Written evidence submission from the Agricultural Industries Confederation (NIT0015)
Agricultural Industries Confederation
House of Lords Inquiry into Nitrogen
Nitrogen Use in UK Agriculture
Executive Summary
Mineral Nitrogen Fertilisers
The very large increase in the UK and global populations of mankind and his animals over the past 150 years has meant that the naturally available nitrogen, from legumes and recycling, is capable now of providing only about half the global requirement for human, animal and plant proteins and food. The balance is now essentially provided by mineral fertilisers.
• These are formulated and applied in a timely manner and at a rate to precisely match anticipated crop demand and to minimise nutrient loss.
• They involve an application quantity which is only about 2% of that of manures and digestates.
• Their usage has halved over the past 40 years and is now less than the quantity used 50 years ago due to improvements in agricultural efficiency.
• Nitrogen Use Efficiency (NUE) for mineral nitrogen fertiliser is at its highest recently recorded level.
Manures and Digestates
The efficient recycling of the nutrients contained in these materials presents an unavoidable challenge for farmers, having significant potential for losses of reactive nitrogen to air and water.
• They are typically 6–10% total dry matter with a correspondingly high water content, requiring application volumes about 50 times greater than equivalent mineral fertilisers. This high volume significantly increases the potential for loss, particularly from run-off.
• They have inconsistent and low nutrient contents which makes accurate application difficult and complicates good Nutrient Management Planning.
• Insufficient on-farm storage capacity can result in excessive and untimely application to land, maybe as a means of ‘waste disposal’ rather than when the crop needs the nutrients.
• Over 90% of livestock manures are produced in predominantly grassland areas, with logistics reducing the potential for the use of these manures on arable farms.
Key Challenges For The Farm Circular Economy- What Needs To Change
• Increasing on-farm storage capacity with adequate environmental protections.
• Reducing the water content and improving the portability of manures and digestates.
• Addressing nutrient inconsistency to enable more precise application.
• Managing contaminants originating from waste material sources.
Key Opportunity For Reducing Impact Of Nitrogen Use On Farm
• Increasing Nitrogen Use Efficiency (NUE) on farm – (particularly from livestock husbandry).
• NUE needs to be measured and improved on a field by field basis towards 80-90%
About the AIC
As the UK agricultural supply industry's leading trade association, the Agricultural Industries Confederation (AIC) represents businesses in key sectors within the supply chains that feed the nation.
Our Member businesses supply UK farmers and growers with the animal feed, fertiliser, seed, crop protection products, trusted advice and quality services that are essential to producing food, as well as trading crops and commodities (Combinable Crops) across the globe.
Formed in October 2003 by a merger of three trade associations, today AIC has over 230 Members in the agri-supply trade and represents £17.8 billion turnover at farmgate.
AIC works on behalf of its Members by lobbying policymakers and stakeholders, delivering information, providing trade assurance schemes, and offering technical support.
www.agindustries.org.uk
Key Evidence
Natural and Mineral Nitrogen Fertilisers Use in UK Agriculture
The UK’s agricultural sector relies on manufactured nitrogen fertilisers in addition to nitrogen-fixing crops such as legumes to sustain food production at levels necessary to support the population.
While organic materials such as manure, compost and digestate contribute to soil fertility, they primarily function as nitrogen recyclers rather than sources because they redistribute existing nitrogen within the system rather than introducing new inputs.
Manufactured fertilisers are necessary to replace nitrogen lost through natural processes such as leaching, volatilisation, and denitrification, ensuring continuous agricultural productivity. The pathways of loss of N are natural and not of our making. This N-cycle in the natural state is in equilibrium, with all inputs and outputs being in balance.
The global cycle is very large and was sufficiently well buffered to be able to accommodate an increase in the size of the “Animals” box due to human population growth for many millennia without too much disturbance of the balance and thus changes in the scale of the pathways.
However, eventually the population grew sufficiently large that the natural availability of reactive nitrogen started to become insufficient to provide the quantity and protein content of the food necessary to feed the world, despite temporary support provided by guano and Chilean nitrate.
If the technological breakthroughs which led to the synthesis of additional reactive nitrogen, notably the Haber-Bosch process, had not occurred there can be no doubt that the human population would have become limited by the lack of sufficient food. This effect could have been delayed by the expansion of the food-producing area, mining the nutrients in the fresh soil, but this respite would have been temporary.
