A new breakthrough could help prevent excess nitrogen left in soils and waterways by farm fertilisers from becoming a harmful greenhouse gas, New Zealand and US scientists say.

Currently, agriculture, primarily through its use of fertilisers, contributes more harmful nitrous oxide greenhouse gas to the atmosphere than any other sector in the world.

The damaging nitrous oxide gas is 300 times more effective at trapping heat in the atmosphere than carbon dioxide and 10 times more effective than methane.

It also moves into the stratosphere and destroys ozone.

The scientists hope their research can unlock new ways of manipulating the natural nitrogen cycle in soils so that excess and inorganic forms of nitrogen can be converted to an unreactive di-nitrogen gas rather than nitrous oxide.

Di-nitrogen gas makes up 78 per cent of our atmosphere and is not a greenhouse gas contributing to global warming.

The international team's breakthrough came when they discovered a way under standard temperature and pressure conditions of chemically combining naturally occurring nitrogen with inorganic nitrogen, commonly left behind by fertilisers, into di-nitrogen.

They hope the reaction can in the future be organically recreated in soils with the help of plants and fungi.