Transcript Slide 1

Irrigation – Does Variability
Matter?
Ian McIndoe
Fraser Scales
Background
• With irrigation, we have to get SMARTer!
– Production
– Drainage (due to irrigation AND rainfall)
– Allocation limits/ water use
– Other factors, e.g. energy
• We need irrigation to be well-designed and
well-managed
• Design sets the platform for high
performance
The challenge
• We live in an imperfect world
• Variability is a fact of life
• Variability has to be accommodated in both
design and management
• Optimum solutions are site specific
What variability?
• Climatic – rainfall, wind, humidity,
temperature
• Agronomic – crop, stage, physical
composition, actual water use
• Soils – PAW, infiltration, depth to pans,
surface storage
• Topographical – shape, slope, infrastructure,
natural features
What variability?
• Water supply – reliability, quantity, quality
• Irrigation system – components, pressure,
flow, uniformity, application intensity
• Management – timing, depth applied
• Given this, how can we deal with variability
to deliver SMART irrigation?
Climate
• Generally, good historical data is available –
useful for determining design specs and
overall need
• For rainfall, need to make full use of local
data
Wind speed
Wind speed
Temperature
Agronomic
• Currently, mostly standard values used to
determine crop water need
• Improved data is being produced – e.g.
grazed pasture crop factors
• Need for irrigation systems to be designed to
better match crop needs
Soils
• Currently, soil maps often used (e.g. S Map)
• Need better information on soil properties
and variability of soils on farm
– PAW and its variability
– Depth to pans/ lower hydraulic conductivity
horizons
• How much does PAW variability matter?
Soil PAW variability
Soil PAW variability
Topography
• Slope matters more than you might think
• Very few paddocks are actually flat
• Surface redistribution is very common
• Need to tailor design and management to
maximise benefits
• Land levelling under spray irrigation?
Application uniformity
• Is about how evenly water is being applied to
the ground surface
• Easily checked using bucket tests
• Low uniformity usually leads to low
efficiency
Spray irrigation bucket test
Application uniformity
Application uniformity
Ponding and surface redistribution
• Probably the biggest contributor to low
irrigation performance
• Can generally be observed
• Driven by application intensity and depth
applied
• Particularly an issue on slopes
• Needs full consideration in irrigation design
and management.
Ponding under pivot
Ponding
Application intensity
Application intensity
Supply reliability
• Impacts on irrigation mind set – just in case
versus just in time
• Impacts on production, water use, drainage
• Need to have high reliability to achieve high
performance
Irrigation system
• Irrigation method
• Pressure variability - tradeoffs
• Flow variability
– issue with VRI, corner arms, multiple pumps
• Voltage variability
• INZ Codes of practice – design, installation
Performance – 60 mm PAW
Performance – 60 mm PAW
Performance – 120 mm PAW
Performance – 120 mm PAW
Irrigation management strategies
• Depth of water applied
• Return interval
• Seasonal limits
• Where and how irrigation is scheduled
• A lot of work has been done and is being
done in this area.
• Weather forecasting will be critical!
Effect of scheduling location
Conclusions
• We need to become SMARTer irrigators
• Variability does matter in some areas
• We need to focus on production, water use
and drainage
• Better engineering will be required
– in the factory: new or improved irrigation methods
– in the design shop
• We need to target application uniformity
• We need to target surface redistribution
Priorities
• What is easy and cost-effective to
implement?
– Some things are well understood
– Some things need to be better communicated to
end users
– Some things require further investigation
• We can achieve our targets, but its not going to
be easy.
Questions
Temperature
Centre-pivot