TXT Soil Water and Its Management Flashcards

Exactly 150 vocabulary flashcards based on the lecture notes on soil water management.

Turgidity

The tissue rigidity in plants maintained by water within the cells.

Transpiration

The process of water loss from microscopic openings in plant leaves known as stomata.

Stomata

Microscopic openings in leaf surfaces that facilitate the exchange of $CO_2$ and $O_2$ with the atmosphere.

Photosynthesis

The process of building carbohydrates using $CO_2$ and water, during which $O_2$ is expelled.

Xylem

The plant tissue through which roots draw up water from the soil to reach the leaves.

Integrated Water Resources Management (IWRM)

A systematic process for the sustainable development, allocation, and monitoring of water resource use in social, economic, and environmental contexts.

Soil water management

The collective practices of irrigation, improvement of natural drainage, and soil water conservation.

Soil water balance equation

Represented as $\Delta\Theta = P + I + C - E - T - D - R$ for the root zone.

$$\Delta\Theta$$

The change in soil moisture content during a given period in the soil water balance equation.

$P$ (Precipitation)

A gain term in the soil water balance representing natural water falling from the sky.

$I$ (Irrigation)

A gain term in the soil water balance representing water artificially supplied to the crop.

$C$ (Capillary rise)

A gain term in the soil water balance representing water moving upward from deeper zones to the root zone.

$E$ (Soil evaporation)

A loss term in the soil water balance representing water lost from the soil surface to the atmosphere.

$T$ (Transpiration)

A loss term in the soil water balance representing water returned to the atmosphere via plant stomata.

$D$ (Deep drainage)

A loss term in the soil water balance representing water flowing vertically out of the reach of plant roots.

$R$ (Runoff or Runon)

A term in the soil water balance representing surface and subsurface flow that can be either a gain (runon) or a loss (runoff).

Interception loss

Precipitation intercepted by vegetation that evaporates back into the atmosphere without reaching the ground.

Throughfall

The portion of precipitation that drips off vegetation to reach the ground surface.

Stemflow

Water that reaches the ground by flowing down the stems or tree trunks of plants.

Infiltration rate

The amount of water per unit area per unit time that enters the soil surface.

Infiltrability

Also known as infiltration capacity, it is determined by the initial soil moisture conditions and the water permeability of the soil surface layer.

Saturated hydraulic conductivity ($K_{s}$)

The steady-state rate at which soil accepts water when the topsoil reaches full saturation.

Surface storage capacity

The total volume of surface depressions where excess water first collects before runoff occurs.

Surface water flow

Another name for runoff, used to distinguish it from below-ground lateral flow.

Interflow

Below-ground lateral flow where water accumulated within topsoil layers moves laterally along a slope.

Groundflow

Below-ground lateral water flow that occurs below the level of the water table.

Redistribution

The process of downward water movement in a soil profile in the absence of a groundwater table.

Internal drainage

The process of downward water movement in a soil profile when a groundwater table is present.

Seepage

Another term for deep drainage, referring to water flowing out of the root zone toward deeper substrate layers.

Groundwater table (GWT)

The upper surface of the zone in the soil where all pores are completely filled with water.

Perched water table

Saturated soil conditions occurring above an impermeable layer like a hardpan, even if lower horizons are not saturated.

Surface tension (\sigma)

The enhancement of intermolecular attractive forces at a water surface, value being $0.0728\,N\,m^{-1}$ at $20^{\circ}C$.

Adhesion

The attractive force between water molecules and solid soil particles.

Cohesion

The strong intermolecular attractive forces between neighbouring water molecules.

Capillary binding

The mechanism of soil water retention caused by a combination of adhesive and cohesive forces in pores.

Capillary rise formula

The height ($h_{w}$) to which water rises in a tube: $h_{w} = \frac{2\sigma}{\rho_{w} g r}$.

Capillary fringe

The saturated soil layer immediately above the groundwater table maintained by capillary action.

Latent heat of vaporisation ($l$)

The energy required to break water molecule bonds for evaporation, approximately $2.45 \times 10^{6}\,J\,kg^{-1}$ at $20^{\circ}C$.

Evapotranspiration

The grouping of the identical physical processes of soil evaporation and plant transpiration.

Evaporative demand

Determined by energy supply and the removal of water vapour to maintain a pressure gradient; also called evaporativity.

Potential evaporation ($E_{p}$)

The maximum possible rate of evapotranspiration from a surface when water is continually supplied.

Actual evaporation ($E_{a}$)

The real rate of evaporation, which is less than or equal to $E_{p}$ unless additional energy is supplied by advection.

Advection

The transport of additional energy (e.g., from dryland to irrigated cropland) that can cause actual evaporation to exceed potential evaporation.

Energy-limited stage

The first stage of soil drying where evaporation is determined entirely by atmospheric demand ($E_{a} = E_{p}$).

Water-limited stage

The second stage of soil drying where evaporation rate decreases below the potential rate as water supply falls.

Matric forces

Forces that bind water to the solid soil matrix against drainage, evaporation, and root uptake.

Water release curve

The unique relationship for a soil between its moisture content ($\theta$) and its matric potential ($\psi_{m}$) or suction ($S$).

Hysteresis

The phenomenon where the water retention curve differs depending on whether the soil is wetting (absorption) or drying (desorption).

Saturated water content (\theta_{s})

The maximum moisture content in a soil when all pores are filled with water.

Air-entry value

The specific suction required to empty the largest soil pores so that air can enter the matrix.

Permanent wilting point (PWP)

The soil moisture content at a suction of about $1500\,kPa$, where plants wilt beyond overnight recovery.

Field capacity (FC)

The water content of a soil profile 2-3 days after heavy wetting when internal drainage has become very slow.

