Carly Nigg
Chapter 5 Summary
Important Terms
Adhesion is a force holding together the surfaces
of two substances due to molecular attraction.
Capillary water is the water held in the small
pores of soils.
Cohesion is a force which holds either a solid or a
liquid together due to like molecules attracting to
each other.
Gravitational potential is the total soil water
potential due to differences in elevation of pure
water and of soil water.
Hydrogen bonding is a low energy from a
hydrogen atom between two electronegative atoms
(in this case oxygen).
Mass flow is the movement of nutrients with water
to plant roots.
Osmotic potential is the total portion of soil water
potential directly from the presence of solutes on
soil water.
Soil water potential is the difference the free
energy state of soil water to pure water.
Surface tension is an attractive property of liquid
molecules and between liquid and gas molecules at
the liquid-gas interface.
Wetting front is the boundary between a wet soil
and a dry soil during infiltration.
Saturated flow takes place when the soil pores are
completely full.
Vapor movement occurs when vapour pressure
differences arise in dry soils.
Unsaturated flow happens when the large pores
are filled with air leaving the small pores to hold
and transmit water.
Figure 5.5(c): Water movement by capillary
100
Capillary rise (cm)
80
60
Sand
Loamy Sand
40
Clay Loam
20
0
0
2
Time 4(days)
6
8
Summary
-The water molecule has a polar structure that
results in electrostatic attraction of water to both
soluble cations and soil solids.
-The forces of adhesion and cohesion of water
molecules make it possible for the soil solids to
retain water and control its movement and use.
-Capillary movement is determined by pore size
that largely determines the amount and rate of
movement of capillary water in the soil
-There are 3 major forces acting on water: matric
force (reduces energy state of water near particle
surfaces), osmotic (tends to reduce the energy state
of water in soil solution), and gravity (pulls water
downward).
-Gravity plays an important role in removing
excess water from upper horizons and in
recharging groundwater below the soil profile.
-Three types of water movement within the soil
are: (1) saturated flow, (2) unsaturated flow, and
(3) vapour movement
-water is supplied to plants by capillary movement
towards the root surfaces
-Vapor movement may be important by supplying
water for drought-resistant desert species.
-Osmotic potential is important in soils with high
soluble salt levels that can impede plant uptake of
water from the soil.
Figure 5.5(c) shows upward capillary movement of
water through tubes of different bore and soils with
different pore sizes. Here the finer the soil texture,
the greater the proportion of small-sized, and
hence, the higher the ultimate rise of water above a
free-water table. However, because of the much
greater frictional forces in the smaller pores, the
capillary rise is much slower in the fine-textured
soil than the sand.
Figure 5.5(c): Water movement by capillary
100
Capillary rise (cm)
80
60
Sand
Loamy Sand
40
Clay Loam
20
0
0
2
Time 4(days)
6
8