Green Party co-leader Russel Norman had to explain his party's opposition to land farming in Taranaki, when he appeared at the Federated Farmers National Council meeting.
It was one of a number of issues farmers debated with him.
Land farming is the term used to describe the process of spreading the spoil from oil and gas drilling on farm land.
A report by soil scientist Dr Doug Edmeades, commissioned by the Taranaki Regional Council, found the practice, combined with irrigation and fertiliser, produces high quality pasture that can increase the value of marginal land tenfold.
Dr Norman was asked why, in view of that, the Green Party continues to oppose land farming.
"What was interesting about Doug's report was that the level of hydrocarbons in the soil on those farms is currently above the level it needs to be to achieve the resource consent when it's released from its land farming activities and I think that's a bit concerning.
"I don't think that our consumers, if you think of parents feeding their children infant formula are going to take very kindly to that kind of product."
Mr Norman was told that the hydrocarbon levels weren't a problem because they dissipated with time and farmers could still have the production gains.
But he pointed out that Fonterra is having to send milk samples from those farms for testing in Australia, to check for hydrocarbon contamination.