Irrigation Application Rate and Production under Centre-

pivots

Ian McIndoe

Background

• Increasing use of centre-pivot irrigators for irrigating pasture

• Increasing length of centre-pivots (200-1400 m radius)

Xxx m pivot

Xxx m long pivot

General Pivot Operation

• Waters circular area

• Rotation speed typically 1-5 days

• Sprinklers 14-18 m apart

• Increasing application rate with radius

The Problem

Reduced application efficiency because of:

• Application rate often exceeding infiltration rate of soil

• Surface ponding

• Surface redistribution leading to drainage through soil profile

• Potential runoff

• Significant variability in soil and irrigation parameters

Why is it a Problem?

• Cost of applying extra water to compensate for dry areas

• Seasonal allocation limits constrain total seasonal use

• Leaching of nutrients (water quality implications)

• Wheel ruts and downtime due to pivots getting stuck

• Loss of production

Dilemma

• Short pivots cost significantly more per hectare irrigated than long pivots

• Long pivots can result in loss of production and lower application efficiency due to high application rates.

Where is the tradeoff?

Previous work • NZAEI research on irrigator application rate

and uniformity

–Focussed on what happens between the irrigator nozzles and ground level

–Did not investigate what could happen in the soil

–Did not include centre-pivots• Bloomer research on quantifying surface

redistribution (MAF SFF)

Alternative Approach

• Marshall English (Oregon State University):

–Used an approach that combined climate, soil and irrigation parameters statistically to determine crop yield and irrigation efficiency

• Aqualinc adapted the English approach to:

–Use historical daily climate data–Model typical NZ irrigation strategies–Expand the analysis to consider water use and

production under centre-pivots

Irrigation and Soil Parameters

• Marshall English (Oregon State University):

–Used an approach that combined climate, soil and irrigation parameters statistically to determine crop yield and irrigation efficiency

• Aqualinc adapted the English approach to:

–Use historical daily climate data–Model typical NZ irrigation strategies–Expand the analysis to consider water use and

production under centre-pivots

What Constrains Efficient Irrigation

• Unreliable water supplies• Lack of supply or operational flexibility• Unwanted stoppages• Limited user training• Poor design• Limited or no system auditing• Limited or no soil moisture measurement• Limited or no use of irrigation performance

measures

Factors Contributing to Improved Irrigation Efficiency

• Attitude – normal farm input, not just drought insurance

• Planned inputs delivering planned outputs

• Design of farm around irrigation system - layout

• Optimal use of labour, capital and energy

• Systems matched to range of soil and plant requirements – good design, on-demand supply

• Piped water schemes, use gravity as much as possible

• Measurements and monitoring for good operation

• Good maintenance

• Use of performance measures

Some things to look for

• General impression

• Operator experience and know how

• System flexibility – matched to crop/soil requirements

• Application uniformity and intensity

• Good maintenance

• Water and soil moisture measurement and use of information

• How rainfall is used – risk management

• Record keeping

Travelling gun, soft hose

Hard hose gun

Long lateral

Solid set

K Line

Fixed boom, soft hose

Rotary boom, soft hose

Centre-pivot

Spinner

Border-dyke