Ammonification is the process where fungi and bacteria break down dead organisms and waste products, releasing the nitrogen trapped in organic matter back into the soil as ammonia. It is one of five major transformations in the nitrogen cycle, alongside nitrogen fixation, nitrification, denitrification, and anammox. Without ammonification, the nitrogen locked inside every dead leaf, animal carcass, and dropping of waste would stay bound in complex organic molecules, unavailable to living plants and soil microbes.
How Ammonification Works
Every living thing contains nitrogen in its tissues, primarily in the form of proteins, amino acids, and DNA. When an organism dies or produces waste, that nitrogen is still tied up in these large organic molecules. Decomposing microbes, collectively called ammonifiers, go to work on this material in stages.
First, bacteria and fungi release enzymes outside their cells that chop proteins into smaller peptides and individual amino acids. Bacteria tend to produce one family of protein-cutting enzymes, while fungi produce a different set, but the end result is the same: large molecules get broken into pieces small enough for microbes to absorb. Once inside the cell, a key reaction strips the nitrogen-containing group off amino acids, a chemical step called deamination. The enzyme that handles this converts the amino acid glutamate into ammonia and a leftover carbon skeleton. Another important reaction is the breakdown of urea (a common component of animal urine) by an enzyme called urease, which splits urea into ammonia and carbon dioxide. The ammonia released through these reactions dissolves in soil water and becomes ammonium, a form of nitrogen that plant roots can absorb directly.
Which Organisms Drive the Process
Ammonification is not the work of a single specialist species. A wide range of soil bacteria and fungi participate, which is why it happens reliably in virtually every ecosystem on Earth. Among the fungi, species within the genera Aspergillus, Alternaria, and Paecilomyces have been identified as active ammonifiers in soil studies. Many common saprophytic bacteria, the kind that thrive on decaying organic matter, also contribute. Research on forest soils found that the total abundance of bacteria in the soil was a significant predictor of how fast ammonification occurred, second only to the concentration of dissolved organic nitrogen available as raw material.
This diversity matters. Because so many different microbes can perform ammonification, the process is remarkably resilient. Even if conditions shift enough to suppress one group of organisms, others typically fill the gap and keep nitrogen cycling.
Where Ammonification Fits in the Nitrogen Cycle
The nitrogen cycle has several steps, and ammonification connects the “death and decay” side of the cycle to the “growth and uptake” side. Here’s how it relates to the other major processes:
- Nitrogen fixation converts atmospheric nitrogen gas into ammonia, adding new nitrogen to the soil. Ammonification doesn’t add new nitrogen. It recycles nitrogen that was already in living tissue.
- Nitrification picks up where ammonification leaves off. Specialized bacteria convert the ammonium produced by ammonification into nitrite and then nitrate, another form of nitrogen that plants absorb readily.
- Denitrification closes the loop by converting nitrate back into nitrogen gas, returning it to the atmosphere.
In practical terms, ammonification is the recycling step. It takes nitrogen out of dead organic matter and puts it back into a simple mineral form that either plants can use directly or nitrifying bacteria can convert further.
What Controls the Rate of Ammonification
Several environmental factors speed up or slow down ammonification in soil.
Temperature has a strong effect. In controlled experiments testing soils across a range of conditions, mineralization (the broader process that includes ammonification) was greatest at 40°C. That’s notably warmer than the optimum for nitrification, which peaked at 20 to 30°C and essentially stopped at 40°C. This means that in hot conditions, ammonium can accumulate in soil because it’s being produced faster than nitrifying bacteria can process it.
Soil pH also plays a role, though ammonification is less sensitive to acidity than nitrification is. Ammonifying organisms function across a wide pH range, from strongly acidic soils (pH 3.6) to near-neutral soils (pH 7.5). The availability of dissolved organic nitrogen in the soil is the single strongest driver of gross ammonification rates, which makes intuitive sense: more raw material means more ammonia output.
Moisture matters too. Decomposing microbes need water to function, so waterlogged or bone-dry soils both slow the process, though for different reasons. Waterlogged soils limit oxygen, while very dry soils limit microbial activity overall.
Why It Matters for Plant Growth
Ammonium produced by ammonifying microbes, along with nitrate produced by nitrifying microbes, are the two main forms of nitrogen that plants can actually take up from soil. In forest ecosystems, research has shown that the type of nitrogen available to plants can vary dramatically over short distances. A study on forested hillslopes found that ammonium dominated in upper slope positions where ammonification was high but nitrification was low, while nitrate dominated in lower slope positions where nitrifying bacteria were more active. The gross rate of ammonium production stayed fairly constant across the entire slope, but what happened to that ammonium afterward determined which nitrogen form plants had access to.
For farmers and gardeners, this has a practical implication. Soil conditions that favor ammonification but suppress nitrification (acidic or very warm soils, for instance) will tend to accumulate ammonium. Conditions that support both processes will cycle nitrogen through to nitrate more quickly. Since nitrate is more mobile in soil and more prone to leaching away with rainfall, managing this balance affects how much nitrogen actually stays in the root zone.
Ammonification in Composting
Composting is essentially managed ammonification and decomposition. The same microbial processes that recycle nitrogen in forests and grasslands happen in a compost pile, but the concentrated organic matter and high temperatures can cause a significant amount of ammonia to escape into the air as gas rather than staying in the finished compost. This ammonia loss, called volatilization, wastes nitrogen that could otherwise enrich the final product.
Researchers have tested various additives to reduce this loss during aerobic composting of nitrogen-rich materials like chicken manure. Combining biochar (a charcoal-like material) with mineral conditioners reduced ammonia volatilization by up to 59% compared to untreated compost piles. Even simpler mineral additives alone cut ammonia loss by 27 to 35%. These approaches work by either absorbing ammonia before it escapes or by shifting microbial activity to retain more nitrogen in stable forms.
Urease Inhibitors in Agriculture
In farming, one common scenario involves urea fertilizers. When urea is applied to fields, soil microbes rapidly break it down through ammonification, releasing ammonia. If conditions are warm or the soil is alkaline, much of that ammonia can volatilize into the atmosphere before crops benefit from it. Urease inhibitors are chemicals added to urea fertilizer that temporarily slow this breakdown, giving the urea time to dissolve deeper into the soil where the released ammonia is more likely to stay put.
Field trials have shown that urease inhibitors significantly reduce ammonia volatilization from urea, though their effectiveness depends on soil type. Clay-rich soils respond better to the inhibitor, while acidic soils reduce its effectiveness. This is one of the few cases where deliberately slowing ammonification is the goal, since the process itself is essential but its timing and location need to be managed for efficient crop nutrition.