Organic farming uses less pesticides, fertilisers and herbicides than non-organic practices, and organic-farming advocates also claim it saves water and controls erosion.

Key points: Organic food crops mostly produce less CO2 emissions, but they also have smaller yields

Organic food crops mostly produce less CO2 emissions, but they also have smaller yields Making up the difference in yield pushes organic emissions above non-organic

Making up the difference in yield pushes organic emissions above non-organic Reducing meat consumption could have bigger emissions savings than farming methods

But converting the world's agriculture to organic would actually produce far more carbon dioxide emissions, according to a new study.

In a scenario in which England and Wales hypothetically switched to 100 per cent organic farming practices, researchers found organic methods typically had much lower nitrous oxide and carbon dioxide emissions per unit of area farmed, thanks to the use of nitrogen-fixing plants rather than fertilisers.

Soil-carbon sequestration was also higher in organic crops, compared to non-organic.

But the volume of food grown per unit of area farmed organically was 40 per cent less than yields from conventional farming methods, according to the research, published in the journal Nature Communications today.

The green and purple bars illustrate the increased land area outside England and Wales needed to produce food under the organic model. ( Supplied: Nature Communications )

The emissions savings by farming organically were not enough to offset the reduced productivity, said study lead author Guy Kirk from Cranfield University.

"Organic farming necessarily requires more land to produce a given quantity of food," Professor Kirk said.

This is because of the need to plant legumes in between crops to fix nitrogen in the soil instead of using fertilisers.

While there is a popular perception that organic farming is more environmentally friendly on all fronts, the findings weren't at all surprising, according to climate and primary industries expert Richard Eckard from the University of Melbourne.

"[It's] logical, a fair assessment, and what I would expect," Professor Eckard said.

"There's a strong line of thinking, certainly in the area I'm working in, that says that consequences have to be taken into account.

"If everyone went organic, probably though there would be less environment impacts [from industrial agriculture], we wouldn't produce a fraction of the food we can now."

Reducing meat could have bigger emissions savings

Cutting down on meat would make a bigger difference to emissions than between organic and non-organic cropping. ( Supplied: Terry O'Leary )

Although the overall trend was that organic foods resulted in greater greenhouse gas emissions, on a food-by-food basis there is more nuance.

Things like cabbages, wheat and rye produced less greenhouse gas when grown organically than otherwise.

Instead of a blanket approach to farming practices, they need to be tailored to specific crops and environments, Professor Kirk said.

"There are certainly benefits to organic approaches, such as for soil fertility and less pesticides," he said.

"We need some mix of the best aspects of organic and conventional methods."

The scope of the study specifically looked at emissions, and didn't take into account other environmental impacts of agriculture.

Recent research has linked pesticide use in non-organic agriculture to the collapse of insect and bird populations, for instance.

And fertiliser-intensive farming has also been shown to contribute to algal blooms on stressed river systems.

But while some emissions reduction may be achieved by switching between organic and non-organic farming methods, bigger gains can be made by wholesale dietary change, the authors state.

"Given the much larger contribution of livestock farming to greenhouse gas emissions, a greater impact could be gained from reduced meat consumption," they state in the paper.

This is especially true in places like Australia, where our consumption of red meat is well above the global average.

In Australia, agriculture contributes about 14 per cent of our total emissions. More than 70 per cent of that comes from livestock.

And livestock is a high contributor of methane gas, which is more potent than CO2 in terms of warming potential, Professor Kirk said.

"Producing meat requires more land per food calorie than crops, and ruminants produce methane which per molecule has over 20 times the global warming effect of CO2."