Irrigation – Does Variability Matter?

Ian McIndoeFraser 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