To rebuild topsoil, organic farmers plant green manures, make compost and undersow crops with clover to increase organic matter (humus) in soil. The result is better water retention and soil fertility. Conventional agriculture loses arable land every year. One cause is salination: chemical fertilisers destroy humus so that frequent irrigation is needed, water retention is minimal and salts build up. This canÔ´ be sustained. Building humus also captures and stores carbon, thus reducing global warming. Organic farmers who plough only occasionally and use green manures can accumulate up to one tonne of carbon per hectare per year. Organic farming also uses less fossil fuel, preferring human labour to heavy machinery. Fertilisers and pesticides are made from fossil fuels, too; organic farmers use less of them.
The arithmetic of farming can appear ludicrous: it takes 12 calories of fossil fuels to produce one calorie of food grain in industrial agriculture. Organic farming uses five calories. Organic arable production can be 35 per cent more energy efficient, and organic dairy production 74 per cent more efficient than non-organic production. Worldwide, farmers now use 10 times more fertiliser and spend 17 times more on pesticides as in 1950. The share of the harvest lost to pests, however, is unchanged.
