The UK Government announced in June 2019 its aim to bring all greenhouse gas emissions to net zero by 2050, and in response the NFU announced its net zero by 2040 pledge.
But what does this all mean in practice? In low concentrations, ammonia is not harmful to human health.
However, when ammonia emissions from agriculture combine with pollution from industry and transport, such as diesel fumes, they form very fine particulate matter.
This can be transported significant distances adding to levels to which people are exposed.
When inhaled, particulate matter can penetrate deeply into body organs and can be a contributory factor in cardiovascular and respiratory disease.
It is estimated that particulate matter emissions result in 29,000 premature deaths every year in the UK.
When deposited on land, ammonia can acidify soils and freshwaters, ‘over-fertilising’ natural plant communities.
The extra nitrogen can increase the growth of aggressive species, such as rank grasses and nettles, which then out-complete other species, such as sensitive lichens, mosses and herb species which have lower nitrogen requirements.
METHANE represents the largest proportion of greenhouse gases emitted from agriculture.
It is produced by livestock, as a result of ruminant enteric fermentation associated with the digestion of feedstuffs by bacteria in the stomachs of cows and sheep.
The principal source of CARBON DIOXIDE (CO2) on-farm is the burning of diesel and petrol for transport and electricity, when made from fossil fuels rather than renewable sources, which is used to power lights and used for cooling and heating.
Measures which disturb soil, such as ploughing or land use changes, also release CO2 from soil
NITROUS OXIDE (N20) is produced naturally in soils through microbial processes, but the application of mineral fertiliser or manures increases N20 emissions.
The amount of N2O emitted when applying fertiliser or manure to crops will vary depending on a variety of factors
AMMONIA (NH3) is not a greenhouse gas and only has a short lifetime in the atmosphere.
NH3 is formed when urease, an enzyme produced by micro-organisms in faeces, reacts with urea in the urine.
It is produced when fertilisers are applied to land, the most at-risk being urea.
NITROGEN is one of the four key plant nutrients required by crops in relatively large amounts to achieve their optimal growth, yield and quality potential.
Nitrogen can be applied in the organic form, as slurries and manures, or it can be fixed from the atmosphere by legumes, such as clovers and lucerne, or it can be applied as inorganic (mineral) fertilisers.
Mineral nitrogen fertilisers come in two main forms: n Urea fertiliser – when applied to land it goes through a chemical conversion process called hydrolysis to convert it into plant available forms of nitrogen n Ammonium nitrate fertiliser – contains two forms of nitrogen (ammonium and nitrate) in equal amounts.
Nitrate is immediately available for uptake while ammonium can be utilised by grass to an extent, but most is quickly converted to nitrate by soil micro-organisms.
A proportion of nitrogen applied to crops is lost, either to the air through volatilisation as ammonia, or by bacterial chemical conversion processes in the soil, known as nitrification and denitrification, producing nitrous oxide or through leaching.
The application of nitrogen fertilisers accounts for 18% of the UK’s agriculture-derived ammonia emissions; solid urea contributes 8% of the UK total.
There is significant scope to reduce this figure and the fertiliser industry and farmers both have an important part to play.
In 2014, 96% of the area of nitrogen-sensitive habitat in England received more nitrogen than it could cope with causing irreversible changes.
Philip Cosgrave, Yara country grassland agronomist, points to the Government consultation on the future of urea fertiliser, highlighting concerns about ammonia emission levels.
He says: “Urea is a mineral fertiliser produced in a chemical process by reacting ammonia with carbon dioxide.
A Defrafunded project from 2006 found that urea applied on grassland lost on average 30% of the applied nitrogen as ammonia versus 3% for AN.
The Government states it is seeking to substantially reduce ammonia emissions from fertiliser and has offered a number of options from an outright ban on its use, to restricting its use to spring applications only.
“To effect the same ammonia emissions, reductions from manure management would be costly in comparison to switching urea users to ammonium nitrate or urea with urease inhibitors.”
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