Irrigation Application Rate and Production under Centre-pivots Ian McIndoe

1. Irrigation Application Rate and Production under Centre-pivotsIan McIndoe

2. Background • Increasing use of centre-pivot irrigators for irrigating pasture • Increasing length of centre-pivots (200-1400 m radius)

3. Xxx m pivot

4. Xxx m long pivot

5. General Pivot Operation • Waters circular area • Rotation speed typically 1-5 days • Sprinklers 14-18 m apart • Increasing application rate with radius

6. 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

7. 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

8. 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?

9. 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)

10. 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

11. 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

12. 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

13. 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

14. 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

19. Travelling gun, soft hose

20. Hard hose gun

21. Long lateral

22. Solid set

23. K Line

24. Fixed boom, soft hose

25. Rotary boom, soft hose

26. Centre-pivot

27. Spinner

28. Border-dyke