Chicken manure undergoes a rapid chemical change that shifts its acidity level soon after excretion. Fresh chicken droppings are initially slightly acidic or close to neutral, typically registering a pH around 6.0 to 7.0. The common perception of chicken waste is that it is highly alkaline, and this is because the waste quickly transitions to a strongly basic state as it decomposes. This rapid shift, often reaching a pH between 8.0 and 9.0, is driven by the breakdown of uric acid into ammonia.
The Chemical Components Driving pH
The initial acidity of fresh chicken droppings is primarily due to uric acid, which is the main form of nitrogenous waste in birds. Unlike mammals, which excrete urea in liquid urine, chickens excrete a semi-solid waste containing this organic acid compound. Uric acid accounts for a large percentage of the total nitrogen present in the fresh waste.
The swift transformation to an alkaline state is a microbially mediated process that begins almost immediately upon excretion. Enzymes like uricase, produced by bacteria present in the litter, break down the uric acid molecule. This decomposition releases ammonia gas, which is a strong base. The liberation of ammonia rapidly consumes hydrogen ions, causing a dramatic increase in the pH of the litter mixture.
As the litter ages, the pH can climb significantly above 8.0. This high alkalinity makes fresh chicken manure potent and potentially damaging to plants. The physical composition of the waste also contributes to its basic nature, as it contains high concentrations of minerals, particularly calcium.
These mineral components act as a liming agent when the manure is applied to soil. The presence of these basic salts counteracts soil acidity over the long term. The combination of the initial ammonia release and the high mineral content ensures that aged chicken manure maintains a moderate to strong alkaline profile.
Factors That Alter Manure pH
The eventual pH of the chicken litter mixture is heavily influenced by external factors, starting with the chicken’s diet. A high-protein feed results in higher levels of nitrogenous waste, which leads to a more rapid spike in ammonia production and alkalinity. Mineral supplements, such as calcium added for eggshell production, also directly increase the content of basic compounds in the waste.
The type of bedding material used in the coop significantly affects the overall pH balance of the collected litter. Materials like wood shavings or straw are mixed with the droppings and serve as a carbon source. These materials can initially buffer the pH, preventing it from rising too quickly.
Environmental conditions, particularly moisture and ventilation, are critical factors in the rate of chemical conversion. High moisture content accelerates microbial activity, speeding up the production of alkaline ammonia and leading to a faster pH spike. Poor ventilation traps the released ammonia gas, contributing to the high pH of the litter surface and causing nitrogen loss into the atmosphere.
Using Chicken Manure Safely in the Garden
The highly alkaline nature and concentrated nitrogen content of fresh chicken manure necessitate stabilization before use as a soil amendment. Applying fresh litter directly causes “nitrogen burn.” The volatile ammonia gas damages plant roots and foliage, often leading to plant death. Therefore, composting or aging the material is required for safe use.
Composting is the most effective method for managing high alkalinity and ammonia content. The process involves creating a hot, aerated environment where microorganisms break down complex organic compounds. Proper hot composting requires the pile to reach 130 to 150 degrees Fahrenheit, which destroys pathogens and drives off excess ammonia. This step converts volatile nitrogen into stable, organic forms that plants can safely utilize.
During composting, the pH gradually stabilizes as ammonia off-gasses and the organic matter matures. The finished compost is a dark, crumbly material with a pH much closer to neutral, making nutrients safely available. This well-aged manure acts as a slow-release fertilizer and provides organic matter to improve soil structure.
Safe Application Guidelines
Gardeners must never use fresh chicken manure in growing beds. When using aged or composted manure, follow these guidelines:
- Blend the manure thoroughly into the soil, rather than leaving it as a top dressing, to prevent potential root damage.
- A general application rate for fully aged manure is approximately 45 pounds per 100 square feet, worked into the top six inches of soil.
- Apply the composted manure at least 90 to 120 days before harvesting any root crops.
- Avoid applying composted manure close to the harvest time of leafy greens that come into contact with the soil.