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

 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 Uses

Water Molecule structure  Structure  Two hydrogen atoms one oxygen atom  this attachment is held at 105   this hydrogen side is positively charged

 Creating a polar molecule  Causing it to be attracted strongly to itself, cohesion  Also attraction towards other material, adhesion.  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 Water Molecule Structure

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

 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 Water movement and retention

 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  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  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  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?  A. Climate  B. Type of crop  C. Cost of water (availability)  D. Slope of field  E. Physical properties of soil  F. Drainage capability  G. 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  1. Hand Set  2. Permanent Set  3. Wheel Line  4. Center Pivot  5. Hose Drag

Drip - Types  1. Micro Emitters  2. In-Line Emitters  3. Adjustable Emitters  4. Drip Tape  5. 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.