Improving agricultural water management is important for conserving water during dry seasons, using limited water resources in the most efficient way, and minimizing environmental risks (e.g., leaching, surface runoff). The understanding of water movement in different zones of agricultural production fields is crucial to developing an effective irrigation strategy. This work centered on optimizing field water management by characterizing the spatial patterns of soil hydraulic properties. Soil hydraulic conductivity was measured across different zones in a farmer’s field, and its spatial variability was investigated by using geostatistical techniques. Since direct measurement of hydraulic conductivity is time-consuming and arduous, pedo-transfer functions (PTFs) have been developed to estimate hydraulic conductivity indirectly through more easily measurable soil properties. Due to ignoring soil structural information and spatial covariance between soil variables, PTFs often perform unsatisfactorily when field-scale estimations of hydraulic conductivity are needed. The performance of PTFs in estimating hydraulic conductivity in the field was therefore critically evaluated. Due to the presence of structural macro-pores, saturated hydraulic conductivity (Ks) showed high spatial heterogeneity, and this variability was not captured by texture-dominated PTF estimates. However, the general spatial pattern of near-saturated hydraulic conductivity can still be reasonably generated by PTF estimates. Therefore, the hydraulic conductivity maps based on PTF estimates should be evaluated carefully and handled with caution. Recognizing the significant contribution of macro-pores to saturated water flow, PTFs were further improved by including soil macro-porosity and were proven to perform much better in estimating Ks compared with established PTFs tested in this study. Additionally, the spatial relationship between hydraulic conductivity and its potential influencing factors were further quantified by the state-space approach. State-space models outperformed current PTFs and effectively described the spatial characteristics of hydraulic conductivity in the studied field. These findings provided a basis for modeling water/solute transport in the vadose zone, and sitespecific water management.

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.

<p><font face="TimesNewRoman"> <p align="left">Research findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers.</p> </font></p>

<p><font face="TimesNewRoman"> <p align="left">Research findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers.</p> </font></p>

