Synthetic Fertilizers - Environmental Risks
The case against synthetic fertilizers
Industrial process opens door to many
environmental risks
- Deborah K. Rich
It doesn't get much more natural than nitrogen. Nitrogen gas (N2) spewed forth from the bowels of hot young planet Earth 5 billion years ago to become a defining element of the atmosphere. Nitrogen comprises 78 percent of the gasses that swirl invisibly around us and permeates our very essence.
Nitrogen is a part of all living cells. It is a building block of amino acids and nucleic acids, the stuff of proteins and genes. Nitrogen is essential to metabolic processes involved in the synthesis and transfer of energy. It is a part of chlorophyll, the green pigment in plants that enables photosynthesis. Nitrogen speeds plant growth, increases seed and fruit production, and improves the quality of leaf and forage crops.
But it is its very nature that caused the National Organic Program to ban most forms of nitrogen fertilizer from use on certified organic farms, deeming it unsustainable and damaging to the environment.
The reason why stems from a quirk of evolution. Life emerged and refined itself beneath a canopy of nitrogen gas, yet few organisms can secure the nitrogen they need for healthy growth from the atmosphere.
Triple chemical bonds between the two atoms of the gaseous N2 molecule render atmospheric nitrogen inert or incapable of linking with atoms of other elements; nitrogen gas simply does not participate in any chemical reactions at room temperature or even at the higher temperatures found in small fires. Before life can make use of atmospheric nitrogen it must be "fixed" (a rather confusing term for the process of breaking nitrogen atoms apart) so that the nitrogen atoms can combine with atoms of different elements.
Only two natural phenomena can make the fix: lightning and bacteria. Lightning's powerful flashes cleave the bonds of nitrogen molecules in the surrounding air. Set free, the nitrogen atoms combine with oxygen and rain upon the Earth as nitrates (NO3-) -- a form of nitrogen that plants can absorb. Lightning contributes about 10 million metric tons of total fixed nitrogen per year for use by plants and animals.
A few types of bacteria generate enough energy by oxidizing or "burning" carbohydrates to fix atmospheric nitrogen as well. The most familiar of these is rhizobium, which forms symbiotic relationships with members of the legume plant family. The bacteria convert molecules of nitrogen trapped in air pockets in the soil into ammonia (NH3), which other types of bacteria then convert into nitrates. Scientists estimate that microorganisms add approximately 140 million metric tons of fixed nitrogen to the soil every year.
Once fixed nitrogen has been taken up by plant roots, it can pass up the food chain to animals until it returns to the soil embedded in excretions and dead plant and animal material. Bacteria will decompose the fallen organic materials and recycle the nitrogen back to nitrate form for reuse by plants. In the process, some of the nitrogen will be converted into nitrogen gas and return to the atmosphere, completing the cycle from atmosphere to soil and back again.
Until the 20th century, farmers seeking to provide sufficient nitrogen to their crops dug cover crops, manures or compost into their soils and relied upon soil microbes to make the nitrogen in these materials available to plants' roots.
Then, in 1909, German physical chemist Fritz Haber developed a high-temperature, high-pressure process to fix atmospheric nitrogen in his lab. Another German chemist, Carl Bosch, soon expanded Haber's process to a factory scale. Known as the Haber-Bosch process, industrial fixation of nitrogen combines atmospheric nitrogen and hydrogen into ammonia, the basis for all synthetic nitrogen fertilizers. Natural gas is most often the source of the hydrogen.
Imagine the power now vested in humankind. With the ability to fix our own nitrogen we could free ourselves from dependence upon lightning and microbial masses and ramp up agricultural productivity to feed a hungry world. Perhaps the human species could yet outwit the Malthusian math that predicted that population growth would always outstrip our ability to increase food production. Indeed, so marvelous was this alchemy that both Haber and Bosch were awarded the Nobel Prize for chemistry.
Imagine now, just a little less than 100 years later and as world hunger continues to rise, asking farmers to stop using industrially fixed nitrogen. It's a wonder that the organic movement ever got off the ground.
