Importance of water

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 -- 2.0 - 1.0 mm Coarse Sand - 1.0 - 0.5
mm Medium Sand - 0.5 - 0.25 mm Fine Sand
- 0.25 - 0.1 mm Very Fine Sand - 0.1 - 0.05
mm Silt - 0.05 - 0.002 mm Clay - less
than 0.002 mm
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Soil StructureSoil 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 0.5 to 1.0 1.0 to
0.5 Sandy loam 1.0 to 1.5 0.75 to 0.35 Silt
loam 1.5 to 2.0 0.4 to 0.25 Clay loam 1.5
to 2.0 0.3 to 0.2 Clay 1.5 to 2.0 0.15 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 gt10 Sands 0.8
-0.4 0.6-0.3 0.4-0.2 Sandy loam 0.6-0.3 0.45-0.22
0.3-0.15 Silt loam 0.35-0.2 0.3-0.15 0.2-0.1 Cla
y loam 0.25-0.2 0.2-0.15 0.15-0.1 Clay 0.1-0.05
0.1-0.05 0.05-0.00
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Approx. amt. of H2O to remove from different
soils
Appearance desired Soil
text. Vigorous Strong Mod. Low
Min. Sand 0.36 0.48 0.56 0.72
0.72 Loamy sand 0.48 0.72 0.84
0.96 1.08 Sandy loam 0.72 1.20
1.32 1.44 1.56 Loam 1.08 1.80
2.04 2.16 2.24 Clay (poor Structure)
0.60 0.96 1.20 1.32 1.56 Clay
(good structure) 0.84 1.32 1.56
1.92 2.28
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Water additions to soil
Precipitation Rain, snow, etc. Irrigation
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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

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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
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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 Environment
al 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 0.8 - 0.85 0.55- 0.70
• Strong growth,
• acceptable appearance 0.70- 0.75 0.45-
  0.55
• Moderate growth,
• marginally acceptable 0.65- 0.70 0.25-
  0.40
• from Handreck, H.K. and Black. 1984. Growing
  media for ornamental plants and turf. NSW Press.

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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 850 62 8.8 Tens. at 40
kPa 670 50 8.2 Tens. at 65 kPa 590 44 7.8 76
of pan evap 1010 76 8.5 Normal
practice 1330 100 7.5 __________________________
_____________________ Rated on a scale of 10
best, 1- poorest. No significant differences
except thenormal 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/mmmhos/cm ppm soluble salts/640
dS/m lt0.25 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 gt2.25good drainage, use of
very salt tolerant plants, leaching of soil, and
use of gypsum
24
Sodium Hazard
Sodium adsorption ratio (SAR) SAR Na/
(CaMg)/21/2 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. SARgt12.0 to 26.0 unsuitable for
irrigation purposes.
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Irrigation Water Composition

• Parameter Desired range Average reclaimed
• pH 6.5-7.0 7.2
• EC (ds/m) lt1.2 1.1
• HCO3- (ppm) lt90 200
• Na (ppm) lt160 147
• Cl- (ppm) lt100 197
• SO4-- lt200 197

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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 2
8 Seashore paspalum 26 St. Augustinegrass 24 T
all fescue 13 Perennial Ryegrass 12 Creeping
bentgrass 10 Centipedegrass 9
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Managing Saline irrigation water
Must leach salts from soil Leaching fraction
(LF) LFEci/Ecd where Eci electrical
conductivity of irrigaton water Ecd
desired electrical conductivity of soil
solution