Is Chicken Manure Acidic or Alkaline?

Fresh chicken manure is typically alkaline, with a pH that generally falls somewhere between 7 and 9 depending on the birds’ diet, housing system, and how long the manure has been sitting. That puts it on the basic end of the scale, which surprises people who assume manure should be acidic because of all the organic acids produced during decomposition. The reality is more layered than a single pH reading suggests, because chicken manure’s chemistry shifts considerably as it ages, composts, or gets incorporated into soil.

Why Chicken Manure Leans Alkaline

Several chemical processes push fresh chicken manure toward a basic pH. The most straightforward is its high calcium carbonate content. Poultry rations, particularly those fed to laying hens, are loaded with calcium sources like limestone and oyster shell to support eggshell formation. A substantial portion of that calcium passes through the bird undigested and ends up in the manure, where it behaves much the same way agricultural lime does in a field. Research on organic amendments has identified the calcium carbonate content of poultry and pig manures as one of the major mechanisms responsible for elevating soil pH, along with the proton-consuming capacity of humic material and the breakdown of organic acid anions during decomposition.¹

The nitrogen content of chicken manure also matters. Poultry excrete nitrogen mainly as uric acid, which microbes rapidly convert to ammonia and then ammonium. That conversion is alkaline in nature. As nitrogenous components break down, they release ammonium-nitrogen, which pushes pH upward.² This is one reason fresh chicken manure smells so strongly of ammonia on a warm day: the ammonia gas volatilizing off the surface is a direct byproduct of the same reactions that make the manure basic.

How pH Shifts Over Time

Calling chicken manure “alkaline” is accurate as a snapshot, but the pH is not static. From the moment manure leaves the bird, its chemistry starts changing, and that trajectory depends heavily on what happens next.

In the first few days of decomposition, microbial activity generates volatile fatty acids, including acetic and butyric acid. These organic acids temporarily pull the pH downward. In anaerobic digestion experiments, volatile fatty acid production peaked within the first two to sixteen days depending on whether pH was controlled, with the highest production occurring at an initial pH of around 6.0.³ But in an open-air or aerobic setting, this acid phase is relatively short-lived. As decomposition continues, ammonia release and the buffering effect of calcium carbonate dominate, and pH climbs back up or stays elevated.

Composting introduces another dynamic. When chicken manure is mixed with a carbon-rich bulking agent like straw and turned regularly, physicochemical properties including pH change considerably over the composting period. A study tracking aerobic composting of chicken manure mixed with wheat straw over 35 days found that pH was one of the key indicators influencing microbial community succession throughout the process.⁴ In practical terms, a well-managed compost pile tends to finish with a pH somewhere in the neutral-to-mildly-alkaline range, often between 7 and 8, because the most volatile alkaline compounds have already been lost as ammonia gas during the thermophilic phase.

What Happens When You Add It to Soil

This is the question gardeners and farmers actually care about, and the answer is not as simple as “it makes soil more alkaline.” The immediate effect of applying chicken manure to soil is typically a bump in pH. A study that visualized soil pH changes in real time found that chicken manure increased pH within five days, raising the top two centimeters of soil by roughly 0.3 to 0.4 pH units compared to unfertilized controls.⁵ That initial rise makes sense given the calcium carbonate and ammonia content described earlier.

But here’s the catch: by 60 days after application, the pH in that same study had dropped back down again, following a trend similar to soils treated with nitrate-based synthetic fertilizers.⁵ The reason is nitrification. Soil bacteria convert the ammonium released from the manure into nitrate, a process that generates hydrogen ions and acidifies the surrounding soil. So while chicken manure behaves like a liming agent in the short term, over weeks and months its nitrogen content can actually contribute to soil acidification, the same way a synthetic ammonium fertilizer would.

