Chapter 6 Soil water Flashcards
When dry soil is crushed in the hand, it can be seen that it is composed of
all kinds of particles of different sizes.
When dry soil is crushed in the hand, it can be seen that it is composed of all kinds of particles of different sizes.
Most of these particles originate from
degradation of rocks; they are called mineral particles.
Some originate from residues of plants or animals (rotting leaves, pieces of bone, etc.), these are called organic particles (or organic matter).
The soil particles seem to touch each other, but in reality have
spaces in between.
The soil particles seem to touch each other, but in reality have spaces in between. These spaces are called
pores
When the soil is “dry”, the pores are mainly filled with
air
After……………………………………….., the pores are mainly filled with water
irrigation or rainfall
Living material is found in the soil. It can be …………………………………………………………..
live roots as well as beetles, worms, larvae etc.
living materials help to…………………….. and thus……………………………………………..
aerate the soil and thus create favourable growing conditions for the plant roots
The following image represents
The composition of the soil
A represents
Soil Particles
B represents
water
C represents
air
D represents
root
If a pit is dug in the soil,………………………………………………………………………….. can be seen.
- At least 1 m deep,
- Various layers,
- Different in colour and composition
If a pit is dug in the soil, at least 1 m deep, various layers, different in colour and composition can be seen. These layers are called
horizons
the profile of the soil:
succession of horizons
soil profile:
- The plough layer
- The deep plough layer
- The subsoil layer
- The parent rock layer
The following image represent the
Soil profile
A represent
Plough layer
B represents
Deep plough layer
C represents
Subsoil layer
D represents
The parent rock layer
Name of the particles:
gravel
Size limits in mm:
larger than 1
Name of the particles
gravel
distinguishable with the naked eye:
Obviously
Name of the particles:
sand
size limit in mm:
1 to 0.5
Name of the particles:
sand
Distinguishable with naked eye:
easily
Name of the particles:
silt
Size limits in mm:
0.5 to 0.002
Name of the particles:
silt
Distinguishable with naked eye
barely
Name of the particles:
clay
Size limits in mm:
less than 0.002
Name of the particles:
clay
Distinguishable with the naked eye:
impossible
………………………………..determines the soil texture.
The amount of sand,
silt and
clay present in the soil
In ……………………….textured soils: ………………………… is predominant (sandy soils).
coarse
sand
In ……………………. textured soils: ……………….is predominant (loamy soils).
medium
silt
In …………………..textured soils: …………………..is predominant (clayey soils).
fine
clay
In the field, soil texture can be determined by
rubbing the soil between the fingers
Soil structure refers to
or soil structure refers to
the grouping of soil particles (sand, silt, clay, organic matter and fertilizers) into porous compounds. These are called aggregates
or
Soil structure also refers to the arrangement of these aggregates separated by pores and cracks
When present in the topsoil, a massive structure
blocks the entrance of water
When present in the topsoil, a massive structure blocks the entrance of water; seed germination is difficult due to
poor aeration
if the topsoil is ………………………………., the water enters easily and the seed germination is better
granular
The following soil structure is
Grangular
The following soil structure is
Blocky
The following soil structure is
Prismatic
The following soil structure is
Massive
In Granular soil structure the flow is ……………………..
rapid
In Blocky soil structure the flow is ……………………..
moderate
In Prismatic soil structure the flow is ……………………..
moderate
In Massive soil structure the flow is ……………………..
Slow
The depth of the ……………………………………varies greatly from place to place, mainly due to changes in ………………………………..
groundwater table
topography of the area
In one particular place or field, the depth of the groundwater table may vary in …………
time
A perched groundwater layer can be found
on top of an impermeable layer rather close to the surface (20 to 100 cm)
A perched groundwater layer can be found on top of an impermeable layer rather close to the surface (20 to 100 cm). It covers usually a …………………..area.
limited
The top of the perched water layer is called the
perched groundwater table
A represents
Soil surface
B represents
Perched water layer
C represents
Compacted layer
D represents
ground water table
Infiltration:
The movement of water from the soil surface into the soil
Redistribution:
The subsequent movement of infiltrated water in the unsaturated zone of a soil.
Redistribution involve:
- Exfiltration
- Capillary rise
- Recharge
- Interflow
exfiltration
evaporation from the upper layer of the soil
capillary rise
movement upward from the saturated zone to the unsaturated zone due to surface tension
recharge
movement of water from the unsaturated zone to the saturated zone
interflow
flow that moves downslope
Infiltration and redistribution depend critically on……………………………………………….
the material and hydraulic properties of soils
The groundwater can be sucked …………………………by the soil through …………………………….. that are called …………………………
upward
very small pores that are called capillars .
The groundwater can be sucked upward by the soil through very small pores that are called capillars. This process is called ……………………..
capillary rise
Soil texture:
Coarse (sans)
Capillary rise (in cm):
20 to 50 cm
Soil texture:
medium
Capillary rise(in cm):
50 to 80 cm
Soil texture:
fine (clay)
Capillary rise (in cm):
more than 80 cm up to several meters
Darcy’s Law states that the flow rate in the horizontal depends on
(1) the ability of the soil to “conduct” water;
(2) the magnitude and direction of the slope, which is the gravitational potential energy gradient per unit weight of flowing water (soil water wants to flow downhill, towards lower gravitational potential energy), and
(3) the magnitude and direction of the horizontal gradient in soil water pressure (if soil water pressure decreases in the x direction, the water wants to flow in that direction).
hydraulic conductivity
the vertical flow rate depends on the sum of the gravitational potential energy gradient per unit weight of water (dz/dz =1) and the vertical gradient in soil water pressure.
In a steady state (qz equals ……………)
zero
there is a balance between …………………………… and ………………………………
the effect of gravity
an upward decrease in soil water pressure
the effect of gravity (which always wants to …………………………………of ………………………………, .towards……………)
pull the water “down the gradient”
gravitational potential energy
lower z
an upward decrease in soil water pressure (“…………….. the gradient” is in the …………………….. z direction).
down
positive
if the effect of gravity and an upward decrease in soil water pressure don’t balance there is
a vertical water flow (up or down, depending on which term “wins”), the magnitude of which depends of the size of the imbalance and the value of the hydraulic conductivity coefficient.
