Overall, large scale land use change will be needed, she said.
"In the long term the way in which food is grown, and the types of food grown, will have to change if biological emissions are to be reduced.''
Government has not asked farmers to offset agricultural emissions in the country's emissions trading scheme (ETS). The Green Party says farmers should be offsetting them, as industry does, because otherwise that burden will fall on ratepayers.
Federated Farmers is against including agriculture in the ETS, because it would make New Zealand farmers less competitive.
:We don't think the ETS is the appropriate tool for farming, but we will consider being involved in something else that makes more sense for farming,'' Federated Farmers climate change spokesman Anders Crofoot said.
Worldwide, agricultural gases make up 15 per cent of emissions. But New Zealand has an unusual emissions profile.
It's a First World country that has a profile similar to a Third World country, Mr Matthews says, because agriculture is "a fair chunk" of our exports.
The country's agricultural emissions are not increasing as fast as emissions from other sources, Dr Wright found. In the past 25 years road transport emissions have increased 71 per cent and industry emissions 45 per cent.
At the same time agricultural emissions increased only 15per cent - emissions efficiency against production has been improving about 1 per cent a year.
That's achieved by improving feed and nutrition, genetics, pasture management and animal health.
The main agricultural greenhouse gases are methane and nitrous oxide, Mr Matthews said. Millions has been spent on ways to reduce their emission.
Methane is emitted mainly by grazing animals burping, but also from swamps and landfills.
Mr Matthews said it represented a waste of energy that could have been converted to milk or meat. Instead the organisms in animals' stomachs convert New Zealand's rich, sweet grass into methane.
"Basically it's like a biogas digester inside the cow."
Scientists are looking for a vaccine that will kill the methane producing organisms.
They've found the organisms bounce back quickly, but are still looking.
Methane has turned out to be a less persistent greenhouse gas than was previously thought. It breaks down in the atmosphere twice as fast as carbon dioxide.
But nitrous oxide is is nearly 300 times more potent than carbon dioxide.
It's released by the action of microorgansims on fertiliser, manure and urine, and also from ploughed soils.
Adding dicyandiamide (DCD) to the soil via fertiliser can reduce the amount of nitrous oxide emitted. But the addition was stopped after traces of DCD were found in milk - it may not have been harmful, but consumers didn't like it being there.
To Mr Matthews the emission of nitrous oxide is also a waste.
"It's in our interest to put the right amount of fertiliser on at the right time, and lose none to water or the atmosphere."
He said farmland also stored carbon in scrub, forest and grassland - with less in grassland than in forest. Grassland storage hasn't been recognised in the ETS, which Mr Matthews said was a sore point with farmers.
The most obvious way for farmers to reduce their greenhouse gas emissions is to destock, but he said that wouldn't help the world situation.
"Production would be taken up by less efficient producers around the world and total greenhouse gases would actually increase."
There are other measures farmers can take. They can direct drill crop seed, rather than ploughing, to reduce nitrous oxide and carbon loss.
Mr Matthews said having more carbon dioxide in the atmosphere made plants grow faster. But farmers have a lot to lose from climate change.
His main worry is climate variability - more floods and more droughts.
"In the 33 to 34 years that I have been farming variability has got more extreme."
Whanganui's westerly winds usually bring enough rain, but the district can have autumn droughts.
Big rain events cause erosion.
On hill country planting poplars can hold the soil and suck up water, without restricting grazing.
Run-off can also be slowed by silt dams and wetlands. Tracks, fences and buildings can be sited to avoid damage from extreme weather.
In drought-prone areas plants like lucerne are enjoying a renaissance, popularised by Marlborough farmer Doug Avery.
Lucerne roots can get to 15m deep and pick up water unavailable on the surface.
The plants harvest nitrogen and provide high quality feed, but they need flattish land with a pH of 6.5 to 7 and careful harvesting.
Water can be stored at times of plenty, and held in farm ponds or larger regional dams and reservoirs, leaving enough to keep rivers healthy.
Farmers, especially dairy farmers, can offset their emissions by putting in their own woodlots or forestry or leaving marginal land in trees for permanent carbon storage.
Mānuka is a popular crop but doesn't store as much carbon as bigger forestry trees.
Mr Matthews is hoping research will continue and find the "silver bullet" solution for agricultural emissions.
"It's about producing livestock feed that grows in a challenging climate and produces less methane," he said.
FF Wellington senior policy adviser Jacob Haronga said farmers could be thinking about new crops in a warming climate - and they should think further than mānuka honey.
"I'm sick of people going on about mānuka honey. It's a volume game. It's a gold rush and there'll be a glut next."
Getting stock to the works faster and using feed pads would help reduce emissions. Farmers could also work on ways to quantify their emissions.
At present the only way of counting them is on the milk and meat sent to processors
It's a crude measure that doesn't take into account on-farm measures like dietary change or improved genetics.
Under current accounting farmers making such changes would be hit with the same charges as neighbours who were not, Mr Haronga said.
