Nitrogen fertiliser spilling out of a torn bag. This fertiliser is added to the soil to encourage plant growth. It is mainly used for agricultural purposes to treat fields used for growing crops. Using nitrogen fertiliser is known as the Haber- Bosch process, the reaction of nitrogen and hydrogen to produce ammonia. Few plants engage in nitrogen fixation (conversion of atmospheric nitrogen into a biologically useful form). They therefore need nitrogen compounds to be present in the soil. This fertiliser is made using fossil fuels such as natural gas, which damages the environment. It is also considered to be a health hazard.