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 1 ¼ 1 ½ 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