Ammonia clouds forming a question mark over a farm, symbolizing emission uncertainty.

Is Your Fertilizer Doing More Harm Than Good? The Hidden Truth About Ammonia Emissions

Soraya Malik in Climate & Environment August 2025 • 4 min read.

"Uncover how outdated European emission inventories may be overestimating ammonia release, impacting our environment and agricultural practices."

For years, European agricultural policies have been guided by a critical understanding: that ammonia (NH3) emissions from fertilizers significantly contribute to environmental harm. Emission inventories, such as those outlined in the EMEP/EEA guidebook, have set the standard, dictating that a large percentage of applied nitrogen fertilizer escapes into the atmosphere as ammonia. But what if these guiding principles are based on overestimated data?

A recent review has compiled over 350 measurements of ammonia emission factors (EFs) from 1991 to 2011, challenging the long-held assumptions about field-applied slurry. The findings suggest that the actual ammonia emissions may be substantially lower than what current inventories indicate, potentially reshaping how we approach agricultural sustainability and environmental protection.

This article will explore the intriguing discrepancies uncovered by this review, examining the methods used to measure ammonia emissions and discussing the implications for European emission inventories. It’s time to question the status quo and consider whether our efforts to minimize agricultural pollution are on the right track.

The Great Emission Overestimation?

Ammonia clouds forming a question mark over a farm, symbolizing emission uncertainty.

The EMEP/EEA guidebook, a key resource for agricultural emission inventories, reports that an average of 55% of the total ammoniacal nitrogen (TAN) content from cattle slurry and 35% from pig slurry is lost through volatilization. These figures are used across Europe to inform policies and practices, but they may not reflect the reality of modern agriculture.

The review of over 350 measurements reveals a significant shift in slurry application techniques over the years. In the early period, when many of the reference EFs were established, splash plate spreading was the standard method. However, more recent techniques, such as trailing hose, trailing shoes, and slurry injection, have become increasingly common. These newer methods are designed to reduce ammonia emissions, suggesting that the older, higher EFs may no longer be accurate.

To understand the significance of this potential overestimation, consider these factors:

Evolving Agricultural Practices: Modern techniques aim to minimize emissions, making older data less relevant.
Variations in Measurement Techniques: Different methods yield varying results, complicating the picture.
Impact on Environmental Policies: Overestimated emissions could lead to inefficient or misdirected environmental policies.

The review classified available measurements according to flux measurement technique, measurement plot size, and year of measurement. Medium-size plots, typically circles with a 20 to 50-meter radius, yielded the highest EFs, while field-scale measurements showed substantially lower EFs. This discrepancy calls for a reevaluation of measurement approaches and a validation of newer, more accurate inputs for emission inventories. The question is no longer just about the quantity of emissions, but about the methods we use to measure them.

Time for a Change?

The review underscores the urgent need for new measurement series to validate various measurement approaches and derive revised inputs for emission inventories. By refining our understanding of ammonia emissions, we can ensure that agricultural practices and environmental policies are based on accurate data. This, in turn, will lead to more effective strategies for reducing agricultural pollution and promoting a sustainable future.

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This article is based on research published under:

DOI-LINK: 10.5194/bg-9-1611-2012, Alternate LINK

Title: Are Ammonia Emissions From Field-Applied Slurry Substantially Over-Estimated In European Emission Inventories?

Subject: Earth-Surface Processes

Journal: Biogeosciences

Publisher: Copernicus GmbH

Authors: J. Sintermann, A. Neftel, C. Ammann, C. Häni, A. Hensen, B. Loubet, C. R. Flechard

Published: 2012-05-03

Everything You Need To Know

What is the EMEP/EEA guidebook, and how does it influence agricultural practices related to fertilizer use?

The EMEP/EEA guidebook is a key resource that provides emission inventories used to guide agricultural policies across Europe. It sets standards for the amount of ammonia emissions expected from fertilizers, specifically stating that a large percentage of nitrogen fertilizer applied is lost to the atmosphere as ammonia. The guidebook's data influences agricultural practices and environmental policies aimed at reducing pollution.

How does recent research challenge established assumptions about ammonia emissions from field-applied slurry?

The review of over 350 measurements suggests that ammonia emissions from field-applied slurry may be significantly lower than what current emission inventories, like those in the EMEP/EEA guidebook, indicate. This discrepancy is attributed to advancements in slurry application techniques, such as trailing hose, trailing shoes, and slurry injection, which are designed to reduce emissions compared to older methods like splash plate spreading.

What factors can influence the measurement of ammonia emissions, and why is it important to consider these variations?

The flux measurement technique, measurement plot size, and year of measurement can all influence the measurement of ammonia emissions. For example, medium-size plots (20-50 meter radius) tend to yield higher Emission Factors (EFs) compared to field-scale measurements. This inconsistency underscores the need to reevaluate measurement approaches to ensure accurate inputs for emission inventories.

According to the EMEP/EEA guidebook, what percentage of ammoniacal nitrogen is lost from cattle and pig slurry, and what are the potential implications if these figures are overestimations?

The EMEP/EEA guidebook reports that an average of 55% of the total ammoniacal nitrogen (TAN) content from cattle slurry and 35% from pig slurry is lost through volatilization. If these figures are overestimations, policies based on them could be inefficient or misdirected, leading to unnecessary restrictions or investments in mitigation strategies that may not yield the expected environmental benefits. Accurately quantifying ammonia emissions is crucial for developing effective and targeted environmental policies.

What steps are necessary to refine our understanding of ammonia emissions and improve the accuracy of emission inventories?

To refine our understanding of ammonia emissions and improve the accuracy of emission inventories, new measurement series are needed to validate various measurement approaches and derive revised inputs. These new measurements should account for modern agricultural practices and variations in measurement techniques. Updating emission inventories will ensure that agricultural practices and environmental policies are based on the most accurate data available, leading to more effective strategies for reducing agricultural pollution and promoting a sustainable future.