杏吧原创

NUMEROUS ancient civilisations crashed when their soils turned to dust under sustained cultivation. Not China. The Chinese have been farming their fields intensively for 4000 years. What did they do right?

The answer is night soil, says David Montgomery. They recycled the soil鈥檚 nutrients by spreading their excrement liberally across the land. After good harvests, farming communities deliberately stuffed themselves with extra helpings of rice in order to 鈥渞einvest in their stock of natural capital鈥� and replenish the soil.

In the same mould as Jared Diamond鈥檚 Collapse, Montgomery鈥檚 Dirt: The erosion of civilizations is a compelling study on soil: why we need it, how we have used and abused it, how we can protect it, and what happens when we let it slip through our fingers.

The Mesopotamians, the Mayans, the Greeks and the Romans 鈥� possibly even the 20th-century Russian empire 鈥� all lost their grip when they lost respect for their soil. Other societies came up with smarter solutions to soil problems. Before Europeans invaded, the people of the Amazon fed large cities in the jungle by enriching their thin natural soils with urban compost. More recently, Cubans have gone organic, saving their soils and food supplies in the process, while next door Haiti has stripped its soils bare and suffered the consequences.

The history of soil is both rich and surprising. The state of soils played a part in the American civil war, and the pursuit of the fertiliser guano helped drive European countries鈥� global conquests in the 19th century. Then Europe swapped guano for chemicals. During the first world war the Germans diverted so much of their nitrate-manufacturing capacity from fertiliser to explosives that 鈥渋n the end, the German military did not so much run out of ammunition as it ran out of food鈥�.

Of course there have also been advances in our understanding of soil conservation. For example, the book revives the reputation of Charles Darwin鈥檚 last work, on the effect of earthworms on soil, which these days is often dismissed as the ramblings of an old man. Montgomery also shows reverence for Walter Lowdermilk and other key figures who toured the world analysing soil erosion after the shock of the US dust bowl in the 1930s.

Soil erosion is a natural process, but on average humans have increased erosion rates tenfold. As testimony, Montgomery points to parts of the US Midwest where the native prairie 鈥渞ises six feet above neighbouring ploughed fields鈥�.

Who is to blame for today鈥檚 diminishing soil supply? Montgomery points the finger at modern agribusiness. It is received wisdom that the world is only able to feed its exploding population thanks to the green revolution, which was driven by new high-yield hybrid crop varieties that require huge doses of fertiliser and irrigation water. And yet, he points out, the biggest strides against hunger were made in communist China, which was 鈥渂eyond the reach of the green revolution鈥�. It fed its people through land reform, he says.

Land reform is controversial, as it involves enforced redistribution, but clearly something must be done. The downside of the green revolution and the virtues of organic, no-till farming become evident through Montgomery鈥檚 historical analysis. If we think we can do without soil, we might see our own civilisation collapse.

We need to act quickly. In the coming years, agriculture will not only suffer the effects of global warming, it will also contribute to it. Agriculture consumes 30 per cent of our oil, Montgomery reminds us, mostly through the manufacture of fertiliser. Ploughing the world鈥檚 fields is releasing large amounts of carbon from the soil into the atmosphere. We could, he argues, grow as much food by doing without most of the fertilisers, and soak up a quarter of our industrial carbon dioxide emissions through reduced ploughing. It鈥檚 a compelling manifesto.

鈥淧loughing releases large amounts of carbon into the air鈥