According to the 2008 Report on the Environment provided by the Environmental Protection Agency, the United States used an average of 136 pounds of inorganic fertilizer per acre. This doesn't begin to account for home synthetic fertilizer use. While the use of fertilizers has helped increase food production, it has also led to surface water pollution, groundwater pollution, soil degradation and health hazards.
Crop rotation using legumes and fertilizing with animal and human manure has been practiced for hundreds of years. In the 1840s, European scientists determined the three vital elements for plant growth were nitrogen, phosphorus and potassium. Chemical processes to produce phosphorus and potassium began in earnest. In 1913, two German scientists looking for an alternative to Chilean saltpeter for fertilizer and explosives developed the Haber-Bosch process. Through a heat-and-pressure-intensive process, they produced ammonia, a soluble form of nitrogen.
The idea that more chemical fertilizer will always produce better results is false. Excess fertilizer, especially nitrogen, leeches into groundwater and runs off into streams, lakes and ponds. All the excess energy and expense to produce the fertilizer, plus the expense and time used by the consumer, is wasted.
The pollution from over-fertilizing with chemical fertilizers causes algae blooms in surface water that can kill aquatic life. Excess nitrogen that enters the water supply for people can cause blue baby syndrome (methemoglobinemia) in infants when the concentration is more than 10 parts per million of nitrate nitrogen. Add to these hazards the fact that the production of chemical fertilizers uses a lot of biofuels, producing its own cadre of greenhouse gases and air and water pollution. The excess fertilizer has now become nothing more than pollution and a waste of resources.
Organic fertilizers come in the form of animal manure, compost, aquatic emulsions--such as fish emulsion--and "green" manure. Green manure is atmospheric nitrogen fixed by bacteria that has a symbiotic relationship with legumes, such as peas, lentils, clover and soybeans. Once the nitrogen is fixed, or converted from atmospheric nitrogen into ammonia, it becomes food for the legumes and future crops. Far superior to purchasing organic fertilizers--which must be harvested, packaged and shipped--is the practice of recycling organic materials locally, instead of trashing them or allowing them to run off into water supplies.
Even more important than choosing organic or inorganic fertilizers is determining whether you need fertilizer at all, how much you need and what kind suits your needs. Excessive use of manures can pollute water supplies just as readily as inorganic fertilizers. Return organic wastes to the garden or field via mulch or compost for the primary source of nutrition, then test the soil before adding any fertilizers. To do otherwise is to potentially waste time, money, energy and valuable resources.