Fertilisers are given to plants to promote growth. They can be naturally occurring compounds (such as peat) or they can be manufactured - either through natural processes (such as composting) or chemical processes. Fertilisers commonly contain nitrogen, and the use of such fertilisers emits the potent greenhouse gas, nitrous oxide (N20). Using animal manure as fertiliser, though organic, releases another potent greenhouse gas, methane into the atmosphere.