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Irrigation Scheduling
Using ET and Soil
Based Methods
Loren Oki UC Davis Department of Plant Sciences and
Landscape Architecture Program – Dept. Env. Design
River-Friendly Landscaping Strategies for Parks
Sacramento, CA January 25, 2012
Topics
• Why do we need to conserve?
• Different control methods
• Other things to consider
•Irrigation Management
•Photos: D. Haver
“Urban Drool”
•Photos: D. Haver
Irrigation Systems
• Control – “Hand”
When and how much
to apply irrigation is
determined by
direct observation of
the grower/irrigator
Photo: L. Oki Photo:UC IPM
Irrigation Systems
• Control – Timers
Irrigation is applied
based on a fixed,
predetermined
schedule
Photo: L. Oki
• Control
– Sensors
Irrigation Systems
Moisture sensing devices
e.g., Tensiometers
Tube
Ceramic cup
Gauge
Water loss
Graphic: L. Oki
Irrigation Systems
• Control
– Sensors
Moisture sensing devices
e.g., Tensiometers
Photo: L. Oki
Soil Moisture-Based Irrigation
Valve
Emitter
Water in
Tensiometer
Transducer
Graphic: L. Oki
Interface
Input
channels
Output
channels/
relays
Controller
Irrigation Systems
• Control
– Sensors Granular matrix (gypsum blocks)
Photo: L. Oki
Irrigation Systems
• Control
– Sensors Time domain reflectometry (TDR)
Photo: L. Oki
Irrigation Systems
• Control
– Sensors Dielectric permittivity
Photo: L. Oki
Irrigation Systems
• Control
– Sensors Tensiometers
Granular matrix (gypsum blocks)
Time domain reflectometry (TDR)
Dielectric permittivity
Irrigation Systems
• Control
Conductance-based
sensors are NOT
appropriate
Irrigation Systems
• Control
– Water use
models • Based on weather data
• Requires previous research
• Crop specific
• Easy to use
Irrigation Systems
• Control
– Water use
models • Light accumulation
• Evapotranspiration (ET)
“weather-based”
Irrigation Systems
• Control
– Water use
models
CIMIS
C alifornia
I rrigation
M anagement
I nformation
S ystem
Water use reports are used with
a crop or landscape coefficient
to estimate site water use
wwwcimis.water.ca.gov
Irrigation Systems
• Control
– Water use
models
CIMIS
Reference ET (ET0) is reported
Crop coefficient (Kc) is necessary
Determine ETcrop (ETc) to estimate
crop water use
so, ETc=ET0 x Kc
Example: citrus orchard
Kc = 0.65
If ET0 = 0.5”, then
crop water use is 0.325”
(0.325=0.5 x 0.65)
Irrigation Systems
• Control
– Water use
models
CIMIS
Reference ET (ET0) is reported
Crop coefficient (Kc) is necessary
Determine ETcrop (ETc) to estimate
crop water use
so, ETc=ET0 x Kc
• Can this system be utilized in an
urban landscape?
• Water budgets are now required
by law in new and renovated
landscapes.
Irrigation Systems
• Control
– Water use
models
Weather-based controllers
Issues • Set up
WUCOLS Water
Use
Classification
Of
Landscape
Species
Irrigation Systems
• Control
– Water use
models
Weather-based controllers
Issues • Set up
SLIDE Simplified
Landscape
Irrigation
Demand
Estimation
Irrigation Systems
• Control
– Water use
models
Weather-based controllers
Issues • Set up
• Complexity
• Maintenance
Irrigation Systems
ETo Zones Map
Irrigation Systems
• Control
– Sensors
– Water use
models
• Based on soil moisture
• Based on weather data
• ETo
Irrigation Systems
• Control
– EPA Water Sense
– Irrigation Association SWAT tested
Irrigation Management Other Things to Consider
For Weather-Based irrigation
Program modification method
Fixed schedule, Modify on-time
Modify schedule, Fixed on-time
Irrigation Management Other Things to Consider
For Weather-Based irrigation
Program modification method
Irrigation Management Other Things to Consider
For Weather-Based irrigation
Program modification method
0
1
2
3
4
5
6
7
8
9
10
Jan Feb Mar apr May Jun Jul Aug Sep Oct Nov Dec
inches
Irrigation Management Other Things to Consider
For Weather-Based irrigation
Program modification method
0
1
2
3
4
5
6
7
8
9
10
Jan Feb Mar apr May Jun Jul Aug Sep Oct Nov Dec
inches
100%
90% 90% 80%
60%
40%
25% 20% 20%
25%
50%
65%
3 days
6 days
12 days
Irrigation Management Other Things to Consider
Application and infiltration
Be sure that the
application rate of the
irrigation system is less
than the infiltration
rate of the soil.
Irrigation Management Other Things to Consider
Be sure that the
application rate of the
irrigation system is less
than the infiltration
rate of the soil.
Irrigation Management Other Things to Consider
Hydrozoning
Group plants with similar water use
rates together within an irrigation
zone
Sun vs. Shade
Irrigation Management Other Things to Consider
Water Quality
Irrigation using lower quality water,
such as reclaimed water, needs to
be properly managed.
Irrigation Management Other Things to Consider
Training and Certification
California Landscape Contractors Association (CLCA)
Water Management Certification Program
http://www.clca.us/water/index.html
