Organic potatoes have the same carbon footprint as conventionally grown varieties, shows an assessment by supermarket Tesco.
They could be lower still if the carbon store in the soil is taken into account, says the Soil Association, the leading certifier of organic products in the UK and a supporter of environmentally friendly food production.
The findings come as the Soil Association, the leading certifier of organic foods in the UK, comes under criticism for plans to make its label subject to environmental criteria. The retail chain, the Co-op, said recently that the certification would be too difficult for developing world farmers to meet.
But information on Tesco's new carbon footprint labels, being introduced today, suggest that organic products may anyway be more environmentally friendly than others.
Tesco's labels, which will be added to its 20 of its own-label laundry detergents, orange juice, light bulbs and potatoes, show a figure that measures the total emissions of greenhouse gases during the production, distribution, storage and use of the products.
Its labels show virtually identical carbon footprints for organic and conventional potatoes. Organic potatoes generated 160g of CO2 emissions per unit, the same as King Edwards conventionally grown potatoes. Both organic baby new potatoes and Anglian baby new potatoes generated 140g of CO2e.
However Tesco's researchers said that they were not able to take into account the amount of carbon that can be stored or released from agricultural soils by different farming practices.
Organic farming is said to store carbon in the soil and use less fossil fuel energy, lowering the carbon footprint of organic products.
Long-term trials cited by the Soil Association show that organic farming adds between 100-400kg in extra carbon per hectare to the soil each year, compared to non-organic farming.
When this stored carbon is included in the carbon footprint of organic food, it reduces the total greenhouse gas emissions by between 25-75 per cent.
"Given this omission, the Tesco findings for the carbon footprint for organic potatoes and tomatoes are particularly positive," said a Soil Association statement.
Tesco noted however that in the cultivation stage of organic potatoes, "the saving from using organic fertilizer is balanced out by increased emissions from irrigation."
In another study on tomatoes, which will not be labeled in Tesco's stores yet as they are not in season, organic tomatoes had a comparable carbon footprint to conventionally grown varieties too.
"There is a balance between reduced fertilizer use but lower yields and significant quantities of compost used."
Peter Melchett, policy director at the organization, said: "We congratulate Tesco for making an important start in helping people to reduce the impact of their food on the climate - something the government has so far failed to do."
Tesco's Carbon Reduction Label has been developed by the UK-based Carbon Trust organisation. Other companies are expected to follow its move in the near future.