Land fertility

To answer Carolyn Taylor 
(Letters, 24 March), in 2009, the Soil Association solicited Reading University to compare yields on 180 matched organic and 180 conventional farms.

The wheat yield per organic farm was only 33 per cent that of the conventional farms.

Organic regulations ban the use of external nitrogen, necessary for plant growth. Instead, organic fields are sown with grass and clover, a legume.

After several years these are ploughed in and used to grow crops for a few years. Productive land is used up for years in a fertility building exercise while conventional farms sensibly use mineral fertiliser throughout.

Organic yields per farm and thus land area will always be disadvantaged and remain poor. The maximum legume yield of nitrogen is known and in an organic world could feed no more than three billion, leaving four billion to starve.

The UN publication made much of by May East and Carolyn Taylor is the proceedings of a conference of like-minded organic people.

It does not represent majority agricultural or UN opinion on mankind’s future.

No-till (conservation) agriculture maintains soil structure, yield, wildlife, stops erosion, and its emissions are one third that of organic farms.

With new technology it is currently the best option.

Having spent a lifetime trying to get students and the public to adopt critical approaches to public policy, it is equally offensive to me to find uncritical opinions touted as a panacea to serious future population and food problems.

(Prof) Tony Trewavas FRS FRSE

Scientific Alliance 
Scotland

North St David Street

Edinburgh