LE2 Flashcards
One of the most variable characteristic of soil
Water content
The soil acts as a ___________________, making it available for plants as it is needed
reservoir for water
Soil water is part of what cycle?
Global hydrological cycle
What factors of soil does water affect?
- Soil formation
- Structure
- Stability and Erosion
Water causes soil particles to :
- Swell and shrink
- Adhere to each other
- Form structural aggregate
Water alters the soil profile by?
Dissolving and translocating minerals
What causes the decrease in soil fertility under extreme rainfall events?
Leaching
Four reasons why water is essential to plants
- It constitutes 85-95% of the plant’s protoplasm
- Essential for photosynthesis
- Solvent in which nutrients are carried to, into and throughout the plant
- Provides turgidity
Classifications of Soil Water
Five categories of water surrounding a clay or soil particle :
- Adsorbed water (hygroscopic water)
- Water at permanent wilting point
- Capillary water (water at field capacity)
- Gravitational water
- Chemically-combined water
It is held in the surface of the particle by powerful forces of electrical attraction and virtually in a solid state of very small thickness
Adsorbed water (hygroscopic water)
Thickness of adsorbed water
0.005um
It cannot be removed by oven drying at 110 degrees celsius
Adsorbed water
Water that can be removed by oven drying but not by air drying
Water at permanent wilting point
Water that is not so tightly held
Water at permanent wilting point
Water that is held by surface tension, generally removable by air drying
Capillary water
Water that is removable by drainage, can move in the voids between soil grains
Gravitational water
Water that is not of much use to the plants
Gravitational water
Water that is in the form of water of hydration within the crystal structure
Chemically-combined water
Water that is not generally removable by oven drying
Chemically-combined water
What are the qualitative descriptions of soil wetness?
- Maximum retentive capacity
- Field capacity
- Permanent Wilting Point
- Available water storage capacity
It is a qualitative description of soil wetness when all soil pores are filled with water and becomes saturated
Maximum retentive capacity
A qualitative description of soil wetness where its matric potential is close to zero and the volumetric water content is essentially the same as total porosity
Maximum retentive capacity
TRUE OR FALSE
In maximum retentive capacity, the soil will remain at maximum retentive capacity as long as water continues to infiltrate, because water held in the largest pores will percolate downward under the influence of gravitational forces
TRUE
A qualitative description of soil wetness wherein moisture content of the soil after gravity has removed all the water it can. Usually occurs 1-3 days after rain
Field capacity
Qualitative description of water wherein smaller pores remain full of water, many of the intermediate pores are partially filled and most of the large pores are nearly empty
Field capacity
How much suction force must plants exert to obtain water at field capacity?
1/3 bar
Qualitative description of water wherein it is the soil moisture percentage at which plants cannot obtain enough moisture to continue growing
Permanent Wilting Point
TRUE OR FALSE
At PWP, water is held -very loosely- by the mineral and particles of the soil
FALSE
very tightly
How much suction force do plants exert to obtain moisture at PWP?
15 bars
TRUE OR FALSE
Although not yet dead, plants below PWP cannot recover if water is provided
TRUE
Qualitative description of soil wetness wherein it is the amount of liquid water stored in the soil and subsequently released for use by the plants
Available Water Storage Capacity
A qualitative description of soil wetness which varies directly with the total amount of medium-sized pore spaces
Available Water Storage Capacity
TRUE OR FALSE
In AWSC, pore spaces wider than 10 micrometers drain water readily and pore spaces narrower than 0.2 micrometer release the retained water too slowly
TRUE
The formula of AWSC
AWSC = FC - PWP
What forces allow the water to move through the soil?
- Gravity
- Osmosis
- Capillarity
At 0-1/3 bar suction, water moves through soil due to gravity; this is called _______________
Saturated flow
At higher suction, water movement is called _____________
Unsaturated flow
Because of the surface tension between water particles, water flows through the ground unevenly called _____________
Gravity fingers
Factors controlling water flow in the soils
- Soil texture
- Soil structure
- Amount of organic matter
- Depth of soil to impervious layers such as hardpans or bedrock
- Amount of water already in the soil
- Soil temperature
TRUE OR FALSE
-Coarse-textured- soils with granular structure are most favorable to infiltration of water
FALSE
Fine-textured
Three Main Types of Forces which Contribute to the Energy State of Soil Water
- Gravitational Potential
- Osmotic Potential
- Matric Potential
A force where water has a positive energy and can flow out of the soil through the large pores
Gravitational potential
A point when cohesive forces are not large enough to hold onto the water
Gravitational potential
A force that is only significant when soils are saturated
Gravitational potential
It is the movement of water from regions of higher potential to regions of lower potential
Osmosis
Force where its potential is due to the attraction that salts have for water through the phenomenon of osmosis
Osmotic potential
Force that is attributable to the presence of solutes in the soil solution
Osmotic potential
TRUE OR FALSE
The greater the concentration of solutes, the lower the osmotic potential
TRUE
This energy is negative relative to free water
Osmotic potential
Force wherein water flows from the solution with the lower solute concentration into the solution with higher solute concentration
Osmotic potential
The potential energy of water attracted to soil solids
Matric potential
Force that is operational in unsaturated soil above the water table
Matric potential
TRUE OR FALSE
In a -saturated soil-, matric potential results from the capillarity and adhesion forces
FALSE
unsaturated soil
TRUE OR FALSE
Plants must overcome the energy of matric potential to extract water from the soil
TRUE
Tenacity with which soil holds water
Soil Moisture Tension
TRUE OR FALSE
As soil moisture tension increases, the amount of energy exerted by a plant to remove the water from the soil must also increase
TRUE
TRUE OR FALSE
Soil moisture tension is negative tension
TRUE
Two forces that allow water to move through the soil
- Gravitational forces
- Capillary forces
TRUE OR FALSE
Gravitational and capillary forces act simultaneously in soils
TRUE
Two attractions involved in capillary action
- Cohesion
- Adhesion
TRUE OR FALSE
Capillary forces are greater in -large- pores
FALSE
small pores
What enables plant roots to make use of water from the wetter portions of the soil profile particularly from a water table
Capillary movement
Methods to measure soil water content
- Hand-feel method
- Gravimetric method
- Electrical Resistance Blocks method
- Neutron scattering method
- Tensiometer method
Ability of the soil to stick to itself or to other objects and its ability to resist deformation and rupture
Soil consistency
TRUE OR FALSE
Soil consistency largely depends on soil minerals and water content
TRUE
Soil physical property which is used in predicting cultivation problems and the ability of the soil to support buildings and roads
Soil consistency
Three moisture conditions that soil consistency is measured at
- wet
- moist
- dry
The ability of the soil material to adhere to other objects
Stickiness
The ability of the soil material to change shape, but not volume, continuously under the influence of an applied stress and to retain the impressed shape on removal of the stress.
Plasticity
TRUE OR FALSE
Testing is done when the soil is saturated with water, as, for example, immediately after a good rainfall
TRUE