There is a paradox in plant nutrition: plants require nitrogen for growth, but while it is mostly found in the air (78% nitrogen, 21% oxygen), plants obtain it from the soil as nitrates (NO3) or ammonia (NH3), which can they absorb from humus and other organic matter such as harvest residue, manure, and compost, once they have been mineralised by bacteria.
In 1909 the German chemist Fritz Haber succeeded in combining atmospheric nitrogen with hydrogen to produce ammonia. He won the 1918 Nobel prize in chemistry for this work, which allowed the development of new fertilisers that made it possible to feed a world population that rose from 1.5 billion to more than 6 billion over the 20th century. A few bags of fertiliser were enough to provide all the nitrogen to grow crops and improve yields, doubling or tripling them. Farmers no longer needed to spread manure or compost, or cultivate nitrogen-rich leguminous plants.
The unlimited availability of cheap reactive nitrogen transformed agriculture, and by the 1960s chemical fertilisers were one of the four pillars of the ‘green revolution’, alongside high-yield crop varieties, pesticides and irrigation. The revolution was considered a great success, but in industrialised countries, and later in developing ones, massive use of synthetic nitrogen fertilisers produced unexpected results.
Once farmers had no need for solid or liquid manure, or for leguminous plants, they decided that breeding cows and sheep and letting them graze in fields was no longer worthwhile. Many got rid of their animals and produced only crops, mostly cereals. But milk and meat were still needed, and demand for them was growing rapidly, so other farmers specialised in livestock, and the most productive farms used industrial techniques, keeping animals indoors, and replacing fodder with cereal or oilseed-based feeds.
Thousand-cow farms
Within decades, European farming radically altered. In central and (...)
