 4 Discussion 55 4.1 Soil pore size distributions over one cropping cycle 55 4.1.1 Soil pore size distribution is bimodal on tilled soil and varies with time 55 4.1.2 Summary Objective 1) Hypotheses A and B 58 4.2 The effects of a changing pore system on soil physical quality 59 4.2.1 Suboptimal soil physical quality indicators change with time 60 4.2.2 Summary Objective 1) Hypothesis C 62 4.3 Tillage effects on variability of hydraulic conductivity 62 4.3.1 (Near ) saturated hydraulic conductivity 62 4.3.2 Unsaturated hydraulic conductivity 64 4.3.3 Summary: Objective 2) Hypothesis D and E 65 4.4 Factors influencing water transmission and its temporal variation 65 4.4.1 Soil properties partly explain variability in hydraulic conductivity on CT 65 4.4.2 Imaged pore metrics explain differences in field hydraulic conductivity 67 4.4.3 Summary Objective 2) Hypothesis F 68 5 Summary and outlook 69 References 73 Appendix 93

Good estimates of soil hydraulic parameters and their distribution in a catchment is essential for crop and hydrological models. Measurements of soil properties by experimental methods are expensive and often time consuming, and in order to account for spatial variability of these parameters in the catchment, it becomes necessary to conduct large number of measurements. Estimation of soil parameters by inverse modelling using observations on either surface soil moisture or crop variables has been successfully attempted in many studies, but difficulties to estimate root zone properties arise for heterogeneous layered soils. Although extensive soil data is becoming more and more available at various scales in the form of digital soil maps there is still a large gap between this available information and the input parameters needed for hydrological models. Inverse modeling has been extensively used but the spatial variability of the parameters and insufficient data sets restrict its applicability at the catchment scale. Use of remote sensed soil moisture data to estimate soil properties using the inverse modeling approach received attention in recent years but yielded only an estimate of the surface soil properties. However, in multilayered and heterogeneous soil systems the estimation of soil properties of different layers yielded poor results due to uncertainties in simulating root zone soil moisture from remote sensed surface soil moisture. Surface soil properties can be estimated by inverse approach using surface soil moisture data retrieved from remote sensing data. Since soil moisture retrieved from remote sensing is representative of the top 5 cm only, inversion of models using surface soil moisture cannot give good estimates of soil properties of deeper layers. Crop variables like biomass and leaf area index are sensitive to the deeper layer soil properties. The main focus of this study is to develop a methodology of estimation of root zone soil hydraulic properties in heterogeneous soils by crop model based inversion techniques. Further the usefulness of the radar soil moisture and leaf area index in retrieving soil hydraulic properties using the develop approach is be tested in different soil and crop combinations. A brief introduction about the soil hydraulic properties and their importance in agro-hydrological model is discussed in Chapter 1. Soil water retention parameters are explained in detail in this chapter. A detailed review of the literature is presented in chapter 2 to establish the state of art on the following: (i) estimation of soil hydraulic properties, (ii) role of crop models in estimating soil hydraulic properties, (iii) retrieval of surface soil moisture using water cloud model from SAR data, (iv) retrieval of leaf area index from SAR (synthetic aperture radar) data and (v) modeling of root zone soil moisture and potential recharge. The thesis proposes a methodology for estimating the root zone soil hydraulic properties viz. field capacity, wilting point and soil thickness. To test the methodology developed in this thesis for estimating the soil hydraulic properties and their uncertainty, three synthetic experiments were conducted by inversion of STICS (Simulateur mulTIdiscplinaire pour les Cultures Standard) model for maize crop using the GLUE (Generalized Likelihood Uncertainty Estimation) approach. The estimability of soil hydraulic properties in a layer-wise heterogeneous soil was examined with several sets of likelihood combinations, using leaf area index, surface soil moisture and above ground biomass. The robustness of the approach is tested with parameter estimation (model inversion) in two different meteorological conditions. The details of the numerical experiments and the several likelihood and meteorological cases examined are given in Chapter 3. The likelihood combination of leaf area index and surface soil moisture provided consistently good estimates of soil hydraulic properties for all soil types and different meteorological cases. Relatively wet year provided better estimates of soil hydraulic properties as compared with a dry year. To validate the approach of estimating root zone soil properties and to test the applicability of the approach in several crops and soil types, field measurements were carried out in the Berambadi experimental watershed located in the Kabini river basin in south India. The profile soil measurements were made for every 10 cm upto 1 m depth. Maize, Marigold, Sunflower, Sorghum and Turmeric crops were monitored during the four year period from 2010 to 2013. Crop growth parameters viz. leaf area index, above ground biomass, yield, phenological stages and crop management activities were measured/monitored at 10 day frequency for all the five crops in the study area. The details of the field experiments performed, the data collected and the results of the model inversion using the ground measured data are given in Chapter 4. The likelihood combination of leaf area index and surface soil moisture provided consistently lower root mean square error (1.45 to 2.63 g/g) and uncertainty in the estimation of soil hydraulic properties for all soil crop and meteorological cases. The uncertainty in the estimation of soil hydraulic properties was lower in the likelihood combination of leaf area index and soil moisture. Estimability of depth of root zone showed sensitivity to the rooting depth. Estimating root zone soil properties at field plot scale using SAR data (incidence angle 24o, wave length 5.3 GHz) of RADARSAT-2 is presented in the Chapter 5. In the first step, an approach of estimating leaf area index from radar vegetation index using the parametric growth curve of leaf area index and the retrieval of soil moisture using water cloud model are given in Chapter 5. The parameters of the growth curve and the leaf area index are generated using a time series of RADARSAT-2 for two years 2010-2011 and 2011-12 for the crops (maize, marigold, sunflower, sorghum and turmeric) considered in this study. The surface soil moisture is retrieved using the water cloud model, which is calibrated using the ground measured values of leaf area index and surface soil moisture for different soils and crops in the study area. The calibration and validation of LAI and water cloud models are discussed in this Chapter. Eventually, the retrieved leaf area index and surface soil moisture from RADARSAT-2 data were used to estimate the soil hydraulic properties and their uncertainty in a similar manner as discussed in Chapter 4 for various crop and soil plots and the results are presented in Chapter 5. The mean and uncertainty in the estimation of soil hydraulic properties using inversion of remote sensing data provided results similar to the estimates from inversion of ground data. The estimates of soil hydraulic properties compared well (R2 of 0.7 to 0.80 and RMSE of 2.1 to 3.16 g/g) with the physically measured vales of the parameters. In Chapter 6, root zone soil moisture and potential recharge are modelled using the STICS model and the soil hydraulic parameters estimated using the RADARSAT-2 data. The potential recharge is highly sensitive to the water holding capacity of rooting zone. Variability in the root zone soil moisture for wet and dry years for different soil types on irrigated and non-irrigated crops were investigated. Potential recharge from different crop and soil types were compared. The uncertainty in the estimation of potential recharge due to uncertainty in the estimation of field capacity is quantified. The root zone soil moisture modeled by STICS showed good agreement with the measured root zone soil moisture in all crop and soil cases. This was tested for both dry and wet year and provides similar results. The temporal variability of root zone soil moisture was also modeled well by the STICS model; the model also predicted well the intra-soil variability of soil moisture of root zone. The results of the modeling of root zone soil moisture and potential recharge are presented in Chapter 6. At the end, in Chapter 7, the major conclusions drawn from the various chapters are summarized.

