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Irrigating farmers need to optimise every drop


Media Statement

28 January 2015 – for immediate release

Irrigating farmers need to optimise every drop to stave off drought, says IrrigationNZ

Irrigating farmers need to pull out all the stops to ensure they are optimising every drop of water as the irrigation season may shut down six weeks earlier than usual in some parts of New Zealand threatening the viability of crops and winter feed supply for stock, says IrrigationNZ.

Earlier forecasts that Lake Opuha in South Canterbury may sustain irrigation until the end of February are now being revisited. “The sustained dry conditions have reduced flows across the catchment and increased pressure on our storage prompting us to review the forecast for the lake. Both river flows and irrigation will suffer when we run out of storage,” says Opuha Water Ltd CEO Tony McCormick.

In other parts of Canterbury and Otago, water restrictions are biting home and many farmers say they need to shut down irrigation a month to six weeks earlier than expected given the dry conditions. This will affect their ability to maintain winter feed crops, sow new pastures and ensure stock are in premium condition going into the colder, harsher months.

IrrigationNZ Project Manager Paul Reese says irrigators should ensure their equipment is operating at its optimal level so what-ever water is pumped is applied as effectively as possible. Irrigators also need to be aware of what is happening with their water supply and prepare ahead of further water restrictions to ensure domestic and stock water is still available and that crops can be managed with restricted water supply.

“Scheduling is key, particularly now irrigators are limited in the water they have through seasonal volumes and with water meters in place, so know your soils and how much water your crop uses and apply irrigation accordingly. Groundwater users in particular need to think about their annual volume and where they are at,” he says.

“Ensure your irrigator is working as it should to guarantee you’re getting the best from the water you apply. Checking pressure and sprinklers regularly is essential. If you’re running out of water re-nozzling might help stretch it out for longer or alternatively if you operate a number of irrigation systems think about shutting off the less efficient ones, long laterals in pivot corners for example. That way you can continue to operate more efficient irrigators such as pivots and linear moves for longer,” says Mr Reese.

IrrigationNZ has created a check list of options for irrigators to assist them make the right choices during this dry spell. The options below may not be available to all farmers as they depend on the equipment and set-up of each irrigation system and how farmers react will also depend on their particular water restrictions and land use, says Mr Reese.

“From surface water river takes there may be a rationing regime in place that reduces the water take as certain trigger flows are reached. For example 100 l/s to 75 l/s when the first threshold hits then from 75 l/s to 50 l/s with the next. From an irrigation scheme the roster may change from full flow to reduced flow so your system then has to match it or it could be that the scheme provides full flow but on reduced hours or fewer days. These are all scenarios irrigating farmers now need to prepare for and have contingency plans in place,” says Mr Reese.

Action Pro Con
Deficit irrigate across all of the irrigated area No infrastructure or equipment changes necessary

Scheduling exercise

Keeps the pasture or crop in a green vegetative state

Able to take advantage of small amounts of rainfall across all of the area

Loss of production - pasture approximately 15kg DM/ha per mm of water deficit; feed and arable crops by 0.1-0.2% of potential crop yield per mm of water deficit; vegetable and fruit crop impacts relate to the growth stage.
Take an area out of production No infrastructure or equipment changes necessary

Able to keep the remaining area in full production

Area removed could be prepared for an autumn crop

Loss of production of the area

Depending on irrigation system may be difficult logistically, pivots have varying levels of control for example

Re-nozzle Matches the irrigator demand with restricted supply

If operating with VSD the system can adjust

Cost of changing and restoring to original

Time, cost and lag taken to change and then change back if restrictions are lifted

Results in deficit irrigation

Mismatch of fixed duty pumps to reduced flow

Reduced energy efficiency

Prioritise crops or areas Can concentrate available water onto highest paying crops or best pastures Reduced production of remaining crops or areas


IrrigationNZ is the national body representing irrigators and the irrigation industry. Its mission is to promote excellence in irrigation throughout New Zealand.

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