WATER

“…the rain and the snow come down from heaven, and do not return there without watering the earth and making it bear and sprout, and furnishing seed to the sower and bread to the eater…”     —Isaiah 55: 10

Nutrients are dissolved in water H₂O

Properties of Water

1. Hydraulic (does not compress so pressure is possible, turgor support)
2. Wonderful Solvent (widest range of possible solutes, transpiration, translocation)
3. Reactant or Product of Reactions (photosynthesis & respiration)
4. High Specific Heat (much heat gives little change in temperature, heat buffer)
5. High Heat of Fusion (evaporating liquid water takes energy away, 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 = most important on this list from a plant point of view!
5. Aquifers and springs

Horizon A = leached topsoil
Horizon B = accumulated subsoil

Erosion fits in here somewhere!

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-as in our greenhouse

-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

This page © Ross E. Koning 1994.

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Send comments and bug reports to Ross Koning at rkoning@snet.net.