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

The knowledge of the dynamics of soil water is essential in agricultural, hydrological and environmental engineering as it controls plant growth, key hydrological processes, and the contamination of surface and subsurface water. Nearby remote sensing can be used for characterizing non-destructively the hydrogeophysical properties of the subsurface. In that respect, ground penetrating radar (GPR) constitutes a promising high resolution characterization tool. However, notwithstanding considerable research has been devoted to GPR, its use for assessing quantitatively the subsurface properties is constrained by the lack of appropriate GPR systems and signal analysis methods. In this study, a new integrated approach is developed to identify from GPR measurements the soil water content and hydraulic properties governing water transfer in the subsurface. It is based on hydrodynamic and electromagnetic inverse modeling. Research on GPR has focused on GPR design, forward modeling of GPR signal, and electromagnetic inversion to estimate simultaneously the depth dependent dielectric constant and electric conductivity of the shallow subsurface, which are correlated to water content and water quality. The method relies on an ultrawide band stepped frequency continuous wave radar combined with an off-ground monostatic TEM horn antenna. This radar configuration offers possibilities for real time mapping and allows for a more realistic forward modeling of the radar-antenna-subsurface system. Forward modeling is based on the exact solution of Maxwell's equations for a stratified medium. The forward model consists in elementary linear components which are linked in series and parallel. The GPR approach is validated for simple laboratory and outdoor conditions. GPR signal inversion enables the monitoring of the soil water dynamics, which can be subsequently inverted for estimating the soil hydraulic properties. A specifically designed hydrodynamic inverse modeling procedure which requires only water content data as input is further developed and validated to obtain the soil hydraulic properties under laboratory conditions.