The National Organics Program, which regulates the use of the organic label in the United States, prohibits the use of synthetic substances unless their use is specifically allowed via exemption, an exemption not granted for synthetic nitrogen fertilizer.
The reasons why are of such import that they alone should set off a stampede to the nearest organic farmer's market.
Reason No. 1 is that synthetic nitrogen fertilizers are not sustainable. Building an agricultural system based upon industrially fixed nitrogen makes our ability to feed ourselves dependent upon a non-renewable fossil fuel and upon the wisdom, benevolence and cooperation of heads of state and multinational petroleum companies.
Remember that natural gas is a key component of the Haber-Bosch process and accounts for 70 to 90 percent of the cost of nitrogen fertilizer production. Natural gas is found either dissolved in crude oil, or as a gas cap above reservoirs of oil. Due to the high cost of shipping natural gas, fertilizer plants are located where the gas is relatively abundant and cheap. Venezuela, Trinidad and Argentina are big producers. So are Russia, China and the Persian Gulf countries. According to the Fertilizer Institute, the United States was the largest importer of nitrogen fertilizers in 2002, importing 6.6 million metric tons of nitrogen or slightly over half of its total nitrogen fertilizer needs (approximately 12 million tons per year).
Synthetic nitrogen fertilizers also fail to pass muster because of the environmental damage done when we pump enormous quantities of nitrates into the natural atmospheric and biological cycling of nitrogen. Overuse of nitrogen fertilizers are a primary cause of "dead zones" in coastal waters because nitrates are highly soluble; any nitrates not taken up by plant roots move quickly down through the root zone and enter ground water. When nitrate-laden rivers enter bays and estuaries, the excess nitrogen can cause larger than normal algae blooms. Decomposing algae draws oxygen from the water. Too large a drawdown of oxygen renders the water incapable of supporting most aquatic fish and animal life; anything that cannot swim or crawl out of the dead zone suffocates. The Mississippi River fertilizes a dead zone in the Gulf of Mexico that fluctuates in size from 3,000 to 8,000 square miles.
Nitrates may create a dead zone of sorts on the land as well. Epidemiological studies have linked nitrates in drinking water to reproductive problems and bladder and ovarian cancer. When nitrate-contaminated well water is mixed with infant formula and fed to babies, the infants can suffer from methemoglobinemia, or blue baby syndrome. The nitrates decrease the oxygen-carrying capacity of infant's blood, causing them to develop a peculiar blue-gray skin color and to become lethargic and irritable. If the condition is not treated rapidly, it can quickly progress to coma or death.
If you're feeling a need to take a deep breath, don't. Oxidized forms of nitrogen -- often released when fertilizer is applied -- contribute to the formation of smog. Smog increases the incidence of asthma and chronic respiratory diseases, and can worsen viral infections. When nitrogen oxides rise to the midlevel atmosphere, they serve as a greenhouse gas, contributing to global warming. In the upper atmosphere, oxidized nitrogen destroys ozone. Holes rent in the stratospheric ozone permit more ultraviolet light to reach the Earth's surface, increasing the incidence of skin cancers.
Finally, nitrogen oxides also contribute to acid rain, reacting with water in the atmosphere to form acidic compounds. When the compounds rain on or wash into lakes and rivers, they jeopardize fish, plant and bacteria populations that are sensitive to changes in water pH. As it percolates through the soil, acid rain leaches nutrients such as calcium, magnesium and potassium out of the root zone and mobilizes aluminum, which inhibits root growth.
Far more than an arbitrary distinction between natural and synthetic, the National Organic Program's ban on industrially fixed nitrogen is key to creating agricultural systems that don't depend upon increasingly scarce fossil fuels and that don't degrade the environment. Nitrogen is natural: an integral part of the systems of life on Earth. As such, artificially ramping up its availability jeopardizes the integrity of these very systems.
Permission granted to DIrt Doctor, Inc. from the author Deborah K. Rich to use the article. Feb 2006
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