Water scheme flows into Canterbury Plains
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More than half of Central Plains Water's (CPW) 60,000 hectare coverage area was already under irrigation even before water started flowing in the scheme in September.
About 33,000ha was under existing irrigation, CPW environmental general manager Susan Goodfellow said.
"This irrigation water was mainly underground extraction and over-allocated. For these farmers the goal is to stop extracting from groundwater and switch to surface water supplied by the scheme."
The remaining 27,000ha was dryland farming that would convert to surface water irrigation.
Of the 23,000ha at Te Pirita and Hororata which started receiving water in September as part of stage one, 60 per cent was already irrigated and only 30 per cent dryland.
In comparison, the ratio in stage two, covering 33,500ha around Darfield and 3500ha at Sheffield, was an even split of irrigated and dryland.
"Being dryland, it is a much harder investment decision for these farmers in terms of the money required. It is equivalent to buying their farm again.
However, many are taking a long-term view. Whereas, for many stage one farmers it was just a matter of switching from one water source to another," Goodfellow told a forum on sustainable farming systems at Lincoln University, hosted by the New Zealand Institute of Agricultural and Horticultural Science Inc.
CPW has just kicked off its stage two farmer engagement, seeking funding for the balance of the scheme which had concept plans underway.
A total of 380 farmers own shares in the scheme. An open headrace canal will eventually stretch 56km between the Rakaia and Waimakariri rivers, with other parts of the irrigation scheme less visible with water distributed to farms by underground pipe.
"You can't just take a dryland farm, put irrigation on and do the same thing. You have to rethink your whole farming operation to make it pay."
One-on-one meetings with farmers in stage two indicated that fewer would convert to dairy than some people suggested, said Goodfellow. It was estimated that once irrigated, former dryland farms would become a split of 40 per cent dairy, 40 per cent intensive arable and 20 per cent sheep, beef and other.
"Many farmers in stage two are interested in the intensive mixed arable system as it gives them flexibility. They have an arable background, and while they don't mind winter grazing, they don't want to milk cows."
When fully operational, the scheme will bring in 300 million cubic metres of alpine water into the catchment. As a result, 75m cubic metres of groundwater extraction will be switched off.
"That is a really key driver in enabling issues in the Selwyn-Waihora water management zone around groundwater over-allocation to be remedied." As well as restoring aquifers, CPW would also increase flows in lowland streams.
CPW holds the discharge consent for nitrogen allocation on behalf of farmers in the scheme. "It is a strict allocation and we will ensure farmers work within their nitrogen discharge limits. If farmers do not comply we have the ultimate ability to turn that water off.
"We have an extensive water quality monitoring programme. We have been doing that for two years and have only just started supplying irrigation water, so we have some good baseline figures."
A nitrogen allocation provided to CPW by Environment Canterbury was to develop new irrigation, not to intensify existing irrigation land use.
CPW has an allocation of 979 tonnes of nitrogen losses for its dryland farms. As the existing dryland baseline is 621 tonnes, this leaves an additional 358 tonnes to intensify farming operations under irrigation, about seven per cent of the total catchment load.
This equates to an average 36kg/ha of nitrogen loss a year, including dryland baseline, where farms are being converted from dryland to irrigation, with the upper limit set by good management guidelines modelling, not CPW.
Both existing and new irrigators across the Selwyn-Waihora zone will also have to demonstrate reductions in nitrogen losses from 2017 to 2022.
Rather than farming to numbers, farmers should seek further reductions in nitrogen losses by improving their management in terms of irrigation efficiency, fertiliser applications and stocking rate, Goodfellow said.
- Stuff
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