The Rational Optimist (P.S.)

by Matt Ridley

Politicians can make my prediction fail. Should the world decide to go organic – that is, should farming get its nitrogen from plants and fish rather than direct from the air using factories and fossil fuels – then many of the nine billion will starve and all rainforests will be cut down. Yes, I wrote ‘all’. Organic farming is low-yield, whether you like it or not. The reason for this is simple chemistry. Since organic farming eschews all synthetic fertiliser, it exhausts the mineral nutrients in the soil – especially phosphorus and potassium, but eventually also sulphur, calcium and manganese. It gets round this problem by adding crushed rock or squashed fish to the soil. These have to be mined or netted. Its main problem, though, is nitrogen deficiency, which it can reverse by growing legumes (clover, alfalfa or beans), which fix nitrogen from the air, and either ploughing them into the soil or feeding them to cattle whose manure is then ploughed into the soil. With such help a particular organic plot can match non-organic yields, but only by using extra land elsewhere to grow the legumes and feed the cattle, effectively doubling the area under the plough. Conventional farming, by contrast, gets its nitrogen from what are in effect point sources – factories, which fix it from the air.