Application rate matters too. A field trial evaluating poultry manure at rates of 5 to 20 tonnes per hectare on maize found that soil pH increased with application rate up to a point. At 10 tonnes per hectare, the pH increase was greatest. Above that rate, pH actually started trending downward again, possibly because of the larger nitrogen load accelerating nitrification and acid production.⁶ The relationship between how much you apply and how much the pH changes is not linear, and pouring on more is not always better if you are trying to raise pH.

The Liming Effect and Its Limits

Because of its calcium carbonate content, poultry manure is sometimes described as having a “calcium carbonate equivalence,” meaning it can partly substitute for agricultural lime. Tests on poultry layer manures from both coastal plain and piedmont soils confirmed that all manures exhibited effects on soil pH consistent with their calcium carbonate equivalence.⁷ For farmers working with acidic soils, this is genuinely useful: regular applications of chicken manure can reduce the amount of purchased lime needed.

The liming power varies enormously depending on the type of poultry operation. Layer manure tends to have higher calcium carbonate equivalence than broiler litter, because laying hens eat diets with far more calcium for egg production. Broiler litter, which is a mix of manure and bedding material like wood shavings or rice hulls, has its calcium diluted by those carbon-rich additives. A study comparing litter from different production systems found that litter from free-range broilers had the highest pH, while litter from intensive and free-range layer operations showed different electrical conductivity profiles.⁸ So “chicken manure” is not a single product; its pH and liming ability depend on what the birds ate, how they were raised, and what bedding was used.

If you are working with acid soils, chicken manure compost can be especially helpful for reducing the availability of toxic metals. In cadmium-contaminated soils, adding chicken manure compost raised pH enough to reduce soluble cadmium by more than 70 percent and cut cadmium uptake by wheat tissue by more than half.⁹ The pH increase tied up the metal in less available chemical forms. Similarly, long-term chicken manure application to acid paddy soils significantly reduced cadmium and lead in rice grain, though it also increased the availability of arsenic in the soil.¹⁰ The pH-raising capacity of chicken manure is real and useful, but it brings trade-offs that deserve attention.

Ammonia, pH, and the Smell Problem

If you have ever walked into a chicken house, you know the ammonia can be intense. That ammonia is directly tied to manure pH. When pH is high, the chemical equilibrium between ammonium (a dissolved ion that stays put) and ammonia (a gas that escapes into the air) shifts toward ammonia. The higher the pH and the warmer and wetter the manure, the more ammonia volatilizes. Research in poultry houses has confirmed that ammonia concentration in the excreta depends directly on pH, moisture content, and the age of the birds.³

This relationship creates a feedback loop. As uric acid decomposes into ammonia and the pH rises, even more ammonia escapes, which can harm bird health and degrade air quality for workers. The ammonia lost to the air also represents nitrogen that is no longer available as fertilizer when you eventually spread the manure on a field. A chicken house with unchecked pH in the litter can lose a significant fraction of its nitrogen to the atmosphere before the manure ever reaches the soil.

When poultry manure is applied to fields and then leached by rain, it can also shift the chemistry of deeper soil layers. A leaching column study found that poultry manure applications resulted in substantial increases in calcium, magnesium, potassium, sodium, aluminum, ammonium, and nitrate in the water draining through the soil profile.¹¹ Those nutrient pulses can affect soil structure and acidity well below the surface.

Using Alum to Lower Manure pH

Because high pH drives ammonia loss and its associated problems, poultry producers have long looked for ways to bring manure pH down. The most widely studied approach is adding aluminum sulfate, commonly called alum, directly to the litter in poultry houses. Alum is acidic, and when mixed into litter it lowers pH enough to convert ammonia gas back into ammonium, a form that doesn’t volatilize.¹²

The practice has been studied extensively. Field trials showed that alum applications lowered litter pH, with the most pronounced effect during the first three to four weeks of each growout period. Beyond reducing ammonia loss, the alum-treated litter also had lower water-soluble phosphorus, which is a major concern for runoff pollution when litter is spread on fields.¹³ On-farm evaluations confirmed these findings: alum decreased litter pH and the water solubility of phosphorus, arsenic, copper, and zinc.¹⁴

The lower pH also helps with biosecurity. Pathogen numbers tend to decrease in more acidic litter, giving producers an additional incentive beyond nutrient management.¹² For backyard flock owners dealing with ammonia smell or planning to compost litter for the garden, this is worth knowing: if the litter smells strongly of ammonia, the pH is probably too high, and acidifying amendments can help preserve nitrogen and reduce odor.

