Applied Soil Hydrology

Frontmatter

Chapter 1. Soil as a Part of the Soil–Plant–Atmosphere Continuum (SPAC)

Abstract

Soil is a part of the Soil–Plant–Atmosphere Continuum (SPAC); water and energy are transported mostly through all three parts of the SPAC system, but in the case of bare soil or the water table, the SPAC system is reduced to the Soil–Atmosphere Continuum (SAC) or to the Water-Table–Atmosphere Continuum (WAC). This chapter contains basic information about all three subsystems of SPAC. Conceptual approaches to the soil-water and energy transport are defined, as well as the representative elementary volume of soil (REV) needed to measure soil characteristics. The basic characteristics and properties of water (water vapour), soil, plant canopy and atmosphere are presented and their role in water and energy transport in the SPAC system is discussed. Soil water is always a low concentrated solution, but its physical properties are not changed significantly, and therefore it can be assumed to be clean water. The solute concentration is considered to evaluate the increased risk of soil salinization. The role of carbon dioxide in the SPAC system and its role in climate change are discussed.

Viliam Novák, Hana Hlaváčiková

Chapter 2. Basic Physical Characteristics of Soils

Abstract

Soil as a specific type of porous media known as a capillary porous medium is described, and its basic physical properties are defined. Because soil is a three-phase system, composed of solid, liquid and gaseous components, the basic properties of all three phases are described and quantified. Definitions of soil porosity, specific bulk density, bulk density, aeration, soil water content and soil specific surface are presented. Soil texture is defined and methods of soil texture (mechanical composition) determination are described (sieving, sedimentation method, pipette method, hydrometric method, laser-diffraction method) and their specific features are briefly mentioned. Pedogenetic factors and processes and their role in soil pedogenesis of various soil types are described, as well as their role in the formation of soil physical properties. The influence of clay minerals in soil physical properties formation and mechanisms of their interaction with soil water are demonstrated.

Viliam Novák, Hana Hlaváčiková

Chapter 3. Physical Properties of Water

Abstract

Water covers more than two third of Earth’s surface and thus is the most prevalent substance on Earth. It is also the only liquid on Earth occurring simultaneously in all three phases: ice, liquid water and water vapour. Its dynamics are linked to the great expenditure of energy to keep in motion ‘the water cycle and thus stabilize Earth’s climatic conditions. Water’s occurrence and its movement are preconditions for biomass production. In this chapter, the physical properties of water are quantitatively described to enable a calculation of its transport in the hydrosphere. Moreover, the molecular structure of water that determines water’s physical and transport properties is treated. Soil water is characterized as a solution of solute low concentration, and the solubility of gas in water is defined and quantified. Water density, compressibility and expansion, as well as water’s surface tension and viscosity are defined, and their dependence on temperature is explained.

Viliam Novák, Hana Hlaváčiková

Chapter 4. Soil-Water Interface Phenomena

Abstract

Capillarity in porous media (soils) is the basic physical phenomenon responsible for soil-water retention. Without this solid-water interface phenomenon, soil water is transported downward by the force of gravity, thus moving water from precipitation through the top layer of soil to groundwater. Water retention and plant growth would be profoundly limited. In this chapter, capillarity as an important physical phenomenon is described, and the height of the capillary-rise formula is presented. A simplified model of soil as a bundle of capillary tubes is used to explain soil-water behaviour in real soils. The influence of the shape of water menisci on water-vapour pressure just above menisci and capillary-condensation phenomenon are explained. Adsorption and desorption isotherms and the influence of clay minerals on adsorption and desorption phenomena are also mentioned.

Viliam Novák, Hana Hlaváčiková

Chapter 5. Soil-Water Content and Its Measurement

Abstract

Soil-water content is the basic state characteristic of soil; it expresses the relative quantity of water in the soil. Soil-water content can be expressed as the ratio of water amount and the amount of soil. The most frequently used term is volumetric soil-water content, which is the ratio of water volume and soil volume containing water. Mass soil-water content is expressed as the ratio of water mass and mass of dry soil containing water. Measuring soil-water content is the basic procedure in soil research. Methods for the measurement of soil-water content are briefly described. The basic method is the gravimetric method, a measuring procedure involving only weighing; it is also the reference method of soil-water content measurement, therefore it is described in detail and its weak points (soil—profile destruction and its nature as a discontinuous type of measurement) are discussed. Wide varieties of methods with continuous output are briefly described; neutron method, capacitance method, electrical resistance method, time-domain reflectometry (TDR), frequency-domain reflectometry (FDR), and geophysical and remote-sensing methods.

