Growing pains: Scientists paint troubling picture for NZ’s crucial farm pastures

• Productive pastures are critical for agricultural sectors that collectively generate nearly $40 billion each year – or just under half of New Zealand’s total annual exports.
• But a just-published review finds productivity gains of the boom-time 1990s and early 2000s have slowed to a crawl, with climate change impacts now mounting.
• The study’s authors say more research is urgently needed to understand what’s driving the decline, as well as new tech to help farmers adapt to a warming world.

They’re the backbone of our backbone industry: but productivity gains in New Zealand’s plentiful farm pastures have now stalled, or even declined, scientists report.

A troubling new review also examines how climate change impacts are having a worsening impact on base grass growth around the country – and that gene-modification (GM) tech will be needed to help farmers adapt.

Long New Zealand’s number-one agricultural crop, pasture supports sectors which collectively generate $38b each year – that’s just under half of our total annual exports of goods and services – while providing some 80,000 jobs.

Throughout the “white gold rush” dairy boom of the 1990s and early 2000s, farmers reaped productivity gains using better pasture management and fertiliser with higher nitrogen levels.

Long New Zealand’s number-one agricultural crop, pasture supports sectors which collectively generate $38 billion each year. Photo / Bevan Conley

But those gains have since slowed to a crawl.

The yearly increase of pasture eaten on dairy farms stood at just around 0.26%, compared with 1.48% before 2001/02.

“Many farms may have reached the peak pasture yields possible within the climatic environment of the late 20th century,” found the review, just published in the New Zealand Journal of Agricultural Research.

Many dairy farms may have already optimised critical factors like grazing management and pest control, while reaching or exceeding their optimal range of soil phosphorus levels.

For these farms, simply adding more fertiliser or increasing livestock numbers no longer boosted productivity.

The researchers found the same plateauing effect has been emerging among sheep and beef farms.

And, in northern regions particularly, farmers were feeling the strain of hotter, drier summers and more extreme weather events brought on by a warming world.

Here, such effects were thought to be already offsetting climate change’s “positives” for grass growth – like mild warming and higher carbon dioxide (CO2) levels – while limiting the benefits of more nutrient inputs.

In the Far North, pasture productivity had declined significantly over the past two decades, despite the predicted benefits of rising CO2 levels.

Instead, local farmers were dealing with droughts, heatwaves and shifting seasons that were making it harder to keep pastures healthy.

Dry conditions in Kaikohe, Northland, as pictured in February 2020. Photo / Chris Tarpey

“To paraphrase, the plant is facing more unfavourable growing days each year, because it is too hot, dry or wet,” study co-author and AgResearch principal scientist Dr Alec Mackay told the Herald.

On top of that, climate change was expected to worsen problems with pest insects, weed growth and animal diseases.

Despite these shifts and increasing threats, Mackay and his colleagues pointed out major knowledge gaps remained, such as what impact new grass cultivars had made in slowing the trend.

“Our pasture provides a competitive advantage to New Zealand that supports billions of dollars in export revenue – and any decline in that pasture growth over time is something we need to take seriously,” he said.

“We need to understand more about the underlying factors and mechanisms contributing to the decline to help us develop technologies and strategies that target future productivity gains.”

Mackay and his co-authors also argued it would be “implausible” that New Zealand could meet future challenges through forage breeding without access to GM tech.

AgResearch and its partners had already been investigating the potential of modified pasture – such as HME ryegrass – but New Zealand’s tight GM regulations meant much of this work had been restricted to specialised containment glasshouses, or field trials overseas.

“However, the recent introduction of the Gene Technology Bill to Parliament means that the regulatory environment may soon change and allow for more outdoor trialling and use of modified pasture in real-world conditions,” Mackay said.

DairyNZ, also involved in the new review, said a “comprehensive look” was needed regarding the issues raised by the researchers.

“This research is important because pasture-based farming sets us apart internationally and is the base of our cost-competitiveness,” DairyNZ general manager of research and science Bridget Maclean said.

“We need pastures that remain resilient in a changing climate.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

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