Using Flux Measurements to Determine Sprinkler Irrigation Efficiency at Biosphere 2

H.D. Adams1,2, L.M. Benton2, M.L. Cavanaugh2, J.R. Martin2, A.L. Neal3, S. Rajagopal3, R. Rosolem3, A.P. Tyler1, J.C. Villegas2

1Dept. of Ecology and Evolutionary Biology, 2School of Natural Resources, 3Dept. of Hydrology and Water Resources

The University of Arizona, Tucson, AZ

IntroductionLawns, golf courses, sport fields and other

areas planted in turfgrass are common, important components of urban systems

Effective and efficient irrigation management is:important economically and ecologicallyrequired for turfgrass function, particularly in

water-limited areas

IntroductionArizona: ~18,200 hectares of

golf courses (Schmidt 2006)

Many, many more hectares of turfgrass in urban areas being irrigated

Are these facilities and residences making an effort to maximize water use efficiency of their lawns?

turfgrass.unl.edu

IntroductionWhy Bermudagrass?

Grass of choice in southern USTolerates high sunlight and

high air temperaturesAble to grow in shallow soil

conditions and withstand trampling

Can tolerate salty water, salty soil conditions

Needs little water once established

www.answers.com

IntroductionBermudagrass requires:

508 mm of precipitation inputs needed for survival762 mm for acceptable color 1016 mm for adequate color and growth

Oracle, AZ received less than

500 mm, so irrigation

is necessary

www.lawnsprinklers.us

ObjectivesTo establish the pre-response conditions of turfgrass

under early-season, pre-watering conditionsTo measure and consider influence of environmental

variables on turfgrass phenology, including measurements of:carbon, water and energy flux via eddy covariancedistributed soil moisture and soil salinitythe distribution of applied water from the sprinkler irrigation

system on-siteProvide suggestions for efficient irrigation

management at Biosphere 2

Why Care?Better irrigation efficiency at Biosphere 2

lawn makes sense economically and environmentally

Reduces chance of high soil salinity from over-watering

Potential to guide irrigation regimes in other turfgrass areas of similar climate

Brides like nice grass (Biosphere weddings!)

www.redflagdeals.com

Jeffrey, isn’t it lovely to have efficiently irrigated grass at

our Biosphere wedding?

Doesn’t she mean Biodome?

Field SiteBiosphere 2, Oracle, AZ

~56.3 km North of TucsonElevation: 1378 m

Average Annual TemperatureMaximum: 23.55oCMinimum: 9.94oCFebruary to April - Max: 18.83oC, Min: 4.94oC

Average Annual Precipitation: 492.8mmFebruary to April: 109.2mm

Soil: loam and fill

Be sure to visit the Chalet Village

www.pbase.com

Field SiteLocated on north side of

Biosphere 2Lawn area ~1.24 acresSurrounded:

South and East sides by buildings

North and west sides by large berm

Field SiteSouth Tower

Daytime predominant

wind direction

Field Site

South Tower

North Tower

Sprinklers

Methods Tower Instrumentation and Variables Measured

3-D sonic anemometer (wind direction and speed)

Infrared gas analyzer (fCO2, fH2O)

Net radiometer (Rnet)

CR5000 Datalogger collected data

MethodsOther Site Instrumentation – Automated

Ground heat flux plates (G)TDR soil water content probes (automated θ)Tipping bucket (P)

Point MeasurementsRain gauges placed at equal intervals across field

Spatial irrigation inputs measured every 2 weeks

EM38 (relative soil salinity) Measured at each grid point every 2 weeks

Hydrosense (manual θ) Measured at each grid point every 2 weeks

Methods – Tower Comparison

Latent Heat

SensibleHeat

Carbon Flux

Methods – Energy Balance Closure

Half Hourly Daily

Methods – 2D Schmid Footprint

P=0.5 source area for westerly winds (+/- 30°)

Rule of thumb (1:100) would need 175 m in direction of mean wind (total source area). Gash (1986) model says 240 m in direction of mean wind. We have 80-100m of lawn, large berm, desert flora.

Full source area 4/17/08

Results – Soil Moisture

Initial Dry Down – Irrigation Period – Intense (2 hours / station) Irrigation Period

Results – Diurnal Energy

Pre-Irrigation Data looks reasonable, Wide range of “morning” LE

Sensible Heat

Latent Heat

Ground Heat Flux Net Radiation

Irrigation results in higher LE – driven by water or available energy?

Results – Diurnal Energy

Sensible Heat

Latent Heat

Ground Heat Flux

Net Radiation

Results – Diurnal CO2

CO2 flux doesn’t change much – perhaps increase in LE is just E at this point.

mg/

m2 s

Results - Grid Soil Moisture

Soil moisture for day 1, before irrigation

Eddy Tower

Results – ET time series

ET near ETcrop during initial watering, above ETcrop (near ETo) during intensive watering

Results - Salinity

No real salty spots!Found out where the Tubing is!

Results - Sprinkler Irrigation

Irrigation as measured by precipitation gage grid

Units Check!

Results - Grid Soil Moisture

Soil moisture for day 3, after irrigation

Results - Grid Soil Moisture

Irregularity in soil moisture due to irregular sprinkler irrigation

Discussion Point – Irrigation Efficiency IndexTwo Indices were developed

IUE 0 IUE > 0, overwatering

IUErel1

IUErel >1, overwatering

I

ETIIUE crop

tower

croprel ETI

ETIIUE

Show plot here

Discussion Point – Irrigation Efficiency Index

Wet spots based on grid data are at “30, 25”, are we catching this at the south tower?? Maybe if we just used north tower…

Discussion Point – Positioning is important.

Wet spot Wet spot

ConclusionsTowers can be used on lawn at Biosphere 2Salinity effect many not be evident due to use of well

waterIrrigation efficiency can be improved

Early irrigation schedule is near idealLate schedule (double-watering) is overwatering

Spatial coverage of sprinklers is poorHighly variable soil moisture across lawnPoor drainage in some locations near edge of lawnSprinkler operation may be defective!

Proposed Future of TowersLook for green-up in CO2 signal

Plants may not be fully active during irrigation studySoil respiration may offset signal in early spring

Comparison of records between towersError analysis using co-located measurementsDistribution of soil moisture, footprints

Irrigation during summer monthsWill the towers be there?

RecommendationsIrrigate during nighttime

Reduce ET lossesPromote increase in soil moisture

Irrigate with less waterConsider timing of operation of each sprinkler headSpatial distribution of water and resultant soil moisture

Improve drainage Prevent water-logging

Consider use of reclaimed waterWhat about salinity associated with this?

AcknowledgmentsWe would like to thank:

• Shirley Kurc, Jim Shuttleworth, and Travis Huxman for their guidance on this project

• John Adams, and the many Biosphere 2 staff members who assisted us throughout the semester

• Greg Barron-Gafford at the University of Arizona for his help in providing instruments

• James B. Callegary at the USGS for use of his EM38

• Dave Breshears at the University of Arizona for use of his soil moisture and eddy covariance equipment

Henry

Juan