Viliam Novák, Hana Hlaváčiková

Chapter 6. Soil-Water Potential and Its Measurement

Abstract

Soil-water potential expresses quantitatively the energy of soil water (of water in porous medium); the difference between soil-water potentials of two points is necessary a condition to transport soil water from the point of higher to the point of lower soil-water potential. In this chapter, soil-water potential is defined and expressed as a negative value because of binding forces between soil and water. Total soil-water potential and its components (gravitational, matric and pneumatic) are defined, and principles of methods of their measurement are described. The principles underlying piezometer measurement of positive pressure potentials and tensiometer measurement of soil-matric potentials are analyzed, and the techniques of their application in the field are discussed.

Viliam Novák, Hana Hlaváčiková

Chapter 7. Soil-Water Retention Curve

Abstract

Soil/water retention curve (SWRC) is the relationship between soil/water matric potential and volumetric soil-water content at equilibrium above the reference (zero) level represented by the free water table at atmospheric pressure. SWRC is the basic soil characteristic needed as input data for simulation models. SWRCs have a hysteresis-like character, i.e. this relationship is different for drying and wetting processes. Methods for SWRC measurement are described (pressure method, method of hanging column, psychrometric method, adsorption and desorption methods), as well as methods for their evaluation from measured data. Analytical expressions of the SWRC are presented and evaluations of useful “hydrolimits” like monomolecular water capacity, wilting point, available water capacity and field capacity using SWRC data are described.

Viliam Novák, Hana Hlaváčiková

Chapter 8. Soil-Water Movement in Water-Saturated Capillary Porous Media

Abstract

The movement of water through capillary porous media (soils) saturated with water is quantitatively described by the Darcy equation; its application to water flow and water-potential distribution for various configurations of soil samples is described. The Darcian approach to saturated soil-water movement assumes the porous space is fully saturated with water; the soil pores do not change their dimensions, and soil temperature is constant. Hydraulic conductivity and permeability of soils saturated with water are defined and a wide variety of its measurement methods is presented. The frequently used methods for the measurement of the saturated hydraulic conductivity of soil samples in the laboratory are described in detail. Field methods for the measurement of saturated hydraulic conductivity above the groundwater table are presented and discussed. Pedotransfer functions to evaluate hydraulic conductivity from available data are briefly discussed.

Viliam Novák, Hana Hlaváčiková

Chapter 9. Water in Unsaturated Soil

Abstract

Water in soil usually fills soil pores only partially, therefore soil unsaturated with water is the prevailing state of soil. The soil unsaturated with water is a necessary condition for the majority of the plants that grow in the environmental conditions of Europe. The diagnosis and prognosis of the soil-water regimen is necessary to manage the soil-water content to reach maximum yields. This chapter defines the basic hydrophysical characteristics of an unsaturated zone of soil; the relationship between soil-water matric potential and volumetric soil-water content (so-called retention curve) and soil hydraulic conductivity as a function of soil-water matric potential and methods of their estimation are described. The Darcy–Buckingham equation is presented, as well as the equation of Richards that describes transport of liquid water in unsaturated soil. The transport of water vapour in the unsaturated soil is quantified by soil-water diffusivity, as well as by the coefficient of water-vapour diffusion of the soil, which is quantitatively described too.

Viliam Novák, Hana Hlaváčiková

Chapter 10. Infiltration of Water into Soil

Abstract

Infiltration is the process of water entry into soil; it is the basic process supplying the soil root zone with water. Infiltration as a process can be divided into two basic types: rain infiltration and ponding infiltration (infiltration from ponds on the soil surface). Infiltration (and cumulative infiltration) curves of both types of infiltration are described and expressed by empirical and analytical functions proposed by Philip. Special attention is devoted to the Green and Ampt approach to quantify infiltration because of its simplicity and clear physical interpretation of the process. The influences of the rain rate, entrapped air, initial soil-water content and layered soil profile on infiltration dynamics are discussed. Methods for the estimation of the soil hydraulic conductivity using the infiltration process in the field are described as well.