[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.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The soils of the Central Depression in Rio Grande do Sul consist mainly of mudstones, siltstones and sandstones. The region has dimensions ranging from 40 to 100 m at lower elevations (lowland) predominate Gley soils (shallow, poor drainage). In the plateau predominate Ultisols (deep to very deep and vary in color, as drainage level). The aim of this study was to evaluate the compressive behavior (carrying capacity and susceptibility to compaction) of the soil and influence of loads 25, 50, 100 and 200 kPa in the physical properties and water (CRA and air permeability). The sampling of soil for study was made in a private property located in Santa Maria. Trenches were dug to collect in two profiles located in the floodplain (Haplic Gley soil), two slopes (lower and upper) and one at the top, both Ultisol. In metal rings were collected soil samples with preserved structure for the uniaxial compression test on all horizons of the five different profiles, loads of 25, 50, 100 and 200 kPa in uniaxial press, then were only collected samples of soil surface horizons of the profiles for testing air permeability and water retention curve.. In both times the samples were equilibrated at a voltage of 10 kPa. Were carried out: sieve analysis, organic carbon, density, porosity, macro porosity, compressibility test, air permeability and water retention curve (WRC). The pre-consolidation pressure (σp) had a significant positive correlation with clay and negatively with sand, having no significant correlation with organic carbon (OC), degree of saturation (DS), voids (IV) and density (BD), the IC has had a significant negative correlation only with the Ds. Among the profiles, Gley Soils presented higher carrying capacity than the Argisols. Surface horizons had lower deformation compression curves compared to the subsurface, due to having larger soil density and smaller IV. The deeper horizons (BA, Bt1, Bt2 and Cg) showed higher σp than the surface horizons (A, Ap, A1, A2, B), by having greater amount of clay. The higher the load applied on the samples, higher soil density and porosity. The higher permeability was greater in profiles A, A1 and Ap under loads of 25 and 50 kPa, it produced no adverse effects on the structure. The application of higher loads in the sample changed the soil structure, retaining more water due to the increase of macro porosity. The Gley soils had a higher carrying capacity and are less susceptible to compaction than Argisols. Among Gley soil, profile 2 is less susceptible to compaction than a profile from the Ultisols and susceptibility to compaction of the profile 5 is lower than in profiles 3 and 4. The deeper horizons had higher pre-consolidation pressure (σp) and carrying capacity of the soil surface, because the greatest amount of clay. Loads of 25 and 50 kPa are lower than the values of pressure pre consolidation of horizons and the samples submitted showed no negative effects on the structure and had higher values of permeability. The application of loads 100 and 200 kPa, in the profiles 1.2 (floodplain), 4 (upper slope) and 5 (top) reduced the values of permeability, resulting from the change of the sample. The compacting process of the sample reduced macro porosity and increased total porosity by promoting greater water storage in the highest voltages applied. / Os solos da Depressão Central Gaúcha são constituidos porareia, silte e argila. A região tem cotas entre 40 à 100 m, nas mais baixas (várzea) predominam os Gleissolos e nas coxilhas predominam os Argissolos. O objetivo deste trabalho foi avaliar o comportamento compressivo (capacidade de suporte e susceptibilidade a compactação) do solo, e a influência de cargas 25, 50, 100 e 200kPa nas propriedades físicas e hídricas (curva de retenção de água (CRA) e permeabilidade ao ar (Ka)). As coletas de solo foram feitas em uma propriedade particular em Santa Maria, RS. Foram abertas trincheiras em dois perfis localizados na várzea (Gleissolos Háplicos), dois na encosta (inferior e superior) e um no topo, ambos Argissolo Vermelho. Foram coletadas amostras de solo com estrutura preservada em anéis metálicos para o teste de compressão uniaxial em todos os horizontes dos cinco diferentes perfis, após foram coletados somente amostras dos horizontes superficiais para os testes de Ka e CRA, após aplicadas as cargas de 25, 50, 100 e 200 kPa na prensa uniaxial. Nos dois momentos as amostras foram equilibradas à tensão de 10 kPa. Foram realizadas análise granulométrica, carbono orgânico, densidade, porosidade total, macroporosidade, microporosidade, teste de compressibilidade, Ka e CRA. A pressão de pré-consolidação (σp) teve correlação significativa positiva com a argila e negativa com a areia, não tendo correlação significativa com carbono orgânico (CO), grau de saturação (GS), índice de vazios (IV) e densidade do solo (Ds), o IC teve correlação significativa negativa somente com a Ds. Os Gleissolos apresentaram maior capacidade de suporte do que os Argissolos. Os horizontes superficiais tiveram menor deformação em relação aos subsuperficiais, devido a ter maior Ds e menor IV. Os horizontes mais profundos(BA, Bt1, Bt2 e Cg) apresentaram maior σp que os horizontes superficiais(A, Ap, A1, A2, AB), por terem maior quantidade de argila. Quanto maior a carga aplicada nas amostras, maior a densidade Ds e menos PT, a maior permeabilidade foi nos perfis A, A1 e Ap sob as cargas de 25 e 50 kPa, pois não produziram efeitos negativos na estrutura. A aplicação de maiores cargas na amostra mudou a estrutura do solo, retendo mais água em função do aumento de mircoporos. Os Gleissolos apresentaram maior capacidade de suporte e são menos suscetíveis à compactação do que os Argissolos. Os Gleissolos apresentaram maior capacidade de suporte e são menos suscetíveis à compactação do que os Argissolos. Dentre os Gleissolos, o perfil 2 apresentou menor susceptibilidade a compactação do que o perfil 1 e dentre os Argissolos, a susceptibilidade à compactação do perfil 5 é menor que nos perfis 3 e 4. Os horizontes mais profundos (BA, Bt1, Bt2 e Cg) apresentaram maior (σp) e capacidade de suporte que os horizontes superficiais (A, Ap, A1, A2 e AB) pois tem maior quantidade de argila. Após aplicação das cargas de 100 e 200 kPa, os perfis 1,2, 4 e 5 apresentaram menores valores de Ka, resultado da mudança de estrutura da amostra, diminuindo a macroporosidade e aumentando a microporosidade. A compactação da amostra reduziu a macroporosidade e a porosidade total promovendo um maior armazenamento de água nas maiores tensões aplicadas.

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

Philosophiae Doctor - PhD / Research findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers.

Philosophiae Doctor - PhD / Research findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers.

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