Fertilizer, Down to A Science
Thursday, February 23, 2006
The garden will burst forth in a few weeks as the primal coaxing of longer days and warmer temperatures stirs winter's buds. We associate spring growth with the need to feed our plants, but speak of fertilizer and the debate divides sharply between strictly organic gardeners and those who see Miracle-Gro and its ilk as the key to vigorous and free-flowering plants.
The proliferation of commercially produced organic products -- from stinky fish emulsion to processed chicken manure -- suggests a mainstream embrace of gardening philosophies once considered far out. However, petrochemical fertilizers dominate, especially in the broad context of world agriculture, and demand for them grows each year.
Whichever side of the line you're on, or even if you straddle it, the story of modern fertilizer production is fascinating, not least because the origin of so common a product is so little known.
"People don't even know where food comes from, let alone the nutrients to grow them or how they are made," said Harriet Wegmeyer, a spokeswoman for the Fertilizer Institute, a Washington-based industry lobbyist.
The three major nutrients -- nitrogen, phosphorus and potassium -- bestow different benefits on plants. Nitrogen aids vigorous vegetative growth, phosphorus is needed for root growth and vigor, and potassium helps increase plant metabolism and disease resistance.
Nitrogen is the king of the hill. The world needs roughly 110 million tons of it annually, along with 33 million tons of phosphorus and 30 million tons of potassium, said Christine Gillespie, a spokeswoman for one of the world's largest manufacturers, Calgary-based Agrium Inc.
The nitrogen production is based on a process developed almost a century ago by German scientist Fritz Haber. The world was facing a shortage of nitrate fertilizer with the industrialization of agriculture in the late 19th century. Scientists knew the air we breathe is a sea of nitrogen, but it took Haber to invent an effective way of extracting it. Into a heated, pressurized canister containing a catalyst, he injected hydrogen and nitrogen at one end and extracted ammonia at the other.
The same principle is employed today, using natural gas both as a fuel and for its component hydrogen, mixed with air over a catalyst in a chamber that is pressurized and heated. The resulting ammonia gas is chilled into a liquid. This, in turn, is processed further into a number of different nitrogen fertilizers, including urea, nitric acid, ammonium nitrate, and a combination of urea and ammonium nitrate, which is blended with water to produce liquid nitrogen fertilizer. One of the most common forms of nitrogen in agriculture, especially in the Great Plains, is anhydrous ammonia, which is a liquid under pressure and injected into the soil. Agrium Inc. and some other manufacturers have stopped selling ammonium nitrate as a fertilizer because of the security issues and regulations now controlling its distribution. It can be made to explode, and was used by Timothy McVeigh in the 1995 Oklahoma City bombing.
The air is free, but extracting nitrogen from it is not. The process uses large amounts of natural gas, which rose sharply in price last year. It spiked to more than $14 per million British thermal units in December but is now down to about half that. Still, it is historically high, and the result of the rise has been temporary and permanent closings of North American plants and a large increase in imported fertilizer, up from around 30 percent to 50 percent from countries where gas costs are lower.
Haber's invention changed the world. First, it prolonged World War I by giving Germany the explosives it needed to wage war; but it also allowed food to be grown on a massive scale and is directly linked to another explosion, that of the population of the planet.
The continued demand for chemical fertilizer is fueled not just by a net increase of 75 million people per year, but the fact that the inhabitants of large developing countries such as China and India are switching to diets higher in meats. This takes more grain to feed poultry, swine and cattle, and more fertilizer to grow grain.
Gillespie said few people realize that synthetic fertilizers are "chemically identical" to organic fertilizers. "I think people think because it is so involved a process it must be harmful, and that's not the case." Well, not quite. Even fertilizer companies acknowledge that the careless use of fertilizer can bring environmental damage by causing algae to grow, depleting rivers and estuaries of life-giving oxygen. Animal manure, too, contributes to the pollution.
But what of the gardener?
Organic growers argue that chemical fertilizers do not build the soil, unlike organic fertilizers and nutrient-rich compost that improve the soil's structure and spawn microbial life. The bacteria and fungi that thrive in such soils enhance the ability of a plant to extract nutrients from the soil and at an even rate, said Patricia Millner, a soil scientist with the Agricultural Research Service in Beltsville. "Studies here and elsewhere show you can reduce the input of chemically synthetic fertilizers by up to one-third in some cases because of the synergies obtained when you increase the organic matter and natural nutrient cycling in soils," she said.
Still, Gillespie said, chemical fertilizers are loaded with nutrients and can be blended to provide precise levels of nitrogen, phosphorus and potassium in a way that organic fertilizers cannot. Ammonia contains 82 percent nitrogen, she said, and some animal manures just 3 percent.
To sustain the expanding human race without it, she said, would mean a world where much more forest would be given over to crop cultivation, and a planet awash in animal manure.