Soil Science - Water

Front 1

Cohesion

Back 1

Attraction btwn like molecules.

Water = polar molecule. Electrons are shared unequally in a covalent bond between O and H atoms. O hogs the single H electron so it becomes slightly neg. The H atoms become slightly pos.

H ends water molecules are attracted to the O ends of other water molecules. (H bond)

Front 2

Adhesion

Back 2

Attraction btwn unlike molecules.

Surface of soil particles have slight negative charge, attracted the H end of water molecules.

Front 3

Ionic bonds (Cation/Anion)

Back 3

Attraction between oppositely charged ions.
Cation - Positive Charge. Has lost electron. (Cats have paws)
Anion - Negative Charge. Has gained electron (A-Negative charge)

Front 4

Explain how salt dissolves in water

Back 4

NaCl is joined by an ionic bond. Na=cation. Cl=anion.

O end of water molecule (-) attracts the cation Na.
H end attracts anion Cl.

Front 5

Oxidation and Reduction Reactions

Back 5

Shuffling of electrons - and electronmagnetic shift.

OIL RIG. Oxidation is Losing. Reduction is Gaining.

Oxidation = loss of electrons or H atoms. Usually to O, making you +.
Reduction = gain of electrons or H atoms, making your more -.

Front 6

H atom is made up of...

Back 6

1 proton and 1 electron. Often involved in chemical reactions.

Front 7

Soil-Water Potential

Back 7

Concept used to measure the ease with which water can move through a soil profile and be absorbed by plant roots.

0 bars to -1/3 bars = Gravitational Water
(Highest Potential)
-1/3 bars = Field Capacity
-15 bars = Permanent Wilting Point
-31 bars or more= Hydroscopic Point
(Lowest Potential)

Front 8

Water Potential of Zero?

Back 8

Theoretically freely flowing water in a pool.

Front 9

Soil Water Potential = ? + ? + ?

Back 9

Matric P + Osmotic/Solute P + Gravitational P.

Matric P: The attraction of water to soil particles. Always a negative value. The largest part of soil-water potential.

Osmotic/Solute P: A factor in soils of high salt content, either naturally or through over-fertilization. Measures bonds between salt ions and the water molecules, which make water unavailable to plants. Always negative.

Gravitational P: Soil is at saturation point and water drains within 24-48 hours b/c gravitational forces stronger than cohesion (or Hydrogen bonding) between water molecules. Highest soil-water potential at greater than -1/3 bars.

Front 10

Field Capacity

Back 10

Maximum amount of water held in soil after gravitational water flows through. Matric potential is balanced with gravitational potential. Ideal moisture level for plant growth b/c of balance btween air/water.

Front 11

Available Water (bars?)

Back 11

Cohesion water that can be absorbed by plants. (Not all cohesion water can be absorbed)Between field capacity and perm wilting pt.
- 1/3 bars to -15 bars.
In Sandy Loam, 25% of water at saturation is available.

Front 12

Permanent Wilting Point

Back 12

Only a small bit of cohesion water remains and it is unavailable to plants.

Front 13

Hygroscopic Water (bars?)

Back 13

Present when soil is air dry. This water can only be removed by heating in oven. -31 or more bars

Front 14

What is Matric Potential at Saturation?

Back 14

About zero.

Front 15

Perched Water Table

Back 15

A zone of saturated soil that is higher than the surrounding water table. Water cannot percolate through to water table.

Occurs when there is a sudden change in texture. (Course to fine, like clay) or with compaction beneath top soil.

Front 16

Tree Planting - Best Practice

Back 16

Dig hole only as deep as root ball but 2x width. Digging deeper to loosen soil beneath root ball may cause later sinking of plant as loosened soil settles.
2x width aids in water infiltration & percolation and aerates soil, stimulating new root growth away from root ball.
If soil is compacted, plant root ball on a pedestal to avoid creating a perched water table. Excess water can drain away into this underground "moat".

Front 17

Potential Problem with container grown trees in loose organic mix?

Back 17

When planted in denser and more finely textured ground soil, course medium around roots may not be able to retain water before plant establishes. Always better to have a clayier root ball than surrounding soil.

Front 18

Temporary Wilt

Back 18

Caused by sudden change in atmospheric temperature and/or humidity. Root update and water transport cannot keep up with quicker rate of evapotranspiration.

Front 19

Why is high sodium content in soil detrimental?

Back 19

1. Osmotic potential makes water unavailable to plants
2. Changes soil pH
3. Destroys soil structure

Front 20

Saturated flow

Back 20

Same as gravitational flow. Occurs only when soil is completely saturated

Front 21

Unsaturated flow

Back 21

Same as capillary flow. Usually sideways, but also up and down. Flow is from wetter to drier soil. Higher to lower potential. Depends up on a continuous unbroken film of water, uninterrupted by air bubbles. Flow rate depends on how steep the gradient is between wet and dry areas. Limited distance.
Finer textures - no more than 12"
Course textures - 1" (larger pores = greater amount of air to break film)

Front 22

Wetting front

Back 22

Water cannot move deeper into the soil until saturation occurs in top layers. Soil behind the wetting front is saturated. Soil beyond the wet front is dry. But what if the soil beyond wetting front is already moistened?

