WATER

Nutrients are dissolved in water H₂O

Properties of Water

1. 90% of Weight of Plant
2. Wonderful Solvent
3. Reactant or Product of Reactions
4. High Specific Heat
5. Evaporative Cooling

Where do plants get their water?

1. Precipitation = Rain, snow, sleet, hail
2. Run-off = Streams, rivers
3. Water table = Ponds, lakes
4. Soil water
5. Aquifers and springs

Horizon A = leached topsoil
Horizon B = accumulated subsoil

Erosion fits in here somewhere!

			Friable!
Mud	-------->	Field Capacity	-------->	Wilting Point	-------->	Dry!
	| V Gravitational Water (erosion!)		| V Capillary Water (used by plants)		| V Hygroscopic Water (unavailable)

Clay = high water capacity, high hygroscopic

Sand = low water capacity, low hygroscopic

Irrigation = keeping soil friable!

1. Natural-hope for 4" of rain each month...weather report
2. Sprinkler-washes off mites, insects, dust

+kills "eggs" of many "bugs"
+may apply fertilizer/insecticide at same time
-WASTES WATER
-WATER DROPS ON LEAVES = DEAD SPOTS
-HUMIDITY + = FUNGI +
Moveable vs Stationary

3. Surface-reduces fungi but raises salts to upper soil

Furrow irrigation = between rows in crops
Flood irrigation = perimeter furrows, ground level, no runoff-laser guided earth graders

4. Trickle Irrigation

-less water/fertilizer/pesticide used
-no pulse of these

5. Wick Irrigation -pots on wet mats (overload) or wicks

To keep it friable (between field cap. and wilting point)
Not like people: 3-squares with 8 glasses
Green Thumb? Dirty Finger!
Meters unreliable!
House Plants:

Soak to Field Capacity
let dry to wilting point
soak again, etc.

Early AM so it evaporates before sun hot
NEVER evening, warm but cooling leads to FUNGI

*Too dry? Hydrophobic, water runs off = flash floods

*Friable ideal

*Too wet? Air excluded from space in soil = anaerobic so plants die!

What to do?
Pots with holes
Perlite in mix
Tile fields

Less Frequent but DEEPER irrigation beneficial

Preserve Water by:

Mulch = plastic, stone, paper, leaves, straw (-evap)
Weeding = controlled spacing (-competition)
Terrarium for plant storage for vacations (Plastic bag)

Symptoms of watering trouble:

Excess moisture:

Root Death because of no air in soil
Fungi Thive (Damping Off of seedlings)
Cracking (Cabbage, Fruits, Roots)
If roots die, plants WILT!

Deficient moisture:

Growth inhibition - Abscisic Acid Produced
Brown tips
Abscission of Leaves -Ethylene Produced
Plants WILT!

BROWN FINGERS not GREEN THUMB!
Most people kill by overwatering!

Osmosis explains this:

Movement of Water from purer water toward saltier water

Isotonic = No net change (no growth possible)

Hypertonic = Water leaves, Turgor lost, Wilts

Celery wilted in refrigerator...what to do?

Hydroponics = water culture without soil

nutrients, aeration, support are major problems!
1/10 strength + Perlite

Why water?

1. Photosynthesis (CO₂ + H₂O --- light ---> CH₂O + O₂)
2. Prevent Wilting (permit growth)
3. Disolve Minerals in Soil
4. Transpiration - soil>root>stem>leaf>atmosphere in XYLEM
5. Translocation - leaf>stem>flower>fruit>apical bud
leaf>stem>root
in PHLOEM
6. Evaporative Cooling - leaf>atmosphere

Factors Affecting How Much Water is Needed

1. Stage of Growth

Seedling = low but EVEN
Reproduction = high
Dormant = low

2. Environment

Temperature: High = more
Light: High = more
Humidity: High = less
Wind: High = more

3. Soil

Clay = less
Sand = more

4. Plant Characteristics

Succulent = less
Waxy = less
Hairy = less
Fine/thin leaves = more
Deep rooted = less

Go back to the Course Schedule.