CLM

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 .

CLM

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.

CLM

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.

CLM

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..

CLM

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

Silt Clay

Very Fine Sand 0.1 - 0.05 mm 0.05 - 0.002 mm less than 0.002 mm

CLM •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.

CLM

Effects of soil texture

Soil texture Sands Sandy loam Silt loam Clay loam Clay Available water (in./ft.) 0.5 to 1.0

1.0 to 1.5

1.5 to 2.0

1.5 to 2.0

1.5 to 2.0

water infiltration rate (in./hr.) 1.0 to 0.5

0.75 to 0.35

0.4 to 0.25

0.3 to 0.2

0.15 to 0.05

CLM

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 0.8-0.4

0.6-0.3

0.35-0.2

0.25-0.2

0.1-0.05

0.6-0.3

0.45-0.22

0.3-0.15

0.2-0.15

0.1-0.05

0.4-0.2

0.3-0.15

0.2-0.1

0.15-0.1

0.05-0.00

CLM

Approx. amt. of H

2

O to remove from different soils

Soil text.

Sand Loamy sand Sandy loam Loam Vigorous 0.36

0.48

0.72

1.08

Clay (poor Structure) Clay (good structure) 0.60

0.84

Appearance desired Strong Mod. Low 0.48

0.56

Min.

0.72 0.72

0.72

0.84 0.96 1.08

1.20 1.32 1.44 1.56

1.80

2.04

2.16

2.24

0.96

1.32

1.20 1.32 1.56

1.56 1.92 2.28

CLM

Water additions to soil

Precipitation Rain, snow, etc.

Irrigation

CLM

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

CLM

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

CLM

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

CLM

When to irrigate

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

CLM

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

CLM

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

CLM

Factors used to obtain ET of grasses from pan evaporation

Type of growth desired Vigorous, lush Strong growth, C 3 grasses 0.8 - 0.85

acceptable appearance 0.70- 0.75

Moderate growth, marginally acceptable 0.65- 0.70

C 4 grasses 0.55- 0.70

0.45- 0.55

0.25- 0.40

from Handreck, H.K. and Black. 1984. Growing media for ornamental plants and turf. NSW Press .

CLM

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

CLM

Water use by bermudagrass turf

Irrigation schedule Tens. at 15 kPa Tens. at 40 kPa Tens. at 65 kPa Annual water use (mm) 850 670 590 % of “normal” Turf Quality* 62 50 44 8.8

8.2

7.8

76 % of pan evap 1010 “Normal practice 1330 76 100 8.5

7.5

_______________________________________________ Rated on a scale of 10= best, 1- poorest. No significant differences except the”normal practice contained more Annual bluegrass.

CLM

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)

CLM

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

CLM

Water quality

Primary concerns Total salt concentration (salinity) Concentration of Sodium and other cations

CLM

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

CLM

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 .

CLM

Irrigation Water Composition

Parameter pH EC (ds/m) Desired range 6.5-7.0

<1.2

HCO3- (ppm) Na+ (ppm) Cl- (ppm) SO4- <90 <160 <100 <200 Average reclaimed 7.2

1.1

200 147 197 197

CLM

Soil solution salinity tolerance of turfgrasses (dS/m

2

)

Salt tolerance of turfgrasses grown in solution culture.

Species Zoysiagrass Bermudagrass Seashore paspalum St. Augustinegrass Tall fescue Perennial Ryegrass Creeping bentgrass Centipedegrass EC(dS/m) at 50% yield reduction 37 28 26 24 13 12 10 9

CLM

Managing Saline irrigation water

Must leach salts from soil Leaching fraction (LF) LF=Ec i /Ec d where: Ec i = electrical conductivity of irrigaton water Ec d = desired electrical conductivity of soil solution