Viliam Novák, Hana Hlaváčiková

Chapter 11. Redistribution of Water in Homogeneous Soil

Abstract

The post-infiltration process of water movement in the soil root zone is known as soil-water redistribution. Understanding the redistribution process is important to prevent infiltrated water to penetrate below the soil root zone and thus decrease the amount of soil-water available for plants and increase the risk of groundwater pollution. The process of soil-water redistribution is described, as well as the influence of soil properties and boundary/initial conditions on the rate of redistribution. The quantification of the redistribution process by the solution of the Richards equation assuming constant hydraulic conductivity of soil demonstrates the logarithmic decrease of soil-water movement during redistribution, thus preserving soil water for plants.

Viliam Novák, Hana Hlaváčiková

Chapter 12. Interaction of Groundwater and Soil Water

Abstract

Groundwater and soil water can interact if the groundwater is relatively close to the soil root zone. Transport of water between groundwater and soil water can significantly improve the supply to plants of water and nutrients. A groundwater depth of about two metres below the soil surface is assumed to be the critical depth that contributes markedly to the supply of water to the plant canopy. In this chapter, the vertical transport of water from groundwater to the root zone of the soil is quantified. It depends on the soil hydraulic properties and on the depth of the groundwater table below the hypothetical level of water extraction by plant roots and on the soil-water matric potential at the same level. Internal drainage of the soil profile as a result of a lowering of the groundwater table is quantitatively expressed. The drainage equations are derived to calculate the parameters of the systematic drainage system: the depth, horizontal distance and diameter of pipe drains in a homogeneous soil under conditions of steady and unsteady drainage.

Viliam Novák, Hana Hlaváčiková

Chapter 13. Evaporation

Abstract

Evapotranspiration is the most important term among the “sink” terms of the soil-water balance equation. In this chapter are described contemporary methods for evapotranspiration estimation, as well as the calculation methods to estimate its structural components: evaporation and transpiration. The basic equations of potential evapotranspiration calculation (the Penman equation) and actual evapotranspiration calculation (the Penman–Monteith equation) are presented, and their applications are described. The FAO modification of the Penman–Monteith equation to evaluate daily and hourly reference evapotranspiration is also presented. This chapter also contains the most popular empirical equations for the calculation of the potential evapotranspiration of various evaporating surfaces. Results of measurements of root-extraction patterns and proposed calculation methods for root water-uptake functions needed in mathematical models are briefly discussed.

Viliam Novák, Hana Hlaváčiková

Chapter 14. Transport of Solutes in Soils

Abstract

Soil water is in fact a solution; but in the majority of cases, the concentrations of soil solutes are small, and therefore soil-water physical characteristics are treated as the characteristics of pure water. Pollution transport, transport of dissolved fertilizers in infiltration water or transport of solutes in salt-affected soils should be treated as transport of solutions. Concentration of a solute is defined, and transport mechanisms of dissolved compounds in soil are described qualitatively and quantitatively in this chapter. Diffusion, convection and hydrodynamic dispersion are involved together with the continuity equation to derive the convective–diffusion transport equation. The Péclet number is used to evaluate the transport mechanisms of dissolved compounds. Outflow and breakthrough curves are defined, described and explained to identify the character and significance of the solute transport.

Viliam Novák, Hana Hlaváčiková

Chapter 15. Water and Energy Balance in the Field and Soil-Water Regimen

Abstract

Management of soil water to optimize biomass production is the primary aim of amelioration activities. Soil-water management, i.e. the design and operation of irrigation and drainage systems in the field have to be based on diagnoses of soil-water regimen. The soil-water regimen is a statistical characteristic of individual (mostly annual) cyclic courses of soil water (or soil-water matric potential); it is the generalisation of the individual annual courses by processing long-time (many years) average values of regimen characteristics. Then, the type of soil-water regimen and ways to manage it can be proposed and an expected yield can be calculated. Based on analysis of soil-water balance equations, one can propose the principles of soil-water management. Hydrological classification of the soil-water regimen and the principles of soil-water regimen diagnostics are presented.

Viliam Novák, Hana Hlaváčiková

Chapter 16. Swelling and Shrinking Soils

Abstract

Soils containing clay minerals (illite, montmorillonite) changing their volumes with soil-water content variation. Soil-water content decreases are followed by soil shrinkage, and increases in soil-water content is followed by swelling. These phenomena are expressed by the creation or closing of soil cracks, and the soil surface decreases/increases simultaneously. Soil cracks can be characterized by crack porosity, by their specific volume and by the specific surface; nets of cracks on the soil surface can be characterized by their specific length. An equilibrium relationship of crack porosity to soil-water content is typical of any particular soil. Soil cracks characterised by their volume and surface play an important role in water infiltration into dry, heavy soils; they significantly increase the retention volume of such soils and the infiltration surface of water-filling soil cracks. The importance of water infiltration into the soil matrix from cracks surface is demonstrated.

