Throughout the 20th century and into the 21st century, nitrous oxide in the environment has increased by 50 parts per billion. This atmospheric loading is increasing by 0.25% each year. Farmers in UK now get more reactive nitrogen from the air (particulates and acid rain) than they used to put on their land in 1950s. Once pesticide were "bad" and fertilsers "good". Now it may be the other way round.

N₂O is produced naturally in soils through the microbial processes of denitrification (during which water-soluble nitrates are converted to gaseous products, including nitrous oxide N₂O). These natural emissions are increased by a variety of agricultural practices

Direct addition of nitrogen to soils:
· use of synthetic and organic fertilisers
· production of nitrogen-fixing crops
· cultivation of high organic content soils
· application of livestock manure to croplands and pasture

80% of nitrous oxide emissions globally are associated with the agricultural and waste-treatment industries, most coming from artificial fertilsers (evidence?). Livestock accounts for about 65% of human made nitrous oxides according to LEAD.

Since the UK signed up to the Kyoto Protocol, many non-biological emissions have been reduced, but nitrous emissions from agriculture are essentially unchanged.

Source DEFRA Statistic for 06

Nitrates in water have been a concern for many years. New Nitrate Vulnerable Zones cover 70% of UK as part of implementation of Nitrates Directive