Switch to organic farming ‘would increase greenhouse gas’

A wholesale switch to organic farming would result in a net increase in greenhouse gas emissions – unless consumers radically changed their diets, a study has found.

Shifting 100% to organic production across England and Wales would reduce yields by as much as 40%, sucking in food imports to make up the shortfall, it suggests.

Published in the journal Nature Communications on Tuesday (22 October), the study was conducted by researchers at Cranfield, Reading and the Royal Agricultural universities.

See also: Top tips to achieve more resilient and sustainable soils

They said the increased imports would require more land use overseas, leading to a net increase in overall greenhouse gas emissions even though UK emissions would fall.

Food production

Organic farming produced fewer emissions, but also produced less food, said Adrian Williams, reader in agri-environmental systems at Cranfield University.

“We predict a drop in total food production of 40% under a fully organic farming regime – compared with conventional farming – if we keep to the same national diet,” he said.

“This results from lower crop yields, because yields are restricted by a lower supply of nitrogen, which is mainly from grass-legume leys within crop rotations or manure from cattle on pasture.”

The report say shifting to 100% organic farming in England and Wales would:

• increase beef cattle and sheep numbers, because of the increase in pasture. But the volume of meat would not increase because of slower production rates;
• decrease pig, poultry and egg production, because there would be less concentrated feed available;
• reduce dairy cattle numbers and milk production for similar reasons;
• increase production of potatoes, carrots, peas and beans; and
• decrease wheat production, with some crops, such as oilseeds, hardly grown at all.

Additional land

To offset the overall shortfall in domestic production, the study estimates that a fivefold increase would be needed in the area of overseas land producing food destined for England and Wales.

This additional land would probably be of sub-optimal quality and not as productive as the higher-quality land it replaced, said Laurence Smith, agroecologist at the Royal Agricultural University, Cirencester.

“A net reduction in greenhouse gases would only be achievable if accompanied by a major increase in organic yields or widespread changes to national diets,” Dr Smith said.

Organic farming initially involved higher carbon sequestration rates than conventional agriculture – a result of higher manure use and longer crop rotations – but this was limited to the first decade or two.

Soil would eventually reach a steady-state when carbon sequestration rates fell to zero, so UK organic farming would offset only a fraction of the higher emissions overseas.

The research concluded that net greenhouse emissions under a fully organic farming production method could increase by 21% over conventional farming baselines.

But this assumes that only half the extra overseas land would be converted from grassland, with emissions forecast to rise 170% once the carbon opportunity cost is factored in.