1. Importance of water Turfgrasses composed of 75-85% water by weight
Turfgrasses begin to die if the water content drops below60 to 65% by weight for a short period.

2. Soil Water Storage
Soil as a reservoir from which turfgrasses draw water
Water is held by two forces: a. adhesive forces; the
adhesion of water to soil particles; b. cohesive forces; the
Attraction of water molecules for each other.
The soil may be compared to a sponge, made up of solid
particles and the spaces between them. Water is held in films
Surrounding the particles and in the spaces between the
particles.

3. Soil Water Storage Soil water retention forces
The forces holding water in soils are generally expressed
in bars.
Classic water potentials are; 0 bars when the soil is fully
Saturated, -0.3 bars at “Field Capacity”, and -15 bars
At the point when plants become permanently wilted.

4. Water infiltration rate of soils
Water infiltration rate = rate at which water enters the soil.
Water percolation rate = rate at which water passes through
the soil..

5. Soil Texture Soil Texture: The size of the individual soil particles.
Soil textural classes: (particle diameter in millimeters)
Sand:
Very Coarse Sand mm
Coarse Sand mm
Medium Sand mm
Fine Sand mm
Very Fine Sand mm
Silt mm
Clay - less than mm

6. Soil Structure Soil structure is the arrangement of individual particles into aggregates. Factors in formation of soil structure; a. electrostatic bonds (Ca++, Mg++, Al+++). b. cementing agents formed in decomposition of organic matter.

7. Effects of soil texture
Soil texture Available water water infiltration
(in./ft.) rate (in./hr.)
Sands to to 0.5
Sandy loam to to 0.35
Silt loam to to 0.25
Clay loam to to 0.2
Clay to to 0.05

8. Effects of soil texture and slope on water application rate
Water application rate (in./hr)
Amount of slope
Soil texture 0-5% 5-10% >10%
Sands
Sandy loam
Silt loam
Clay loam
Clay

9. Approx. amt. of H2O to remove from different soils
Appearance desired
Soil text. Vigorous Strong Mod. Low Min.
Sand
Loamy sand
Sandy loam
Loam
Clay (poor
Structure)
Clay (good
structure)

10. Water additions to soil
Precipitation
Rain, snow, etc.
Irrigation

11. Water removal from soil
Run off
Drainage through the soil to lower depths
Evaporation from the soil surface
Transpiration by plants
Evaporation minimal after turf covers soil
Evapotranspiration =Evaporation +
Transpiration

12. Factors influencing ETrateee
Temperature
Light intensity and duration
Humidity
Wind velocity
Species of grass being used
Water content of the soil
Soil texture and structure
Extent of the root system
Cultural practices

13. Irrigation amount and frequency
Over watering may be as detrimental as under application
Shallow-frequent watering effects
Short root systems
Increased susceptibility to soil compaction
Increased disease susceptibility
Preferred method of irrigation is to the depth of the root
System as frequently as needed to prevent severe water stress

14. When to irrigate By calendar (set automatic timers)
Visual observation of turf
Evaporation pans
Tensiometers
Electrical resistance
Predictive models based on weather station data

15. Visual observation Visual observation of turf conditions
Moisture stressed plants have different color
Moisture stressed plants recovers slowly when
walked on (foot printing)
This method requires experience and constant
monitoring
May result in severe stress in critical areas

16. Evaporation pan ET is correlated to the rate at which water evaporates
from pan
ET of warm season grasses less than that of cool
season grasses
Environmental conditions in specific areas may be
different from that where pan is located

17. Factors used to obtain ET of grasses from pan evaporation
Type of growth desired C3 grasses C4 grasses
Vigorous, lush
Strong growth,
acceptable appearance
Moderate growth,
marginally acceptable
from Handreck, H.K. and Black Growing media for ornamental plants and turf. NSW Press.

18. Tensiometer
Hollow, water filled tubes with porous ceramic cup in soil. Vacuum meter at top measures water tension.
Measure soil moisture tension at specific areas
Require frequent servicing
May interfere with use of turf area

19. Water use by bermudagrass turf
Irrigation Annual water use
schedule (mm) % of “normal” Turf Quality*
Tens. at 15 kPa
Tens. at 40 kPa
Tens. at 65 kPa
76 % of pan evap
“Normal practice
_______________________________________________
Rated on a scale of 10= best, 1- poorest. No significant
differences except the”normal practice contained more
Annual bluegrass.

20. Electrical resistance or conductance
Porous blocks which absorb moisture
Soil moisture probes
Both attempt to measure electrical resistance or
Conductance
Conductance greatly influenced by salts in soil moisture
(Soil moisture meter will read very dry in distilled water)

21. Predictive models Modified Penman equation
requires much environmental data
Hargraves equation
much less environmental data required
worked as well or better than Modified
Penman in Hawaii

22. Water quality Primary concerns Total salt concentration (salinity)
Concentration of Sodium and other cations

23. Salinity hazard Salinity measured as electrical conductivity(dS/m,
Mmhos/cm), ppm solubles salts etc.) dS/m=mmhos/cm
ppm soluble salts/640 =dS/m
<0.25 dS/m = suitable for all turfgrass irrigation
0.25 to 0.75ds/m =generally no problem
0.75 to 2.25 ds/m =Salt tolerant species and good drainage
>2.25=good drainage, use of very salt tolerant plants,
leaching of soil, and use of gypsum

24. Sodium Hazard Sodium adsorption ratio (SAR)
SAR= Na/ [(Ca+++Mg++)/2]1/2
SAR 0 to 10.0 = low sodium hazard
SAR 6.5 to 18.0 =appreciable sodium hazard. Cam be used on sandy soils with low CEC
SAR 12.0 to 26.0= appreciable sodium hazard. Use only on sandy soils with low CEC and likely will require special soil mgt. practices.
SAR>12.0 to 26.0= unsuitable for irrigation purposes.

25. Irrigation Water Composition
Parameter Desired range Average reclaimed pH
EC (ds/m) <
HCO3- (ppm) <
Na+ (ppm) <
Cl- (ppm) <
SO4-- <
Average reclaimed=average values for reclaimed water in U.S. (secondary treated sewage effluent)

26. Soil solution salinity tolerance of turfgrasses (dS/m2)
Salt tolerance of turfgrasses grown in solution culture.
Species EC(dS/m) at 50% yield reduction
Zoysiagrass 37
Bermudagrass 28
Seashore paspalum 26
St. Augustinegrass 24
Tall fescue 13
Perennial Ryegrass 12
Creeping bentgrass 10
Centipedegrass 9

27. Managing Saline irrigation water
Must leach salts from soil
Leaching fraction (LF)
LF=Eci/Ecd
where: Eci= electrical conductivity of irrigaton
water
Ecd= desired electrical conductivity of
soil solution