Chapter 4: Soil Water Properties Flashcards
Molecules like little magnets, have generally “+” and “-“ charged sides.
Polar
Molecules stick slightly to each other
Cohesion
Molecules stick to other charged molecules.
Adhesion
Forces holding or moving water in the soil.
Soil Water Potential
Water held to soil particles by hydrogen bonds.
Matric Potential
Water held to dissolved salts in soil solution.
Solute Potential
Gravity “pulling” water through the soil.
Gravitational Potential
Water that drains “freely” from soil, usually about 3 days after irrigation.
Gravitational Water
Amount of water (usually inches per foot of soil) held by soil after gravitational water drains off.
Field Capacity
Amount of water held in soil when plants are permanently damaged from water stress.
Permanent Wilting Point
Amount of water held in soil between field capacity and permanent wilting point.
Available Water Capacity
Many soils in __________ County are affected by salt.
Kern
The more negative the charge, the ____________ the bond.
Stronger
Clay is a “sponge” because of ____________.
Oxygen
Solute Potential is generally a ________ thing.
Bad
Solute Potential is very important to _________________.
Agriculture
All ________ __________ have a lot of oxygen radicals sticking out.
Living Things
Most crops can remove __________ of the water (on average).
Half
Soil is __________ charged, so it sticks to water.
Negative
Water is ____________ charged.
Positive
High heat Capacity can ___________ crop production.
Extend
Ice has a lot of _______ in it that insulates and protects lakes and other bodies of water.
Air
Hydrogen parts of water __________ to soil.
Attach
Sand has _______ negative charge.
Low
Silt has a higher ____________ charge.
Negative
Clay has a ________ negative charge.
High
Field Capacity in an “average” AG soil = ______ Water of saturated soil.
1/2
Available Water Capacity in an “average” AG soil = _____ field capacity.
1/2
__________ ___________ have low field capacities, but may have moderate available Water holding capacity, because all water that is left after drainage is available.
Sandy soils
__________ have highest field capacity, but low available water capacity, because waster held very tightly to clay particles.
Clays
Best all around soil is the _________ soils with high field capacity and high available Water Capacity.
Loamy
Weigh, dry, weigh again
- slow, labor intensive
- Good for lab samples that must be dried anyway
Gravimetric
Air pressure pushes water out of soil
- Pressure needed related to water content
- Good for quick results in lab
Pressure Bomb
2 electrodes, 1 cm apart, inside porous block. Conductivity related to water content of block; more water = more conductance.
- Blocks can be buried in soil
- Relatively cheap and fast and reliable
- Inaccurate in salty soils
Porous Blocks
Method where you will squeeze the soils with your hand to see if water drips from it or if it forms a ball. You can also roll the soil and see if it falls apart.
Soil feel method
Device put down hole that emits fast neutrons. Neutrons that hit water are reflected, returned and are measured.
- Proportion of slow to fast related to water content
- Immediate results and 100% accurate
- radioactive
- you need to be licensed to do this method
Neutron Probe
Water reflects radio waves (radar), much more that soil particles
- Proportion of received to emitted waves estimates soil water
- Very expensive equipment
- Certain wave frequencies will penetrate the soil, and the frequency coming back will indicate the water content.
Radio Waves
Tubes filled with water with a porous cup on the end. As water pulled out into dry soil from cup, water level in tube drops and measured by suction on meter
- Relatively cheap
- Not very accurate in dry soils
Tensiometers
Moves by the force of gravity
- Before the three days are over
- Starts with infiltration and can end with deep percolation
“Free” or Saturated Flow
___________ textured soils have much more saturated flow than ___________ textured soils.
Coarser; Finer
_________ _________ increases saturated flow by keeping soil pores open.
Organic Matter
Flow in soil pores from field capacity to permanent wilting point
Unsaturated Flow
Unsaturated flow will flow from wetter to drier areas and can flow against gravity to bring up _________.
Salts
