Last week Greenpeace released a campaign to "ban synthetic nitrogen fertiliser and save New Zealand's rivers."

"Synthetic nitrogen fertiliser is the fuel that drives industrial dairying. It's spread on to New Zealand dairy farms to grow more grass for too many cows", said Greenpeace campaigner Gen Toop.

Leading farming academic Dr Jacqueline Rowarth disagrees, saying Toop's statement refers to a way of farming that doesn't occur in New Zealand.

"She's saying it's driving industrial dairying, which actually we don't have in New Zealand," Rowarth told The Country's Jamie Mackay.

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"Industrial is when you have very high densities and they're inside and they're feeding grain - it's the American system fundamentally."

Toop advocates for New Zealand agriculture to move to a regenerative system which Rowarth likens to animals grazing on the "great savannahs".

Here Rowarth says the natural cycle is for animals to move in mobs and "trample in their dung and their urine and they move on and they come back when the grass has grown again."

"Well in the savannah, that might be a year. In New Zealand - whether you have nitrogen added or not - you're probably going to be back within three to six weeks. Because the grass grows in our environment.

"So ... we already are doing what Greenpeace is advocating - but she doesn't see that."

To feed a hungry planet, Rowarth says agriculture needs modern technologies "and that does include nitrogen, used carefully."

Also in today's interview: Dr Jacqueline Rowarth looks in to the issues with N leaching in horticulture.