Does Cow Manure Have Nitrogen? And How to Use It Safely

Cow manure is a classic organic fertilizer that enriches garden soil. It serves as a source of nitrogen and other nutrients necessary for plant growth. Using this material improves the soil’s structure, enhancing its ability to hold water and support healthy plant development.

Nitrogen Composition of Cow Manure

The nutrient profile of fertilizers is summarized by an N-P-K ratio, representing the percentage of nitrogen (N), phosphorus (P), and potassium (K). For cow manure, this ratio is around 3-2-1, though it can fluctuate. Factors like the cattle’s diet, age, and bedding material like straw or sawdust can alter these values. A high-protein diet, for instance, results in manure with a higher nitrogen content.

Nitrogen within cow manure exists in two primary forms. Fresh manure is high in ammoniacal nitrogen, a volatile, fast-releasing form that can be lost to the atmosphere as ammonia gas. The second form is organic nitrogen, which is more stable and found in aged or composted manure. This nitrogen is released slowly as microorganisms in the soil break down the organic matter.

The distinction between these two forms is important for garden application. While the fast-releasing ammonia in fresh manure might seem beneficial, it is too intense for direct use. The slow-release organic nitrogen in composted manure provides a steady supply of nutrients to plants over a longer period, which helps prevent nutrient runoff.

The Importance of Composting Manure

Using fresh cow manure directly on garden plants poses several risks. The high concentration of ammonia and soluble salts is a primary concern, as it can chemically “burn” plant roots and foliage, leading to damage or death.

Beyond chemical burn, fresh manure contains pathogens that are harmful to humans. Bacteria such as E. coli can be present and can contaminate vegetables, particularly root crops or low-growing leafy greens. If these contaminated vegetables are consumed raw, they can cause serious illness.

Another issue with fresh manure is the presence of viable weed seeds. A cow’s digestive system does not break down all the seeds from the grasses and weeds it consumes. When fresh manure is spread on a garden, these seeds can germinate, leading to a significant weed problem.

Composting is the process that mitigates these dangers. The heat generated within a properly managed compost pile, which should reach temperatures between 131°F and 140°F (55°C), effectively kills most harmful pathogens and destroys weed seeds. This process also stabilizes the volatile ammonia, converting it into the safer, slow-release form of organic nitrogen.

Applying Composted Manure for Nitrogen

Once cow manure has been thoroughly composted, it becomes a safe and beneficial soil amendment. One of the most effective ways to use it is to incorporate it directly into the garden soil before planting. Spreading a layer of composted manure, one to two inches thick, over the garden bed and tilling it into the top six to eight inches of soil enriches the entire root zone.

Another common application method is top dressing, which involves spreading a layer of composted manure around the base of existing plants during the growing season. This technique acts like a mulch, suppressing weeds and conserving soil moisture while providing a continuous, gentle supply of nutrients. As the manure is watered in, the nitrogen and other elements are carried down to the plant’s roots. Care should be taken to leave a small space around the plant stems to avoid smothering them.

For a liquid application, composted manure can be used to create a “manure tea.” This involves steeping a shovelful of composted manure in a permeable bag within a large container of water for a day or two. The resulting nutrient-rich liquid can be used to water plants, providing a gentle boost of nitrogen and other soluble nutrients. This method is particularly useful for giving established plants a mid-season feeding.