What are the differences and similarities between the carbon cycle and nitrogen cycle and how can we identify them?

Similarities:  Both of these are biogeochemical cycles,meaning that the chemicals spend a portion of the cycle in living things (hence the bio) and a portion in the nonliving environment (geo). They are also similar in that they both recycle nutrients that are essential to all organisms.  Finally, they both move from the soil into plants via the roots, and then to animals through ingestion, and they can be returned to the environment via decomposition.

Differences:  They are different in the manner that they cycle.  Nitrogen gas is quite abundant (78% of the air around us is nitrogen).  It cannot be used by plants or animals in its gaseous form though. In order for it to be useful, it has to undergo nitrification (Nitrogen gas being changed into a usable form).  This is carried out by bacteria that live in nodules on the roots of some plants (like beans).  Once the nitrogen is used by the plant and makes its way to an animal, it can be released through decomposition or urination.  Once it is back in the soil, another type of bacteria cause denitrification, which turns it back into nitrogen gas. 

Carbon, on the other hand, requires no special processing by bacteria prior to plants and animals being able to use it.  Plants take in carbon dioxide and use it to make sugar.  Animals eat this sugar and incorporate it into their body.  Some of it is released as the carbon dioxide that we exhale.