Nitrogen is the most important nutrient for the growth of plants. It is the catalyst by which plants perform photosynthesis and utilize all other soil nutrients. In its natural form, it is present in the atmosphere as an inert gas and fixed in the soil by leguminous plants. Unfortunately, this is a slow and limited process. Manufactured nitrogen, captured from the air by a process invented in the early 20th century, can be added to the soil in far greater amounts than naturally produced nitrogen. This is responsible for the large increases in crop yields over the last 100 years. Long-term adverse effects to the planet's ecosystem due to the use of artificial nitrogen are becoming more apparent as more studies are conducted.
Underutilized by Plants
Manufactured nitrogen fertilizers contain many times more nitrogen than the plants actually need or use. In addition, cereal and grain varieties have been developed that utilize only 30 percent of available nitrogen in the soil. This is up from 80 percent utilization of nitrogen by cereal varieties grown in 1960, according to Yale University. All of the unused nitrogen artificially applied to the soil gets washed away in drainage water and enters the planet's water systems.
Accumulation in Water Systems
Nature has a way of removing excess nitrogen from waterways---called "denitrification"--which converts it back into the inert gas from which it came. Increasingly, the ecosystem is becoming overwhelmed with excess nitrogen and many rivers are losing their ability to perform denitrification. The nitrogen is carried through the watershed and finally deposited into the oceans.
Excess Algae Growth
Excess amounts of nitrogen in rivers eventually reaches the planet's oceans, causing an excess growth of algae. In some cases it is killing entire ecosystems and creating oceanic oxygen-depleted "dead zones," according to the Oak Ridge National Laboratory. The excess nitrogen over-fertilizes the water and produces a large volume of algae, which consumes all of the water's oxygen and causes the ecosystem to crash. This is most prevalent in coastal bays and inlets, as well as river estuaries.