Thus the global population continued to grow during the 20th century, taking advantage of the additional availability of reactive nitrogen. Unfortunately, of course, the increase in inputs of reactive N led to an increase in all the natural pathways within the nitrogen cycle, including those resulting in losses; this has now rightly become a matter of concern.
Because the N-cycle is fundamentally a natural system of organic processes it is difficult to manage; this is particularly the case where the reactive nitrogen is incorporated within organic matter, such as in manures, biosolids, digestates, etc. The fact that the nitrogen in manufactured fertilisers is in the precise chemical forms which are required and taken up by plants, i.e. as ammonium and nitrate, enables it to be managed relatively precisely in respect of the needs of the growing crop.
Nevertheless, it is still part of the overall N-cycle and some inevitably travels down the natural pathways of loss, usually having passed through several biological processes: in the soil itself, the soil microbial biomass, the crop and in the animals, including humans, which consume the crop.
Manure Usage
In the United Kingdom, approximately 170 million tonnes of animal manure are produced annually, primarily from cattle on beef and dairy farms, compared with 2.6 million tonnes of nitrogen fertilisers. In 2024, 78% of agricultural holdings applied manure or slurry to their grass and arable lands. Of these, 36% managed the spreading exclusively by the farmer, 24% relied solely on contractors, and 19% utilized both farmers and contractors. Regarding storage practices, 66% of farms stored solid manure uncovered on field sites, while 34% kept it uncovered on concrete bases. Covered storage methods were less common, with 25% of farms using covered facilities. These figures underscore the importance of effective manure management in UK agriculture to mitigate environmental impacts.
"Estimates of Manure Volumes by Livestock Type and Land Use for England and Wales," data.gov.uk, https://www.data.gov.uk/dataset/6f966e56-2fac-42a9-9be9-c1529d4e5229/estimates-of-manure-volumes-by-livestock-type-and-land-use-for-england-and-wales
"Fertiliser, Manure and Slurry Spreaders," Farm Practices Survey February 2024, GOV.UK, https://www.gov.uk/government/statistics/farm-practices-survey-february-2024/fertiliser-manure-and-slurry-spreaders
"Manure and Slurry Storage," Farm Practices Survey February 2024, GOV.UK, https://www.gov.uk/government/statistics/farm-practices-survey-february-2024/manure-and-slurry-storage
"Soil Nutrient Balances UK, 2023 - Statistics Notice," GOV.UK, https://www.gov.uk/government/statistics/uk-and-england-soil-nutrient-balances-2023/soil-nutrient-balances-uk-2023-statistics-notice
Anaerobic Digestate in the UK
As of 2025, the UK's anaerobic digestion (AD) industry processes over 25 million tonnes of organic waste annually, producing significant amounts of digestate used primarily as fertiliser (NNFCC).
Whilst specific figures for total digestate production are not readily available, it is estimated that for every tonne of organic waste processed, approximately 0.8 to 1 tonne of digestate is produced. This suggests that the UK generates roughly 20 to 25 million tonnes of digestate each year (Anaerobic Digestion & Bioresources Association (ADBA)).
The composition of digestate varies depending on the feedstock used in the AD process. In 2019/20, about 34% of feedstocks in operational UK AD plants were crop-derived, with the remaining 66% comprising non-crop wastes such as food waste and manure (UK Government Statistics).
By April 2022, the number of operational AD facilities had increased to 660, with a robust development pipeline indicating continued expansion (NNFCC).
In 2022 AD production and use was responsible for 10.5% of the total agricultural emissions of ammonia, up from virtually nil 15 years previously.
Sewage Sludge Usage
• Quantity of sewage sludge spread on farmland: ~2,500,000 wet tonnes
• Quantity of sewage sludge spread on forestry land: ~50,000 wet tonnes
Sludges and digestates from biosolid waste due to the unseparated waste streams come loaded with Persistent Chemicals, microplastics, heavy metals, human sex hormones and pathogens.
(Thames Water 2025 – Nutrient Recovery Working group)
Mineral Nitrogen Fertiliser Use
~ 2.6 million million product tonnes of mineral ntrogen per year are supplied to UK agriculture (871kt mineral Nitrogen) (AIC)
Nitrogen fertiliser use from mineral sources has declined significantly since the mid 1980’s and is now 50% lower than it was 40 years ago. This trend appears to be continuing.
BSFP and AIC Statistics
Where are the Nitrogen losses coming from?
