The return of Eco-N for use on New Zealand pastures would be a boon for farmers and efforts to protect waterways, Federated Farmers environment spokesperson Chris Allen says.

Feds strongly supported any such move, Allen said.

"It deserves a 'grown-up' conversation around the issues involved because Eco-N is a valuable tool that enables farmers to temporarily store nitrogen in soil when it would otherwise be vulnerable to loss — a bonus both for agri-business productivity and to reduce nitrate leaching into waterways.

"It's also one of the answers on the pressing issue of reducing nitrous oxide emissions," he said.

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Federated Farmers said in a statement Eco-N was a trademarked nitrification inhibitor product developed by Lincoln University in partnership with Ravensdown Fertiliser Co-op Ltd. It was launched in New Zealand in 2004.

Read more from Federated Farmers here.

Farmers found they could typically achieve an extra $600/ha in profit from milk production while also substantially reducing nitrate leaching losses and emissions of NO2 into the atmosphere.

But Eco-N was taken off the market after minute residues of the active component Dicyandiamide (DCD) were found in milk powder.

It was never a food safety issue (DCD is regarded as safe), but as there was no international agreement about acceptable limits, Eco-N was withdrawn to avert possible trade repercussions, Federated Farmers said.

Fertilisers containing DCD have continued to be used by farmers in the United States, Federated Farmers said.

Ravensdown said there was now a chance that world regulatory authorities, including New Zealand's Ministry for Primary Industries, might ratify an umbrella codex agreement mid-2019 to set rules for a maximum residual level for a range of benign compounds in food products, Federated Farmers said.

If that happened, Eco-N could be back in use here during autumn to winter 2020.

"We should let the science speak, and that should guide the international discussions on this — and the stance of food processors, marketers and dairy companies should codex agreement be reached," Allen said.

"We all need more tools in our toolbox as we chase the productivity gains needed to feed ever-growing and hungry populations, while also meeting the imperative to enhance water quality in our groundwater, rivers and lakes."