How Chicken Manure Changes Soil Biology

Beyond the direct pH effects, chicken manure reshapes the microbial communities in soil in ways that matter for plant health and environmental outcomes. An analysis of camphor tree forests fertilized with chicken manure found that bacterial diversity in the soil and root zone was significantly higher in fertilized plots compared to unfertilized ones.¹⁵ The diversity of antibiotic-resistance genes in the soil also increased in fertilized areas, a concern that has drawn growing attention as antibiotic use in poultry production is scrutinized.

pH is one of the strongest drivers of soil microbial community composition, so when chicken manure shifts soil pH, it’s simultaneously opening niches for some microbes and closing them for others. The composting process itself illustrates this: fungal communities during chicken manure composting were primarily shaped by pH, nitrate, and total organic carbon, while bacterial communities responded more to total nitrogen, ammonium, temperature, and the carbon-to-nitrogen ratio.⁴ The pH of the manure or compost is not just a number on a test strip; it’s a master switch influencing which organisms thrive and what biochemical processes dominate.

Practical Guidance for Gardeners and Small Farmers

If you are adding chicken manure to a garden or small farm field, a few practical points follow from the science. First, expect a short-term rise in soil pH, especially in the top few inches. If your soil is already alkaline and you are growing acid-loving crops like blueberries, fresh chicken manure could temporarily push conditions further from what those plants prefer. On the other hand, if your soil tests acidic, chicken manure can provide a modest liming effect while also delivering nitrogen, phosphorus, and potassium.

Second, composting the manure before application moderates the pH swings. Finished compost has already lost much of its volatile ammonia and has a more stable, near-neutral pH. It also reduces the risk of nitrogen burn on plants and brings pathogen levels down. If you are composting chicken litter that includes wood shavings or straw, the carbon in the bedding helps balance the nitrogen-heavy manure and absorbs some of the alkalinity.

Third, keep an eye on the long game. Repeated annual applications of chicken manure, especially at high rates, can gradually acidify soil through the nitrification pathway even though each fresh application temporarily raises pH. Soil testing every year or two is the only reliable way to track where your pH is headed, because the net direction depends on your soil type, rainfall, and how much manure you are putting down.

Finally, if you manage a backyard flock and are dealing with ammonia smell in the coop, the pH of the litter is almost certainly part of the problem. Acidifying amendments like small amounts of aluminum sulfate, or simply more frequent litter changes, can knock the pH down enough to reduce ammonia volatilization and keep the coop more comfortable for both you and the birds.

Comparing Chicken Manure to Other Livestock Manures

Chicken manure is generally more alkaline than cattle or horse manure. Ruminant manure, which has been through a complex four-stomach digestion process, tends to land closer to neutral, often in the 6.5 to 7.5 range, because much of the nitrogen is already in a more stable form and the calcium load is lower. A comparative study of organic manures found that chicken manure and goat dung raised soil pH to 8.3 and 8.4, respectively, compared to a baseline of 8.2 in unfertilized soil, while the combination of all manures actually lowered it to 7.6.¹⁶

Chicken manure also tends to be “hotter” than other manures, meaning higher in nitrogen relative to carbon. That higher nitrogen content is exactly why it releases so much ammonia and has that characteristic strong pH push. Horse manure, by contrast, is bulkier, more fibrous, and lower in nitrogen per unit of weight, so its pH effects on soil are milder. If you have a choice of manures and your soil is already alkaline, horse or cattle manure is typically the safer bet for avoiding further pH increases. If your soil is acid and could use a boost, chicken manure gives you fertilizer and a mild liming effect in the same wheelbarrow load.