Viliam Novák, Hana Hlaváčiková

Chapter 17. Stony Soils

Abstract

This chapter provides a basic overview of the properties of stony soils: their main differences compared to non-stony soils, their occurrence, classification, basic physical and hydrophysical properties, as well as the methodology for their quantification, sampling methods, measurement of the hydrophysical properties of stony soils and the definition of so-called effective parameters needed for water-flow modelling in stony soils. The chapter also contains links to the latest literature in this area. An illustrative example of the evaluation of effective stony-soil parameters for particular stony soil from the Western High Tatra Mts. (Slovakia) and results of the illustrative water-flow modelling in the stony soil (a case study) are presented and discussed.

Viliam Novák, Hana Hlaváčiková

Chapter 18. Water Repellent Soils

Abstract

Capillary forces in unsaturated soils depend on the surface tension of water, the dimensions of soil pores and on the contact angle of the interfaces of the solid phase of soil (soil matrix) and liquid water. The contact angle (angle of wetting) is assumed to be zero, but in real soils is higher, depending on the properties of the thin surface layer (organic) covering soil particles. There are some classes of soils with limited affinity for soil water. Soils are classified as wettable with contact angles φ < 90°; water-repellent soils are characterized by contact angles of φ ≥ 90°. The occurrence of water-repellent soils is rare and usually their repellency is temporary (dry soils). This chapter defines the characteristics of soil-water repellency: contact angle, severity of water repellency, persistence of soil water repellency and index of water repellency. It also presents the hydrophobic compounds in soils and the influence of soil-water repellency on hydrological processes in soil (infiltration, preferential flow, evaporation).

Viliam Novák, Hana Hlaváčiková

Chapter 19. Soil Air and Its Dynamics

Abstract

Soil air as a part of the unsaturated zone of soil is a necessary soil constituent for the growth of the majority of plants. Oxidation of assimilates (respiration) is necessary for biomass production, and oxygen is also needed for the respiration of living organisms in soil. The composition of soil air is close to that of the atmosphere because small deficits of oxygen and a surplus of carbon dioxide are quickly equilibrated by air interchanges with an atmosphere. This chapter analyses the convection and diffusion of air in the soil and expresses them quantitatively. It also quantifies oxygen transport to the plant roots to cover respiration by solving the simplified transport equation. The influence of the oxygen diffusion rate on plant canopy growth is also presented.

Viliam Novák, Hana Hlaváčiková

Chapter 20. Soil Temperature and Heat Transport in Soils

Abstract

Soil temperature varies over a wide range, depending on annual and diurnal cycles of incoming solar energy and on the soil surface properties. Plants can grow when soil root zone temperatures are in the relatively narrow range 0–40 °C. Soil-water hydraulic conductivity and soil-water retention curves are functions of temperature because of the temperature dependence of viscosity, surface tension and the density of water. Characteristic annual and diurnal cycles of soil temperature (at various depths) characterise the soil-temperature regimen. This statistical characteristic is typical of particular soils and depends on climate. The basic soil-heat characteristics (specific soil heat capacity, thermal conductivity) and basic modes of heat transport, namely, conduction, convection and radiation, are defined. The chapter presents governing equations of simultaneous heat and water transport in non-isothermal soil conditions. The influence of soil temperature on basic soil-water transport and retention characteristics are addressed.

Viliam Novák, Hana Hlaváčiková

Chapter 21. Modelling of Water Flow and Solute Transport in Soil

Abstract

The chapter presents the basic state of the art of water flow and solute transport modelling in unsaturated zone of soil. It provides a brief overview of model development and categorisation according to various criteria. The governing equations of water flow and solute transport, the time and space discretization of the computing domain, the initial and boundary conditions, the necessary input data and model outputs are presented. The chapter includes a short description of the most popular models of water and energy transport in variably saturated porous media. The challenges regarding the modelling of water flow, solute transport and marginally of other soil processes in the soil, along with references, are also mentioned.

Viliam Novák, Hana Hlaváčiková

Backmatter