There are calls for productive soils to be protected for future generations.

A new report - Our Land 2018 - highlights the danger of urban sprawl, saying it's taking up New Zealand's most productive land.

Urban planning expert Bryce Julyan told Mike Hosking some of the most productive rural land is very close to urban centres.

"Some of those soils, particularly in South Auckland, around Pukekohe are very highly productive they are very rare soils."

He warns vegetable prices could go up for city dwellers if urban sprawl continues.

"If you are saying we are going to use this soil or this land for housing and our potatoes have to be grown now much further away, the result of that is that you are going to pay a lot more."

LISTEN ABOVE AS BRYCE JULYAN TALKS TO MIKE HOSKING