Issue link: http://winesandvines.uberflip.com/i/998810
BOOK EXCERPT 50 WINES&VINES July 2018 F or much of human history, the role of organic matter in soil fertility was no secret. Farmers and philosophers alike believed that humus — soil organic matter — nourished plants. Until, that is, two key discoveries undercut this long-held belief. The first was the discovery of photosynthesis — that plants obtained their carbon, and thus most of their mass, from the air and not the soil. The second was the observation that most humus was insoluble and could not be sucked up by plant roots. So soil organic matter did not feed plants. What replaced the humus theory was the idea of the soil as a chemical reservoir from which plants drew sustenance. In the first half of the 19th century, German chemist Justus von Liebig demonstrated that a lack of avail- ability of key nutrients could limit plant growth. He also established that adding ele- ments in relatively short supply dramatically boosted plant growth. Farmers working de- graded fields found that adding calcium, phos- phorus, or potassium could bring crop yields back up to levels not seen since their grandfa- ther's day. So did the addition of nitrate- and phos- phate-rich guano, bird droppings that were aggressively mined from South Pacific islands. As the supply began to run low in the late 19th century, European and North American crop yields were threatened due to centuries of soil loss and degradation. Getting enough nitrogen to crops became a top priority. Nitrogen gas (N 2 ) bathes our world — it makes up almost 80% of Earth's atmosphere. So you might think that plants could grab all the nitrogen they need from the air. That's what they do for carbon through photosynthe- sis. But the triple bond between the two atoms in a molecule of nitrogen gas is incredibly stable. While nitrogen is essential for making amino acids, proteins, and DNA, not much of it is biologically available. This means that nitrogen is often the limiting element for plant growth — especially in soils with little organic matter. But there was another strategic motivation for securing a steady supply of nitrogen: it was essential for making high explosives. In 1909, a pair of German chemists — Fritz Haber and Carl Bosch — figured out how to synthesize ammonia (NH 3 ). Using hydrogen gas as a feedstock, they developed a high-pressure, catalyst-based process that worked at high temperatures. The ability to manufacture ni- trogen both prolonged the nightmare of the First World War and produced the miracle of cheap fertilizers that could boost crop yields on degraded land, of which there was no shortage. After the war the Allies demanded the se- cret to the Haber-Bosch process so they could modernize their own munitions factories. Decades later, after the Second World War, the same Allied countries converted idled muni- tions factories to fertilizer production, a change that could have been quickly reversed had the Cold War heated up. The widespread avail- ability of cheap fertilizers, coupled with the new fertilizer-loving wheat and rice varieties of the Green Revolution, doubled global crop production. Growing a Revolution An excerpt from a book that examines the roots of the underground economy and how to improve soil health By David R. Montgomery KEY POINTS Most conventional thinking on soil is rooted in a soil chemistry perspective. Advances in soil ecology and microbiology offer new perspectives on soil fertility and plant nutrition. Cultivating beneficial soil life can build healthy soils that support crop health. EDITOR'S NOTE Growing a Revolution, Bringing our Soil Back to Life introduces the reader to farmers around the world at the heart of a brewing soil health revolu- tion that could bring humanity's ailing soil back to life remarkably fast. It is available from books.wwnorton. com. The following excerpt draws on visits to farms in the industrialized world and developing world to show that a new combination of farming practices can deliver innovative, cost- effective solutions to the problem of soil degradation. The author's hands showing khaki colored, low-carbon soil (left) from his yard prior to his wife restoring soil organic matter to build a garden with dark brown, carbon-rich soil (right).