Soil Water Characteristics and Behavior Chapter 5 NR

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. § § 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 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 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 runoff 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 (150 cm 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. § 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. 2. 3. Flood - Surface Sprinkler 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. 2. 3. 4. 5. Hand Set Permanent Set Wheel Line Center Pivot Hose Drag

Drip - Types § § § 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.