Chicken manure is a highly valued organic fertilizer, recognized for its potent concentration of plant nutrients, including nitrogen, phosphorus, and potassium. It is an effective soil amendment for improving fertility and structure. Understanding its chemical properties, particularly its pH level, is crucial for safe and effective application. Knowing whether this fertilizer is acidic or alkaline helps prevent plant damage and ensures proper nutrient balance in the soil.
The Alkaline Nature of Chicken Manure
Chicken manure is consistently characterized as alkaline, or basic, and has a significant capacity to raise soil pH. Fresh poultry litter often exhibits a pH between 7.5 and 9.0, making it moderately to strongly alkaline. This high pH results directly from the chemical composition and the rapid breakdown of nitrogenous compounds within the fresh material.
The manure’s alkalinity creates a notable “liming effect,” meaning it can reduce soil acidity over time. Aged or properly composted chicken manure, in contrast, has a lower and more stabilized pH. The composting process causes the pH to decrease toward a more neutral range, making it safer for general use.
Composition Driving High pH Levels
The high alkalinity in fresh chicken manure is primarily due to the elevated concentration of nitrogenous waste. Birds excrete nitrogen mainly as uric acid and urea. This highly concentrated nitrogen quickly breaks down through microbial activity.
This decomposition converts urea and uric acid into ammonium, which rapidly converts into volatile ammonia gas, a strong base. The release of ammonia drives the pH level upward and gives fresh manure its pungent odor. Furthermore, the high mineral content of poultry manure also contributes to its basic nature. Poultry feed is often supplemented with calcium, which acts as a liming agent when mixed into the manure.
How Alkalinity Influences Soil and Plant Uptake
Applying fresh, highly alkaline manure directly to a garden can cause immediate negative effects on plant health. The high pH and concentration of volatile nitrogen can lead to “ammonia burn,” which severely damages plant tissues, roots, and seedlings. This volatile nitrogen is also lost to the atmosphere as ammonia, reducing the overall nitrogen content of the fertilizer.
Introducing a highly basic material into the soil can interfere with how plants absorb other nutrients. High soil pH causes certain micronutrients, such as iron, manganese, and zinc, to become chemically “locked up.” When the soil is too alkaline, these elements become insoluble in water, making them unavailable for plant roots. This leads to nutrient deficiencies and stunted growth, especially in soils that are already naturally alkaline.
Stabilizing Manure Through Composting and Curing
To mitigate the damaging effects of high alkalinity and nutrient volatility, chicken manure must undergo a stabilization process, typically through composting or curing. Proper composting involves mixing the nitrogen-rich manure with carbon-rich materials, such as wood chips or straw, to achieve an optimal carbon-to-nitrogen (C:N) ratio, ideally around 30:1. The composting process allows beneficial microorganisms to break down the organic matter.
This microbial action converts the volatile ammonium into more stable, plant-available forms of nitrogen, such as nitrates. This chemical transformation is the process that significantly lowers and stabilizes the pH of the finished compost. A sufficient aging period, often six months to a year, is necessary to ensure the manure is fully cured, resulting in a dark, earthy-smelling product that is safe to apply near plant roots without the risk of burning or excessive soil alkalinity.