A group of leading soil scientists say there have been significant changes in soil carbon levels on farms.
The scientists are part of a research initiative on the sustainable management and use of soil resources, in a collaboration between the crown research institutes Plant and Food, AgResearch and Landcare.
They say a number of lowland dairying properties have lost carbon over the last 20 years, but hill country farms have, surprisingly, gained carbon in their soils.
Programme leader Dr Brent Clothier from Plant and Food says some changes are contrary to what scientists had thought would happen, so they are trying to understand the mechanism behind the changes.
Dr Clothier says nearly one fifth of the country's gross domestic product (GDP) relies on the top 15 centimetres of its soil and carbon is an essential element.