ENST 200 Exam 2

Matric potential

Always negative. Portion of total water potential due to adsorbtion and capillarity.

vadose zone

aerated region between the soil surface and the permanent water table

shrinkage limit

water content at which a solid soil becomes crumbly

Osmotic potential

portion of total soil water potential due to the presence of solutes in the water. Adding fertilizer salts lowers this potential by restricting water's movement. Usually negative.

water potential components

Gravitational, Osmotic, and Matric potentials

adsorbtion

adhesion of a thin layer of molecules of a substance to a solid or liquid

bar to kPa conversion

1 bar = 100 kPa

albedo

sunlight reflection coefficient

prefix: hygro

moisture

soil water content

Gravimetric method, neutron scattering, electromagnetic methods, and capacitance methods are used to measure what?

Darcy's Law

Equation used to estimate quantity of water that flows through a given soil over a given time

P = ET (evapotranspiration) + SS (soil storage) + D (Discharge)

Water balance equation

Drawbacks of Artificial soil drainage

Loss of wildlife habitat and organic matter, more contaminant leaching and flooding.

Redoximorphic features

Soil properties associated with wetness that result from redox of iron and manganese compounds after water saturation and desaturation.

1. Has wetland hydrology or water regime (saturated for some portion of year)

2. Hydric soils

3. Hydrophytic plants

3 requirements to be a wetland

Microorganisms thrive in warm wet environments.

Plants have small range of temp, seeds even smaller

Affect of soil temp on biological processes

Negative Water Potential

The soil is dry. It is hard for roots to extract water. the lower this value is, the more tightly the soil holds the water

Positive Water potential

The soil is not only saturated but below the water table. Water from the water table is pushing down.

What does a water potential of 0 kPa mean for the soil?

All pores are filled with water (saturated) and pores will typically drain due to gravity. A soil with water potential close to 0 will be very wet.

Permanent wilting percentage

Soil is very dry, with water potential of about -1500 kPa. Water forms thin film around soil particles, can't be used by plants

Hydrostatic pressure

the force that fluid molecules exert on each other because of the Earth's gravitational pull.

least limiting water range

soil water contents high enough that the soil is not too hard for roots to penetrate and low enough that roots can get sufficient oxygen

plant available water

amount of water held between 10 and 1500 kPa tension

field capacity

the amount of water remaining in the upper horizon of a mulched but unvegetated soil 1 or 2 days after a soaking rain. amount of water left when gravitational drainage has nearly ceased. normally between 0 kPa and -50 kPa

native plant roots grow deepest in which climate and texture?

dry and sandy because the roots have to grow deeper to get water. In a fine clayey soil, roots wont have to grow deep because water will be held closer to the surface.

What is inversely proportional to the radius of a capillary pore?

Height of the rise of water above the water table.

how to calculate water percentage of a soil (mass basis)

weight of water / weight of dry soil

unsaturated flow

movement of water through a soil that isnt saturated

which greek letter is used for percentage water content?

Theta

How to calculate volumetric water content? (theta v)

mass water content (theta m) * bulk density (D b)

Which symbol is used for density?

D

A soil with bulk density 1.3 Mg/m^3 has what mass when dry?

1300 kg

water content (g) at Field capacity - water content (g) at wilting point (-1500 kPa). same as plant available water

How to calculate plant-available water-holding capacity?

What is a cause of a water front moving deeper into the soil?

water moving into soil with lower matric potential

preferential flow

non-uniform movement of water through soil because of macropores (cracks, biopores, etc)

why is it desirable to manage soils that have a high infiltration rate?

More water is available for plants to uptake

Which irrigation system is the most efficient for field water efficiency?

micro / drip irrigation, this is the one with the tube and the slits/holes in it and only goes where the plants are

Why would you need percolation tests run on different parts of a rural lot when planning to build a house there?

To determine where the septic tank drain field should be located

Where does water loss by transpiration leave from?

The plants' stomatas

What is a way to prevent contamination of groundwater when there are chemicals on the surface?

Tilling the soil before: destroys macropores so water flows over them as runoff

Tilling the soil after: chemicals are mixed into the soils and can be broken down by the soil as they soak in slowly

What principle best describes movement of water into a perforated drainage pipe?

Positive water potential in soil -> 0 water potential in pipe

aerenchyma tissue

tissue that allows plants to receive oxygen in water logged soil

At what percentage(low) does air in the soil become limiting to plant growth?

10% total volume of soil or 20% of pore space

Which gas is much more concentrated in soil than air?

CO2

Why do they fence off trees around construction sites?

To allow shallow feeder roots to obtain oxygen from the original soil. Preventing compaction is another benefit

What does a chroma less than 1 indicate?

aquic or perquic moisture regime / hydric soil

How does microbial activity change when soil temperature raises 10 degrees celsius?

doubles

Which nutrient depletes first in warm wet conditions?

Nitrates

Will the use of a black or clear plastic 'mulch' film result in the warmest temperature?

black will absorb more energy

Does a change in soil or air temperature have a greater impact on plant growth?

