Louisiana Yards and
Neighborhoods
Water
Efficiently!
www.lsuagcenter.com/lyn
Water efficiently!
• Plants
• Soils
• Systems
• Mechanics
Plants
• Plant water needs
• Water movement
• Evaporation and transpiration
• Evapotranspiration
• ET-LAIS (EvapoTransporation values from
Louisiana Agriclimatic Information System)
• Temperature vs. relative humidity
Plant Water Needs
• Germination
• Vegetative phase
• Reproductive phase
• Transpiration cools plant, provides suction
to pull water and nutrients from the soil
into roots
• Plants have differing water needs
Water Movement
Evaporation and Transpiration
• Evaporation dominates vegetative phase of
growth and increases with increased
frequency of irrigation.
• Transpiration dominates reproductive phase
of growth and is affected by plant density,
mono-culture/mixed bed, exposure to sun,
wind and built environment.
Evapotranspiration
ET-LAIS
• To find ET values at LAIS weather
stations:
http://www.lsuagcenter.com/weather/Etotabledata.asp
• A description of ET use:
http://www.lsuagcenter.com/weather/potentialUseOfETOData.asp
Temperature vs. Relative Humidity
Soil (or Media)
• Porosity
• Permeability
• Field capacity
• Wilting point
• Available water holding capacity
• Soil texture
• Water intake rate and depth
• Compaction
Soil – Porosity
• Volume of pore space within a given
volume of soil (%).
• Pore spaces are available for air and/or
water and/or roots.
• When soil is saturated with water, there
is no room for air.
• Roots (of most plants) will not grow
into water.
Soil – Permeability
• How fast can water move into/through
soil (inches/hour)?
• Higher in dry soil, lower in wet soil
• Higher in soils with larger pore spaces
(sands, loams)
• Lower in soils with smaller pore spaces
(silts, clays)
Soil – Field Capacity
• Moisture content of soil 24-48 hours after
saturation.
• Gravity causes “free” water to drain down
below root zone.
• Air moves into pore spaces as water drains.
• Water is readily available to plant.
• Moisture content at field capacity may be:
sand – 10%, silt loam – 20%, clay – 50%.
Soil - Wilting Point
• Moisture content of soil after plant has
removed all the water it can.
• Moisture content at wilting point may be:
– Sand 1%
– Silt loam 5%
– Clay 25%
Soil – Available Water-holding
Capacity
• Available water holding capacity (AWHC) =
field capacity minus wilting point.
• AWHC for sand may be 10%-1% = 9%, or .09 x
12 inches/foot = 1.08 inches/foot.
• AWHC for silt loam may be 20%-5% = 15%, or
.15 x 12 inches/foot = 1.8 inches/foot.
• AWHC for clay may be 50%- 35% = 15%, or .15
x 12 inches/foot = 1.8 inches/foot
Soil – Compaction
• Compaction reduces both porosity and
permeability.
• Compaction can be increased by traffic,
tillage and chemical changes such as
adding sodium or calcium.
• Soil compacts easily when wet.
Systems
• Garden furrow irrigation
• Lawn sprinkler irrigation
• Drip or micro irrigation
Systems – Garden Furrow Irrigation
• High losses of water to evaporation and
percolation below root zone
• Low distribution uniformity as water travels
down the row
• Short-term saturation of soil pore spaces
• Wet furrows after irrigation
Systems – Lawn Sprinkler Irrigation
• If properly designed, installed,
maintained and operated, sprinklers
provide most efficient means for
uniform irrigation of lawns.
• Higher pressure requirements: 30-60
pounds per square inch (psi) than
furrow or drip irrigation.
• Easily automated.
Systems – Drip/Micro Irrigation
• Facilitates daily or more frequent irrigation
to reduce plant moisture stress
• Low pressure requirements: 10-15 pounds
per square inch (psi)
• Low flow rates: gallons per hour (gph)
instead of gallons per minute (gpm)
• Easily modified as needed
Mechanics
• Basics
• Flow restrictions
• Schedule 40 PVC pipe flow rates
• Drainage
Mechanics – Basics
• Flow rate: gallons/minute (gpm) or
inches/day.
• Pressure: pounds/square inch (psi).
• Pressure is lost from pipe friction and other
restrictions to flow.
• Freeze protection: exposed PVC is at risk
below 20 degrees.
• Backflow protection is essential.
Mechanics – Basics
(continued)
• Electronic controllers available to
automate system.
• Filtration is essential for drip or micro
systems.
• Water quality: check pH, salts, sodium,
iron, manganese, calcium.
• Chemigation is possible.
• Maintenance is essential.
Mechanics – Flow Restrictions
• Water flowing through a pipe creates friction,
which reduces pressure.
• Changing water flow direction reduces
pressure.
• The labor to install a 1-inch pipe is the same
as for a ¾-inch pipe, but friction losses are
greatly reduced.
Mechanics – Schedule 40 PVC Pipe
Flow Rates
Diameter (in)
½
¾
1
1¼ 1½ 2
Flow (gpm)
4
8
12
22
30
50
Velocity (ft/sec)
4.2
4.8
4.4 4.7
4.7
4.8
Loss (psi/100’)
5.6
5.1
3.4 2.7
2.3
1.7
Mechanics – Drainage
• Design landscape to drain.
• Surface drainage is the only practical
solution.
• Subsurface drainage is absolutely the last
resort.
• Divert drainage coming onto landscape from
your roof, driveway or your neighbor’s yard.
Louisiana Yards and
Neighborhoods
Water
Efficiently!
www.lsuagcenter.com/lyn