Transmission pores

Soil pores with diameters greater than $50-100\,\mu m$ that empty quickly after wetting.

Storage pores

Soil pores with diameters between $2-50\,\mu m$ that hold water available for plant transpiration.

Available water capacity

The amount of soil water available for plants, generally expressed as the difference between moisture at FC and PWP.

Total available water (TAW)

The available water capacity multiplied by the thickness of the crop's root zone.

Readily available water (RAW)

The portion of TAW that a crop can extract without exhibiting water stress.

Water stress coefficient (\beta)

A dimensionless reduction factor ranging from 0 to 1 used in models to adjust transpiration for water stress.

Root zone depletion ($D_{r}$)

The total water content in the root zone relative to field capacity where $D_{r} = 0$ at field capacity.

Management allowed depletion (MAD)

The fraction of total available water (TAW) that is permitted to be removed from the root zone before irrigation starts.

Relative daily transpiration rate ($RT$)

The ratio of the water flux of a plant on drying soil to a plant on well-watered soil.

Fraction of transpirable soil water (FTSW)

The ratio calculated as $(\theta - \theta_{l}) / (\theta_{u} - \theta_{l})$ representing soil water availability for support of plant transpiration.

Hydraulic potential (\psi_{h})

The sum of the gravitational potential ($\psi_{g}$) and the matric potential ($\psi_{m}$).

Gravitational potential (\psi_{g})

The component of hydraulic potential caused by elevation, typically taken as zero at the soil surface.

Matric potential (\psi_{m})

The component of hydraulic potential representing the negative pressure caused by matrix forces in unsaturated soil.

Pressure potential (\psi_{p})

The positive soil water pressure occurring below the groundwater table.

Darcy's law

The equation stating that soil water flow rate ($F_{w}$) is proportional to the hydraulic conductivity and the hydraulic potential gradient.

Tortuosity (\tau)

The measure of the convolutedness of the path that water must follow through soil pores.

Poiseuille’s law

The physical principle stating that the discharge rate ($Q$) through a pore is proportional to the fourth power of the radius ($r^{4}$).

Viscosity (\eta)

The internal friction of water that increases as temperature decreases, affecting hydraulic conductivity.

Preferential flow

The phenomenon where water and solutes bypass large volume fractions of the soil matrix through specific pathways.

Macropores

Non-capillary pores that allow for rapid preferential flow of water through the soil.

Interaggregate pores

Pores located between soil aggregates that are a common site of preferential flow.

Fingering

A type of preferential flow occurring at the interface where a less permeable layer sits above a more permeable one.

Soil water repellency

A condition caused by temporal dynamics or spatial irregularities that causes water to bypass regions of the root profile.

Pedotransfer functions

Mathematical equations used to calculate soil hydraulic parameters from more easily measured data like sand, silt, and clay content.

Van Genuchten equations

Mathematical expressions used to fit water retention and hydraulic conductivity data with high accuracy.

Stomatal conductance ($g_{s}$)

The measure of the rate of passage of $CO_{2}$ entering or water vapour exiting through the leaf stomata.

Water use efficiency (WUE)

An indicator of plant performance traditionally defined either agronomically or eco-physiologically.

Transpiration efficiency

Yield per unit area divided by water lost solely through the process of transpiration.

Abscisic acid (ABA)

A plant hormone produced in roots under water stress that signals the shoot to mediate stomatal closure.

Leaf water potential (\psi_{l})

State defined as $\psi_{l} = \psi_{o} + \psi_{p} + \psi_{g}$, expressing the thermodynamic status of water in leaves.

Osmotic potential (\psi_{o})

The negative potential component caused by the concentration of dissolved solutes in water.

Turgor

The positive hydrostatic pressure ($\psi_{p}$) within plant tissue cells.

Isohydric plants

Plant species, such as maize, that maintain a relatively stable leaf water status via strong endogenous control.

Anisohydric plants

Plant species, such as sunflower, that allow leaf water status to fluctuate with evaporative demand and soil water supply.

Stem diameter variations (SDV)

Diurnal changes in the trunk or stem size of woody plants driven by xylem water potential fluctuations.

Maximum daily shrinkage (MDS)

A specific stress index derived from continuous records of stem diameter variations.

Stem growth rate (SGR)

A plant performance index calculated from the diurnal records of changes in stem diameter.

Sap flow (SF)

The mass flow of water through the plant's transpiration stream, measured using heat as a tracer.

Transpiration ratio

The actual daily water use measured with SF sensors divided by the potential daily water use of well-watered plants.

Crop water stress index (CWSI)

A thermal stress index based on the difference between canopy temperature ($T_{c}$) and air temperature ($T_{a}$).

Physiological reflectance index (PRI)

A remotely sensed indicator sensitive to xanthophyll pigment changes under water stress conditions.

Solar-induced chlorophyll fluorescence

A physiological emission indicator used for remote detection of plant stress via steady-state chlorophyll fluorescence.

Gravimetric method

The direct field method for determining soil moisture by weighing a sample before and after oven-drying at $105^{\circ}C$.

Volumetric soil water content (\theta)

The ratio of the volume of water in a soil sample to the total soil bulk volume.

Neutron moderation

A technique using radioactive sources to detect thermalized fast neutrons to measure soil water content.

Dielectric permittivity (\epsilon)

A property of soil bulk used by sensors to estimate water content due to the high permittivity of water relative to soil solids and air.

Time domain reflectometry (TDR)

An electromagnetic method for estimating water content based on the travel time of an EM signal along a transmission line.

Piezometer

A tube open at both ends installed in a soil profile to measure positive pressure potential at a specific depth below the water table.