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 mm Coarse Sand mm Medium Sand mm Fine Sand mm Very Fine Sand mm Silt mm Clay -less than mm

CLM Soil Structure Factors in formation of soil structure; a. electrostatic bonds (Ca++, Mg++, Al+++). b. cementing agents formed in decomposition of organic matter. 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 textureAvailable waterwater infiltration (in./ft.) rate (in./hr.) Sands 0.5 to to 0.5 Sandy loam 1.0 to to 0.35 Silt loam 1.5 to to 0.25 Clay loam 1.5 to to 0.2 Clay 1.5 to to 0.05

CLM Effects of soil texture and slope on water application rate Water application rate (in./hr) Amount of slope Soil texture0-5%5-10%>10% Sands Sandy loam Silt loam Clay loam Clay

CLM Approx. amt. of H 2 O to remove from different soils Appearance desired Soil text.VigorousStrong Mod. Low Min. Sand Loamy sand Sandy loam Loam Clay (poor Structure) Clay (good structure)

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 C 3 grasses C 4 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.

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 Annual water use schedule(mm) % of “normal” Turf Quality* Tens. at 15 kPa Tens. at 40 kPa Tens. at 65 kPa % 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.

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 Irrigation Water Composition ParameterDesired range Average reclaimed pH EC (ds/m)< HCO3- (ppm)<90200 Na+ (ppm)< Cl- (ppm)< SO4--<200197

CLM Soil solution salinity tolerance of turfgrasses (dS/m 2 ) Salt tolerance of turfgrasses grown in solution culture. SpeciesEC(dS/m) at 50% yield reduction Zoysiagrass37 Bermudagrass28 Seashore paspalum26 St. Augustinegrass24 Tall fescue13 Perennial Ryegrass12 Creeping bentgrass10 Centipedegrass 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