Transcript Soil Water: Characteristics and Behavior

Soil Water:
Characteristics
and Behavior
Chapter 5 – NR 200
Water Uses
 How the plant uses water.
 60-90% of plant mass is water
 When a plant has a full complement of water it is
said to be turgid, loss of turgidity results in wilting.
 Is essential for cell functions
 Photosynthesis
 Transpiration helps cool the leaf
 Plant nutrients are in solution
 Carries carbohydrates in phloem
Water Uses
 Improper amount of water
 Stress – too little
 Wilting
 Permanent wilting point
 Water stress weakens plant
 Too much water
 No air space
 Anaerobic conditions exist when no oxygen
available
Water Molecule structure
 Structure
 Two hydrogen atoms one oxygen atom
 this attachment is held at 105
 this hydrogen side is positively charged
Water Molecule Structure
 Creating a polar molecule
 Causing it to be attracted strongly to itself,
cohesion
 Also attraction towards other material, adhesion.
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The force that attracts water to other objects
In small spaces this force can move water
In large spaces the affect is minimal
Responsible for the surface tension of water
Water Molecule Structure
 Capillary water
 The ability of water to move upward against
gravity or outward.
 This ability is directly related to adhesion and
cohesion
 The meniscus is pulled up a small tube by
adhesion properties of the tube and the cohesion
pulls the other water molecules with it. The
height of travel is related to the size of the tube.
h = .15/r with the radius in cm
Soil Water Energy forms:
The energy that acts on soil water
 Matric force is the soil solid’s attraction
(adhesion) to water which causes
adsorption and movement of water
through the soil (capillarity) not counting
the force of gravity.
 Osmotic force is the movement of a
high concentration of ions to a lower
concentration.
 Gravity
Water movement and
retention
 Movement
 Texture and the wetting pattern
 Clay soils produce a more round ball pattern
 Sandy soils produce a more oblong pattern;
water percolates more quickly into the soil
Water movement and
retention
 Types of water movement
 Gravitational Water or Saturated flow
 Water that moves through the root zone and
below
 Water movement varies as to the soil texture
 Water movement in the soil changes when water
moves from one different/unmixed texture soil to
another
Water movement and
retention
 Types of water movement (cont’d)
 Capillary movement
 Small pores water moving laterally
 Conditional on texture and structure
 Large pores
 Little water retention
 Sand
 Small pores
 Great water retention
 Clay
 Types of water movement (cont’d)
 Capillary movement (Cont’d)
 Medium pores
 Fine sand and silt hold the most available water
 Infiltration - the process in which water moves
into the Soil
 Percolation is the downward movement of water
through
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the soil
soil texture
Compaction
Soil stratifications affect the soil how?
Water soil terms of
wetness
 Maximum retentive capacity
 Water has filled all pore spaces
 Can only be maintained by more water or no
percolation
 Field Capacity
 After gravitational water has moved out and
the soil is holding the water
 Sometimes called capillary water
Water soil terms of
wetness
 Permanent Wilting Point (PWP) or wilting
coefficient.
 That point of no return for a plant wilting
 Water in the soil is no longer available to the plant
 Available water is the difference between Field
capacity and PWP
 A fine sand or silt loam will have the highest available
water
 Hygroscopic water - water held so tightly it is
unavailable to the plant
Water removal by the
plant
 Removal of water from the surface area
first then the lower areas
 Water around the soil particle is removed
by the root hair and used by the plant.
 The root must be in contact with the soil
to remove its water.
Measuring soil water
 Gravimetric Measurements
 Weight difference between soil and oven
dried soil = percentage of weight of the
water.
 Tensiometers
 Measures the moisture pull of the soil in a
tube or the measures the water potential of
the soil
Tensiometers
Measuring soil water
 Electrical Resistance block
 Measures the conductivity through a block of
gypsum or other buffering material. More
water the less resistance. This device can
easily be hooked to a watering device to
automatically water a given field.
Electrical Resistance
block
Time Domain
Reflectometry
 May be automated
 Requires wave guides
 Expensive instrument
Time Domain
Reflectometry
Neutron Scattering Probe
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Radiation permit required
Expensive equipment
Requires access tube
Not good in high-organic soils
Neutron Scattering Probe
How does water move
around on this planet?
 97% of our world’s water is in the ocean
 our ground water only makes up another
.7%
 of the .05% of the other water, 60% is in
lakes and 33% trapped in the soil
How does water move
around on this planet?
 Most of the clouds are therefore formed form
the oceans by evaporation and transpiration
together these two avenues of water into the
atmosphere are called evapotranspiration (ET).
 This rain then falls on areas we call watersheds
usually defined as river area bounded by mountains
or hills that divide the waters movement from one
another.
 We utilize the Tuolumne River watershed with Don
Pedro the primary storage site with Modesto and
Turlock reservoirs the secondary storage site.
How does water move
around on this planet?
 Reducing ET and Evaporation
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Remove unwanted vegetation
Fallow periods for water replenishing
Vegetative mulches and crop residues
Plastic mulches
??
How does water move
around on this planet?
 Water infiltration and percolation
 If water does not move into the soil, then
run-off occurs
 Water that is in the soil moves downward
into least water potential area.
 If the downward movement is impeded then the
water backs up until it forms a lake or moves into
another lower area.
 Drainage can reclaim high water saturated areas
 Surface draining – Ditches and slope
 Sub-surface -
Drainage
 What do we do with
our tail water?
 What is the problem
with tail water?
How does water move
around on this planet?
 Water infiltration and percolation (cont’d)
 Water and the dissolved elements move with the
water to lowest area
 Applications for septic tanks
 Enough percolation to have water move into the soil
 But not too fast as the soil cannot filter out the solids
(150cm per hour)
How does water move
around on this planet?
 Irrigation methods
 Water is getting scarcer and more people
want it we must use the present water in a
more efficient manner.
Irrigation
 1. How do we measure water?
 2. How do we decide what method to
use?
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A.
B.
C.
D.
E.
F.
G.
Climate
Type of crop
Cost of water (availability)
Slope of field
Physical properties of soil
Drainage capability
Salinity or other problems
Irrigation
 1. Flood - Surface
 2. Sprinkler
 3. Drip - Microirrigation
Flood - Types
 1. Checks
 2. Furrow
A. Plastic or Alum. Pipes
B. Gated Pipe
C. Poly Pipe
D. Permanent pipe (valves)
Sprinkler - Types
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1.
2.
3.
4.
5.
Hand Set
Permanent Set
Wheel Line
Center Pivot
Hose Drag
Drip - Types
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1.
2.
3.
4.
5.
Micro Emitters
In-Line Emitters
Adjustable Emitters
Drip Tape
Many more types
Soil Moisture Behavior
 1. Saturation (1/10 Atmosphere)
 2. Field Moisture Capacity (1/3
Atmosphere) ½ saturation
 3. Permanent Wilting Percentage (15
Atmosphere) ¼ saturation
How does water enter the
soil?
 through pores in the soil
 sandy soils have the largest pores, but are
often filled with other material
 medium textured soils (loamy) have good
water entry properties
 clays, pores swell shut when they get wet
How does water move
around on this planet?
 Use of water for management of high salt
soils
 Perhaps improved drainage to remove
excess water
 Use more water to leach out the salts as
long as there is a good clean source of
water is available.
Salt movement in soil.
Salt movement in soil.