Nitrogen Cycle Assignment
Draw a diagram including all the information written below relating to the
nitrogen cycle. Use arrows to show the direction the nitrogen is moving.
Nitrogen Cycle
Nitrogen makes up most (78%) of our air. Plants and animals need nitrogen,
but they are not able to use the nitrogen directly from the air. The nitrogen
must first be “fixed” before plants can use it. Some kinds of bacteria that live
in the soil are able to take nitrogen from the air and “fix” it into something
called nitrates. Nitrates in the soil are taken up by plant roots and used by
the plants to grow. Animals eat the plants and are eaten by other animals.
The nitrogen in the plants and in the bodies of animals returns to the
atmosphere when they die and decay.
Humans are changing the natural nitrogen cycles on the earth by using
nitrate-containing fertilizers on farmland. The extra fertilizer can wash into
lakes and rivers where it causes an overgrowth of algae. When the algae die
and decay, the oxygen level in the water drops. Low oxygen levels in the
water can kill fish and other animals that live in the water.
Humans also change the nitrogen cycle by planting the same crop, such as
corn, year after year on the same land. Eventually the soil becomes
depleted of nitrogen. To prevent soil depletion, farmers will plant crops
such as beans or clover which put nitrogen back into the soil. This practice
of alternating crops is called crop rotation.