Diffuse water pollution, GHGs and Ammonia emissions

Diffuse Water Pollution, Greenhouse Gas Emissions and Ammonia Emissions on your farm.

This information is a summary of information from a Defra project titled "An Inventory of Mitigation methods and guide to their effects on Diffuse Water Pollution, Greenhouse Gas emissions and Ammonia emissions from Agriculturewhich was conducted by ADAS and Rothamsted Research North Wyke. It aims to provide summarised information on a range of different management options on farm to reduce pollution (either diffuse water or air) and greenhouse gas emissions.

How to use the information on this page

1. Choose your farming sector and click on the link below to take you to the management options that are relevant to your farm.

2. The methods have then been subdivided into  categories:

  • Land use change
  • Soil Management
  • Crop and livestock breeding
  • Fertiliser management
  • Livestock management
  • Manure management
  • Infrastructure

3. Methods within these categories have been divided into time periods.

Short term - low cost or short term options that should be able to fit into most current management systems fairly easily without making major change or investment.

Medium term - options may require planning to implement or some investment and should be achievable in 1-2 years.

Long term - options that require either significant alteration to current farming systems or significant investment, and/or the introduction of innovative technologies that are just being developed.



Gas derived from urea excreted by livestock and from nitrogen fertilisers. It affects acidification and nitrogen enrichment of aquatic ecosystems (through eutrophication) and can be toxic to fish at high levels. The gas is released from solution by a process called volatilisation, which occurs from urine and manures during housing, storage and following land application.


Present in soils, fertilisers and manures. It is produced when micro organisms break down the urea and proteins in manure. This is not readily leached from soil but it can be lost in surface runoff and drainflow waters.

Biochemical Oxygen Demand (BOD)

A measure of the water pollution potential of organic materials. Surface waters with a high BOD, contain high concentrations of potentially damaging organic matter - which will deplete free oxygen levels and the ability of the water body to support many forms of animal life.

Carbon dioxide

Is the inorganic form of carbon cycled through photosynthesis and respiration. In agriculture, carbon dioxide is released from the burning of fossil fuels and when soils are disturbed following cultivation or land use change.

Faecal Indicator Organisms (FIOs)

These are micro organisms excreted by and present in, livestock excreta and manures. Their presence in water indicates contamination by faecal matter.

Click here to find out how to reduce the risk of FIOs contaminating water on your farm.


Has 25 times the global warming potential (GWP) of carbon dioxide. It is released from the digestive system of ruminant livestock by enteric fermentation and from solid manures and slurries.


Is an extremely soluble form of nitrogen. Because it is soluble, it readily moves with the soil water towards the plant roots to be taken up. However, if there is a large amount of water passing through the soil root zone it can be carried by the percolating water beyond the root zone. This usually occurs at the time of year when the soil is at field capacity and rainfall causes leaching to occur.

A high level of nitrates in drinking water can be harmful to humans, and more widely aquatic life.


Produced naturally as part of the process of converting ammonium into nitrate. It doesn't often accumulate in the soil and moves readily with soil water through the soil and into ground/surface waters. While nitrite is very toxic to aquatic life, it tends to convert quickly to nitrate.

Nitrous oxide

Has 298 times the global warming potential (GWP) of carbon dioxide.

Nitrous oxide is released during the production and use of manufactured fertilisers, as well as from animal manures. It is not possible to avoid nitrous oxide emissions from farming systems, but nitrous oxide production (by nitrification / denitrification) needs to be controlled and reduced.

Direct Nitrous oxide - from application of manufactured fertilisers and animal manures, and defecation whilst grazing.

Indirect Nitrous oxide - through nitrate leaching/run off and atmospheric deposition of N.


Phosphorus (P) is lost from agricultural systems via a number of pathways. It can be lost through soil erosion, where soil P has accumulated to elevated levels and/or where fertiliser and manure applications are followed by rainfall. Soluble and particulate P losses can occur via leaching/drainflow, surface runoff and erosion.

Phosphorus in watercourses can cause problems by increasing the risk of eutrophication which accelerates the growth of algae and other aquatic plants. Algal blooms may cause fish kills and may harm wildlife and livestock by reducing the oxygen content of the water or through producing toxins.


Increased sediment loadings can cause a range of environmental problems, including channel bed siltation and its associated detrimental impacts on fish populations, biodiversity or macro invertebrates and other species.

There is increasing evidence for the role of fine sediment in transferring nutrients to watercourses and contributing to diffuse pollution problems.