Agriculture main source (90%) of ammonia emissions in UK

Current estimates (2006) are 315 x 10³ t/year, of which 288 x 10³ t/year from agriculture.

Most ammonia losses occur after spreading livestock waste, 30% of the national total

28% of national total is derived from livestock housing

Losses from grazing, 10% of national total, from storage 5% of national total

Remainder from nitrogen, fertilizer and crops

Approx. 50% of N deposited in atmosphere in the UK is as ammonia, the remainder is as oxides of nitrate from combustion, transport and industry

Trend is moving in the right direction although it has slowed in recent years. The emission target set for 2010 under the UNECE Gothenburg Protocol and EU target  is 297 x 10³ t/year

Soil acidification

Nutrient enrichment (eutrophication) of non agricultural soils and water

Ammonia is very soluble in water so readily deposited in rainfall (see above diagram)

Loss of valuable farm nutrient resource

Urine of mammals contains urea, poultry excreta contains uric acid, both can both may be broken down to release ammonia to the atmosphere

Urea is hydrolyzed by the enzyme urease to ammonium carbonate, this disassociates rapidly in water to produce OH ions:  NH₃+H₂O = NH₄⁺+OH

At this pH ammonia is predominantly in NH₃ (molecular) form, and will diffuse into the air as long as the air concentration is lower than in the aqueous solution (urine etc.) 

Uric acid is hydrolyzed first to urea, by bacterial enzymes, the produced urea then behaves as outlined above

If poultry excreta is kept dry (< 30% moisture), then bacterial activity is inhibited, hence uric acid hydrolysis is inhibited and ammonia production is halted

Reduce N excreted by animals by matching dietary inputs to nutritional requirements (amino acid inputs in pigs and poultry are particularly high)

Most animal housing is naturally ventilated and it is not possible to remove ammonia from air as it leaves the building. Costs of fitting ammonia filter systems exceed the profit margins per animal place

50% of all animal excreta stored as solids (FYM)

No real successful method of reducing ammonia emissions

Slurry in above ground or underground tanks with cover reduce emissions by around 80% but risk of explosion etc.

Only 20% of cattle slurry and 40% of pig slurry in UK stored in tanks

Remainder stored in weeping wall or lagoons (open topped)

Injection of ammonia directly into soil, minimizing contact with air, therefore reducing diffusion

50% of animal waste produced in UK  cannot be injected, (solid FYM)

Rapidly incorporating manure or slurry by ploughing directly after spreading:

20 - 40% of UK soils are too shallow or stony for injection

Injection will increase nutrient loss by other methods, i.e. leaching

There is little scope for reducing ammonia diffusion from grazing

Ammonia losses from fertilizer spreading are significant (13% of total agricultural emissions) there are few methods of reducing them owing to:

Majority of N fertilizer used in the UK is ammonium nitrate and only 1-2% of the N is lost as ammonia

Ammonia loss from urea (10% of fertilizer N use) is much greater at c15% of N applied

Reducing ammonia losses, therefore requires replacement of urea with (more expensive) ammonium nitrate

Carbon dioxide

Methane

Nitrous oxide

Chlorofluorocarbons (CFC's)

Nitrous oxide is 310 times, and methane is 21 times, more potent than carbon dioxide in terms of radiative forcing over a 100 year period

CFC's rarely used in agriculture, except in refrigeration, but widely used in food industry

UK agriculture produces 38% of total methane, 66% of nitrous oxide and 1% of carbon dioxide in UK

Atmospheric methane is increasing at the rate of 30 - 40 Tg/year

Global emission of methane is estimated to be 540 Tg/year

Of this, 70 - 100 Tg/year from enteric fermentation from livestock and 35 Tg/year from animal wastes

Biogenic sources, eg. peat bogs & tundra - 25%

Rice paddies - 20%

Very little can be done at present

Reduce number of cattle, therefore enteric fermentation

Improve cattle production efficiency

Above two factors already underway by default. i.e. milk quota's, BSE, loss of farm incomes etc. (weeks 1 & 2) 

Some research work into methane reducing feed additives, but at present require withdrawal times so cannot be used on dairy cattle

Nitrous oxide (N₂O) - contributes to global warming. It is emitted from the soil and emission increases with N inputs.  The majority of nitrous oxide emissions in the UK is directly from soil - 63%.

Nitric oxide (NO) - contributes to acid deposition in soil, and formation of ozone in lower atmosphere. Emitted from soil in proportion to N inputs

Nitrogen Dioxide (NO₂) - very reactive, contributes to acid deposition, small amount emitted from soil, but most absorbed by crop canopy, soil generally ignored as a source of this gas

Others, e.g. (N₂O₅) - usually present in the air and for these purposes can be ignored

Reduce mineral N content of the soil by:

Analysis of soil from previous crop, manure applications, and soil organic matter before deciding on fertilizer policy

Timing of N applications to when crop has highest uptake potential

Timing of incorporation of organic manure and crop residues to avoid incorporating when soils are poorly aerated

Agriculture only produces 1% of UK's total CO₂ emissions

Road transport 22%

Residential homes 15%

Energy Industries 39%

Complaints of odour from agricultural sources compiled and summarized by Environmental Health Departments

Manure and slurry spreading - 44%

Livestock buildings - 25%

Manure and slurry stores - 21%

Pig farms highest number of complaints - 47%

Poultry units - 25%

Cattle - 22%

Depends on strength and source of odour and prevailing wind direction

There are no definitive or statutory criteria linking the frequency and concentration of odours to the occurrence of a nuisance. Guidelines have been set for other countries and industries:

Suburban areas - for no more than 2% of hours should average odour concentration exceed 5 OU/m³ 

Rural areas - for no more than 2% of hours should average odour concentration exceed 10  OU/m³

OU = Odour unit as measured by olfactomotry