Why does chicken manure "lose its odor" in a dry chicken coop?

Uncovering the underlying scientific principles: Those who have raised chickens know that fresh chicken manure emits a pungent ammonia odor, which can be particularly unpleasant in humid and stuffy chicken coops. However, have you noticed that when chicken manure is spread out and dried in a dry, well-ventilated area, the odor becomes almost imperceptible after one or two days? This phenomenon is actually governed by a combination of physical and biological principles involving microorganisms, moisture, and odor molecules.

The primary culprit is the "moist microbial factory." The odor of chicken manure mainly originates from two gases: ammonia (resembling a strong toilet odor) and hydrogen sulfide (resembling the smell of rotten eggs). How are these gases produced? Chicken manure contains large amounts of undigested proteins, uric acid, and nitrogen-containing compounds. In a moist environment, these organic substances serve as a "feast" for billions of microorganisms (bacteria and fungi). As these microorganisms decompose the organic matter, they continuously release ammonia and hydrogen sulfide.

Water serves as the key catalyst in this "odor production" process—its presence promotes active microbial proliferation while dissolving chemical compounds in chicken manure, thereby facilitating the decomposition reaction.

Once the environment in the chicked coop becomes dry, the situation immediately reverses: 1. Microorganisms "halt activity." Microorganisms require liquid water for their movement and reproduction. When chicken manure loses moisture and becomes dry chicked coop , hard, or even powdery, microbial metabolism declines sharply, and they may even enter a dormant state. Decomposition reactions nearly cease, preventing the substantial production of ammonia and hydrogen sulfide.

2. Rapid dispersion of residual odor: Even trace amounts of odor are typically dissipated quickly in a dry environment in the chicked coop with adequate air circulation (wind or natural ventilation). Ammonia is highly soluble in water; however, in dry air, it is not "locked" within poultry manure but is rapidly dispersed and diluted, becoming undetectable at a distance of over ten meters.

3. Dust adsorption without irritation: Fully dried chicken manure in the chicken coop transforms into a loose powder. While this powder may adsorb trace amounts of odor molecules, the absence of a continuous emission source results in only a faint "aged ammonia odor" —often described by many as resembling the scent of soil or hay, which is hardly unpleasant.

Why can't we say "absolutely odorless"?

If the environment  in the chicken coop is merely relatively dry (e.g., humidity at 50%), and the chicken manure is piled thickly, moisture may still remain within it. Once nighttime humidity rises or during rainy or overcast weather, the partially moist manure will absorb additional moisture, leading to the "resurrection" of microorganisms and the recurrence of foul odors. Additionally, if dry manure  in the chicken coop is kicked apart and dispersed, trace amounts of odor from the dust may briefly become airborne.

Here's a practical tip for chicken farmers or composters: The simplest way to completely eliminate the odor from chicken manure is to spread it thinly, expose it to sunlight, and ensure proper ventilation. On dry, sunny days, spread the manure evenly into a thin layer 1–2 cm thick and expose it to sunlight for 2–3 days. When touched, it should feel as crisp as a biscuit; by this point, the odor is virtually eliminated, and it can be used directly as base fertilizer or stored in a sealed bag. If a slight odor persists, it's usually because the manure hasn't dried completely—just continue exposing it to sunlight.

Drying is the most cost-effective "deodorant." Understanding this principle reveals that chicken manure can be remarkably "quiet."