New research suggests the environmental impact of sheep and beef farming in New Zealand has remained steady over the past 20 years despite a big increase in productivity.
AgResearch scientist Dr Alec MacKay has compared sheep and beef farm inputs - livestock and fertiliser - with the outputs of meat, greenhouse gases and nutrients.
Dr MacKay said he found huge eco-efficiency gains.
For instance, he says, in hard hill country there has been an almost 50% rise in saleable product over the last 20 years.
And along with this there has been 20% reduction in nitrate leaching per kilogram of product sold over that time, and a 40% decrease in greenhouse gas emissions per kilogram.
"There's been no absolute decrease in the amount of nitrate leached but more importantly there's been no significant increase"
Dr MacKay says production gains have been made through a higher number of lambs produced per ewe, and increased growth rates.