Fertilizers are the largest single source of emissions from agriculture
"According to the Stern Review, a major report on the economics of climate change commissioned by the British government, fertilisers are the largest single source of emissions from agriculture (followed by livestock and wetland rice cultivation), as they bring huge amounts of nitrogen into the soil, which is later emitted into the atmosphere as nitrous oxide. The same report calculates that total agriculture emissions are expected to rise by almost 30 per cent in the period to 2020, with around half of the expected increase coming from the increased use of fertilisers on agricultural soils."
Seedlings Magazine, July 2007