Front 23

Describe bonds between H and O in water molecules.

Back 23

Oxygen atom combines with 2 H atoms through a H bond. The 2 electrons from the H atoms are shared with the O, but b/c O is more electronegative, the O atom kind of hogs the electrons. This means that the H end of the molecule becomes slightly pos, and the O end slightly negative.
Also called Polar Covalent Bond.

Front 24

What do Oxygen atoms like to do and why?

Back 24

Steal electrons, b/c their outer shell is incomplete with just 6 electrons. Wants 2 more for stable shell of 8.

Front 25

What is most common element in soil?

Back 25

Oxygen

Front 26

BOD/COD

Back 26

Biological/Chemical Oxygen Demand
Substances in water that use up the dissolved oxygen. Plants vary in their sensitivity. Higher incidence in summer w/ high temps.
Bio: decaying organic matter Chem: Fertilizer residue

Front 27

Turbidity (management of?)

Back 27

Amount of suspended sediment in water
-Filter
-Holding area for settling

Front 28

5 Factors governing the frequency and volume of overhead watering

Back 28

1. Depth and distribution of plant roots
2. Water retention capability of soil in root zone
3. Minimum water potential required by plant type (i.e. Tropical vs. Desert)
4. Rater of water use by plants (i.e. Large dark foliage vs. small light foliage or size and health of plant)
5. Availability of water supply

Front 29

What factors affect water retention in soil?

Back 29

Primary: Texture
Other: Structure, organic content, density, depth.

Front 30

Worst time to ration water?

Back 30

When setting bud, flower, or fruit.

Front 31

What elements negate effects of sodium in soil?
What do you treat sodic soils with?

Back 31

Calcium and Magnesium (Ca + Mg)
Treat with gypsum (high in Ca)

Front 32

TSS? How measured?

Back 32

Total Soluble Salts. B/c ions conduct electricity, you can use EC meter to measure the amount of ions (salts) in the water.

Front 33

Water quality is more important in which setting?
Outdoor or Indoor horticulture?

Back 33

Indoor, b/c irrigation depends solely upon ground water. No rainwater.

Front 34

4 Drainage Issues

Back 34

1. Uniformly high water table
2. Underlying bedrock
3. Underlying soil pan
4. Excess accumulation of surface water

Front 35

4 Drainage Issues & Management Techniques

Back 35

1. Uniformly high water table
- Plant in raised beds or create berms & swales
- Dig drainage pond

2. Underlying bedrock, esp with concave areas
- Contour land to create runoff away from problem areas

3. Underlying soil pan creates perched water table
- Create little drainage holes over problem area by digging through pan. Fill with pipe and prevent clogging with gravel, landscape fabric, etc...

4. Excess accumulation of surface water due to low spot.
-Fill in low area (being careful not to just displace water into another low area)
-Curtain drain

Front 36

3 Types of Water Erosion

Back 36

1. raindrop splash under eaves, air conditioners or in areas abutting hardscape.
2. Surface Flow/Sheet: uniform washing away of thin layer
2. Channelized Flow: Starts with wee rills (easily fixed) which increase in size and eventually form gullies which are more difficult to fix.

Front 37

Tolerable Soil Loss

Back 37

Amount of soil loss that can be tolerated. (T)

Front 38

What is equation used to calculate soil loss per acre/year?

Back 38

A = R K LS C P
A: Tons of soil lost per acre/per year
R: Rainfall amount and intensity (erosive power)
K: Soil erodibility factor
LS: Length and gradient of slope
C: Type and density of vegetative cover
P: Management Practices

Front 39

Soil erodibility factor? Easiest way to improve?

Back 39

How easily does soil in a particular area erode? Based on soil type:
Texture: Fine sand & silt are most erodible
Structure: Peds stabilize particles
Organic matter content: Improves water absorption and retention, reduces runoff

Easiest way to improve? Add organic matter

Least erodible .01 -- Most 1.0

Front 40

What type of planting is best for reducing erosion?

Back 40

Dense sod. Has intensive root system and thick foliage which covers soil surface well.

Front 41

Which has greater velocity at base of slope - convex slope or concave slope?

Back 41

Convex has greater velocity

Front 42

Urban water erosion aggravated by what 3 factors?

Back 42

1. Impermeable surfaces
2. Lower organic matter content of soil
3. Perched water tables

Front 43

What 5 practices can limit erosion on construction sites?

Back 43

1. Strip less vegetation, or strip sections in stages as needed
2. Divert Runoff using drains or obstructions
3. Retain sediment & slow water flow with silt fences or hay bales
4. Retention ponds and/or sediment basins
5. Mulch