Poor practice – involving liquid phase manures, slurry, anaerobic digestate and wastes (Photo Source: Environment Agency)
Slurry application to waterlogged soil, no soil and crop need for nutrients
Farmyard manure applied to frozen ground, no soil and crop need for nutrients
Liquid waste applied to waterlogged soil, no soil and crop need for nutrients
High trajectory slurry application to waterlogged soil, no soil and crop need for nutrients.
Farmyard manure and runoff within 10 metres of a watercourse
Leaking weeping wall slurry store.
Liquid food waste applied to waterlogged soil
Slurry application to waterlogged soil
Digestate application to waterlogged soil
Health Constraints
Circular economy products are by their definition derived from waste streams, as such they can only be as safe as the materials from which they are derived, Animal manures will contain whatever pathogens or aliments the animal suffered from, which are passed directly onto the land, or will contain medical treatments that the livestock were treated with.
Limitations of Natural Nitrogen Sources
Limitations of Organic Nitrogen Recycling and Fixation
• Manure and slurry redistribute existing nitrogen but are regionally inconsistent and inadequate for current productive farming. They typically have a low nitrogen content and usually a high water content. This leads to significant storage challenges on farm and consequential disposal issues, where not infrequently slurry is spread on land as a means of disposal, rather than as a deliberate and accurate nutrient supplementation on land where it could make the best contribution to crop and grass production.
• Leguminous crops fix atmospheric nitrogen but can make only a relatively small contribution the nitrogen demands of current agricultural systems.
• Compost and green manure contribute valuable carbon to the soil ecosystem, like other manures, but release their modest nitrogen contents unpredictably, being often misaligned with crop growth cycles.
Attempting to rely solely on nitrogen from organic materials would require a major increase in livestock numbers to produce sufficient manure, with an associated large increase in the loss of nitrogen as ammonia, and also greatly expanded legume cultivation for biological nitrogen fixation. Both approaches would demand significant additional farmland, which is constrained in the UK, making this strategy impractical.
Sources Of Nitrogen In The Environment From Farming
Sources of Gaseous Nitrogen Compound Emissions to the Air.
Mineral nitrogen fertiliser use has substantially declined over 50 years, emissions have also declined in lock step.
Mineral nitrogen fertiliser use has declined by 50% over the past 40 years, gaseous emissions of fertiliser-related reactive nitrogen have also declined by 43% between 1990 (the first year for which data are available) and 2022. Over the same period the fertiliser-related emissions as a proportion of the total agricultural emissions has declined by 22%.
However, while livestock-related emissions have declined by about 20% since 1990, and are directly related to animal numbers, their contribution of two-thirds (66.6%) of all agricultural gaseous emissions of nitrogen remains unchanged over the period.
Note different scales on the y-axis of the two gaseous emissions charts.
Improved agronomic advice (FACTS Advisors) and precision application of mineral fertilisers has led to an improvement in Nitrogen Use Efficiency (NUE) and farm copping outputs generally.
"The application of cattle slurries to the silty clay loam soil increased the loss of solids and ammonium-N in surface water flow compared to control plots receiving inorganic fertiliser only, or no treatment, but had little effect on nitrate-N losses by this route." "Increasing slurry application rate and, in particular, slurry solids loading, increased solids and ammonium-N losses via surface run-off."
K Smith et al., (2001). Nutrient Losses by surface run-off following the application of organic manures to arable land. Environmental Pollution, 112(1), 41-51.
"Leaching losses from arable crops are relatively small and are mainly controlled by the weather provided no more than the economic optimum amount of N fertilizer is applied.
Farmyard manure can produce good crop yields but is prone to large leaching losses when applied in autumn, and especially when applied regularly over an extended period to build up soil organic matter."
Goulding K W T et al. (2000). Nitrate leaching from the Broadbalk Wheat Experiment, Rothamsted, UK, as influenced by fertilizer and manure inputs and the weather. Soil Use and Management 16, 244-250.
Conclusion
If we are to successfully manage nitrogen (and indeed phosphorus) from agriculture, we need to eliminate the water volume from slurries and digestates to render them more concentrated.
This will allow for their transportation and accurate application to land that requires any nutrients they may contain, rather than managing the material as a waste product, as is currently the case.
Liquid manures and digestates are not a solution but rather the problem. Unless their format can be altered, they will remain the major source of environmental pollution from farming.
07/03/2025