This simply refers to the complex process by which nitrogen is added or removed from the soil. The earth's atmosphere contains about 78% of nitrogen. Plants utilize nitrogen when it is converted to nitrate for making chlorophyll and protein.

  Nitrate is the form in which atmospheric nitrogen is absorbed by plants.

            Ways through which atmospheric nitrogen can be converted to nitrate;

     *Nitrogen fixing bacteria(symbiotic bacteria).

     *Nitrogen fixation.

     *Blue-green gae(anabaena and nostoc)

     *Thunderstorm.

     *Decay.

     This is the transfer of matured pollen grains from the anther to the stigma of a flower of the same kind.

     Agents of pollination; 

  *Animal(insects, birds, man, bat).

  *Wind.

  *Water.

  *The growth of stigma towards the anther to make contact.

       Types of pollination 

  *Self pollination--This is the transfer of pollen grains from the anther of a flower to the stigma of another flower on the same plant.

   *Cross pollination--This is the transfer of pollen grains from the anther to the stigma of another plant but of the same species.