B.13C_Nitrogen_onlevel – 03

The plants that have nodules on their roots are called legumes. Bacteria live in the root nodules. Legumes are nitrogen rich because the bacteria in their nodules add useful nitrogen to the soil. The organic farmers will rotate their corn crop with a legume. Alfalfa, beans, peas, and clovers are all legumes. Alfalfa is a legume with very deep roots and many nodules. These factors cause alfalfa to be extremely nitrogen rich. The farmers will use alfalfa to replenish the nitrogen in the soil lost to the corn. They will alternate between corn crops and alfalfa crops from one harvest season to the next. The corn will remove nitrogen from the soil, but the alfalfa will add nitrogen to the soil. This rotation of crops helps to maintain adequate nitrogen levels in the soil.

After harvesting crops, organic farmers plow leftover plant scraps into the soil. The remains are allowed to naturally break down and decompose. There are special bacteria in the soil called decomposers. The nitrogen compounds in the dead matter and wastes are changed to usable forms of nitrogen by decomposers. This provides another natural source of nitrogen for the next crop.

Nitrogen is returned to the atmosphere to complete the nitrogen cycle. There are specialized bacteria that convert nitrate ions back into nitrogen gas. On land, these bacteria are found mainly in soggy soil. In aquatic ecosystems, they are found in sediments at the bottom of oceans, lakes, and swamps. The nitrogen gas formed by the bacteria is released back to the atmosphere. The molecules of nitrogen gas in the atmosphere are available to begin the nitrogen cycle again. Organic farmers understand that disrupting the nitrogen cycle can interrupt the flow of nitrogen through the ecosystem. Organic farming strives to have very little impact on the surrounding ecosystems.

Organic farmers understand that overuse of inorganic fertilizers over time causes an excess of nitrogen in the soil. Excess nitrogen in soil is carried by runoff water into local rivers, streams, lakes, and ponds. The excess nitrogen causes an overgrowth of algae that is referred to as an algal bloom. An algal bloom depletes the oxygen levels in the water. The low oxygen levels can create a dead zone where aquatic organisms cannot survive.

Many other human activities disrupt the nitrogen cycle. The destruction of forests, grasslands, and wetlands removes large amounts of stored nitrogen. The nitrogen is no longer available for the abiotic factors in an ecosystem. Natural events also disrupt the nitrogen cycle. Volcanic eruptions and forest fires suddenly release large amounts of stored nitrogen into the air. Landslides and earthquakes bury and store large amounts of nitrogen. The nitrogen may not be available to cycle for long periods of time.

Nitrogen is a building block of all living things. Atoms of nitrogen move between living and non-living components of ecosystems. Nitrogen moves from the atmosphere to soil and water. Nitrogen moves through bacteria, producers, and consumers. It returns to soil and water, then back to the atmosphere. This nitrogen cycle allows atoms of nitrogen to be recycled repeatedly throughout different parts of the earth.