Soil temperature change

Why is bulk density normally less than particle density?

Both have grams of dry solids in numerator, only denominator is different. Bulk density includes volume of the pores and particle density does not.

weight (g) of dry soil solids / volume (cm^3) of solids AND pores

How to calculate bulk density?

weight (g) of dry soil solids / volume (cm^3) of ONLY soil (completely compacted, not including pore space)

How to calculate particle density?

Surface seal

When rain breaks down salts on the surface and disperses clay. Creates an impermeable layer on the surface and causes runoff. common in tropics

Soil consistence

Ability of a soil to resist rupture: like the soil ribboning. ex. sticky loose friable

plastic limit

water content at which a semi solid becomes malleable plastic mass

liquid limit

water content at which a malleable plastic mass becomes a viscous liquid

Liquid limit - Plastic limit

How to calculate plasticity index?

Vapor movement

type of water flow in soils. Move from wet warm low salinity to cool cold high salinity

Percolation

Downward movement of soil water through the soil

Infiltration

Process by which water enters the ground pores and becomes soil water

Soil Aeration (process)

Air in the soil is replaced by air in the atmosphere. poor aerated has more co2 and well aerated has similar air to atmosphere by surface

Hydrostatic / submergence potential

Differences in pressure that occur because of water table. Going below water table means positive pressure

hydraulic conductivity

ease at which a liquid flows through a solid (K)

water potential gradient

Water moves from high to low potential through this gradient. Could be anything that allows this to happen. Passes through gradient similar to osmosis and diffusion

Potential evapotranspiration (PET)

Rate at which water would evaporate and transpire off plants if water was maintained at an optimal level. To do equation: PET = 0.65(correction factor) * pan evaporation

perched water table

water table above actual water table because of an impermeable layer that traps water.

Water deficit

PET-ET

Field water use efficiency equation

water transpired by the crop / water applied to the field

Why does soil take in CO2 and emit O2?

microorganisms breathe in O2 and breathe out CO2, affecting the pressure

Eh scale

A measurement of an element's potential to be reduced

element reduction

reduces amount of free oxygens. tends to happen when waterlogged. Releases harmful chemicals like hydrogen sulfide, methane, and nitrous oxide. decreases ph (H+ ions released) and raises eh(free

element oxidation

raises ph(H+ combines with other things) and lowers eh(o2 reduced)

when soil is saturated, organisms use up all O2 within a day or two. When O2 disappears, soil organisms use up other things like iron. Eh lowered because electrons reduced. Ph raised because H+ ions released (becomes more basic)

role of microorganisms in redox

Tensiometer

Tool used to calculate water potential in soil

capillarity equation

h = 0.15 / r

Water potential

difference in energy levels between pure water and the water in a particular soil

volumetric water content

Volume of water within a given volume (often m^3) of soil

mass water content

Mass of water within a given mass (often kg) of soil

Gravimetric method

Used to measure soil water content. Soil sample is weighed, dried, and re-weighed.

wetting front

distinct boundary of wet soil as it percolates down into dry soil because of gravity and matric potential

Maximum retentive capacity

A soil reaches this point when all pores are filled with water and it's saturated

Hygroscopic coefficient

Water at the surface of soil is held extremely tight to avoid evaporation, unavailable to plants

Soil texture, organic matter, compaction, osmotic potential, soil depth/layering

Factors affecting water availability for plants

Residence time

Average amount of time water spends in a particular area (ex: oceans, glaciers, aquifers, etc)

Leaf Area Index (LAI)

Leaf area per unit of land area.

climatic conditions, plant cover, efficiency of plants/crop management, and length of growing season.

Determinants of water losses from soil surface

Laying mulch, conservation tillage, no-tillage, planting crops close together

Methods of reducing evaporation

Unconfined aquifer

This kind of aquifer is not covered and water can percolate directly into it

Perched water table

Formed when water accumulates above impermeable layer in the soil

Benefits of Artificial soil drainage

Soil has more bearing strength, less frost-heaving, more oxygen, less fungal disease, methane, nitrogen and salts

wetting/drying, freezing/thawing, microbial activity, root/animal activity, absorbed cations that form aggregates (clumps)

Processes that form soil structures (5)

- Spheroidal (granular and crumb)

- Platy

- Blocky (angular and subangular)

- Columnar

- Prismatic

Types of soil peds (5)

Proctor compaction test

Test to see at what water content will a soil achieve maximum density

Atterberg limits

The water contents at which soils transform between solid, plastic, and liquid states

Perc test

Determines percolation rate expressed in millimeters of water entering soil per hour.

O2, CO2, CH4, C2H6, N

Main gases in atmospheric and soil air (5)

hydrophytes

Plants adapted to saturated soil conditions

Freeze/thaw creates cracks, forms peds

Affect of soil temp on physical processes

Cool temps inhibit root functions, can cause nutrient deficiencies (especially phosphorous)

Affect of soil temp on chemical processes