Why depreciation is not charged on land?

Your qurey is not clear as you are giving the answer answer along with the query

Land is not depreciated because land have an perpetual life i.e. unlimited useful life. 

Land is such an asset whose value will not go down. The reasons are many. One of which is the demand as the population goes on increasing the demand goes up and hence the prices. There may be temopary downwards trend due to the economic scenario. But in long term it will reap you profits. Hence depreciation is not provided on land.