LORD Melchett (Letters, March 2) seems to be indulging in a bout of wishful thinking on behalf of the Soil Association, backed up by dubious assertions.

While it may be theoretically possible to feed the world via extensive agriculture, this would require the universal adoption of a carefully-rationed vegetarian diet, with enormous areas of land given over to feeding the vast herds of animals whose manure would be essential for fertilisation.

I have no problems with so-called organic farming for those who can afford to indulge in intrinsically more expensive food offering no nutritional benefit. But organic food remains a marketing niche and, as has been said by others, its consumption is a lifestyle choice.

On the other hand, the area sown to genetically modified (GM) crops continues to grow year by year, as it has done since the mid-1990s, even though the full potential of the technology is far from being realised.

As for greenhouse gas emissions, those from farming are a small part of the total. Admittedly, the vital use of synthetic fertilisers is a significant user of energy, but it is biotechnology itself which holds the promise of developing plants which fix their own nitrogen from the air.

Martin Livermore,

Scientific Alliance, St John's Innovation Centre, Cowley Road, Cambridge.