Nutrient Cycles And Nitrogen Cycle: Meaning, Stages And Examples

Biology

Topic: Nutrient Cycles And Nitrogen Cycle

Table of Contents

  • Meaning Of Nutrient Cycles
  • Meaning Of Nitrogen Cycle
  • Stages Of Nitrogen Cycle

Meaning Of Nutrient Cycles

Nutrient cycles refer to the circulation of certain nutrients like nitrogen, carbon, sulphur and water in nature.

Meaning Of Nitrogen Cycle

Nitrogen cycle involves the complex process by which nitrogen is naturally added and removed from the soil. It is a sequence of reaction indicating the various means by which nitrogen is added to and removed from the atmosphere and the soil.

Nitrogen fixation process involves soil organisms which add reasonable amount of nitrogen to the soil.

Nitrogen cycle involves the following stages:

1. Symbiotic nitrogen fixation: Some bacteria such as rhizobium leguminosarium which live in the root nodules of leguminous plants can fix atmospheric nitrogen directly into the plant. The plant supplies carbohydrate for use by the bacteria while the bacteria supply the plant with combined nitrogen.

2. Electrical discharge: Nitrogen can also be fixed into the soil during lightning and thunderstorm. Nitrogen in the air combines with oxygen to form nitric oxide or nitrogen (ii) oxide which further undergoes oxidation to form nitrogen dioxide or nitrogen (iv) oxide.

3. Non-symbiotic nitrogen fixation: Some bacteria such as Azoyobacter and Clostridium also live freely in the soil and can fix atmospheric nitrogen into the soil either aerobically or anaerobically.

4. Ammonification and nitrification: The process involving the formation of ammonium compounds from the dead and decaying of plants and animals and their waste products like urine and faeces is called ammonification. A further reaction known as nitrification involves the conversion of ammonium compounds first into nitrite by nitrifying bacteria called nitrosomonas. These nitrites are converted by oxidation to nitrates by another bacteria called nitrobacter. Plants can only absorb nitrates from the soil.

5. Dentrification: This is the process which involves the conversion of nitrate to nitrogen gas by certain bacteria. The nitrogen gas so formed can escape into the air.

Note: Denitrification is the only major stage in which nitrogen can be lost from the soil while other stages involve the fixing of nitrogen into the soil.