Before we knew what nutrients are essential for plant growth, early farmers were using animal manure from livestock to fertilize their cropland. Manure has been the main fertilizer source for most of recorded history. It wasn’t until the mid-1900s that chemical fertilizers became the mainstay for fertilization practices.
Despite the availability of chemical fertilizers, manure remains a popular fertilizer source for organic farmers, backyard gardeners, and commercial gardeners alike. Amending the soil with manure has many added benefits aside from being a fertilizer source. If you live close to livestock owners, you may even be able to get manure for free. Let’s examine and the ins and outs of using nature’s fertilizer.
First, we need to know the source. When using manure on sites for growing edible crops, manure should be sourced from livestock such as dairy or beef cows, horses, rabbits, goats, or sheep. Avoid animal waste that could contain pathogenic micro-organisms, such as waste from pigs, cats, or dogs. Also, avoid manure collected from livestock that graze on pastures treated with herbicides. Certain herbicides remain active even after they have passed through the animal’s digestive system.
Second, manure should be properly aged or composted to minimize contamination of fresh produce or burning plants from excess fertilizer salts. This means that most manures should be aged for at least 6 months or be hot composted. Hot composting involves holding the compost between temperatures of 131 F and 170 F for a specific time. This method of composting has the added benefit of reducing potential weed seeds that could be present in livestock manure.
Third, manure will supply essential nutrients to plants, but additional fertilizers may be needed. When compared to chemical fertilizers, manure is relatively low in the big three nutrients most needed by plants – nitrogen, phosphorus, and potassium. While it will supply these essential nutrients, the needs of the crop being grown will likely mean additional fertilizer, either from organic or chemical fertilizers, will need to be used. The table provided lists how many pounds of nitrogen, phosphorus, and potassium are supplied per 100 pounds of aged or composted manures from common livestock sources. Additionally, composted manure acts more as a slow-release fertilizer and will not supply a quick release of nutrients to plants.
While manure alone may not sufficiently supply all the nitrogen, phosphorus, and potassium a crop will need to be most productive, it has other benefits for improving growing conditions. Incorporating manure into the soil is one of the best ways for adding organic matter to our gardens. Organic matter tends to decompose quickly in heavily worked soils as well as soils in hot, humid environments.
Additionally, organic matter is important for improving soil structure. Soils that are heavy and poorly drained can be improved through incorporation of organic matter. Soils that are sandy, lacking the ability to retain water and nutrients, benefit from added organic matter. Additions of organic matter also support healthy microorganism activity in the soil, such as earthworms and nitrogen fixing bacteria, which aid in plant growth and production.
We tend to place heavy demands on our garden soil. Using composted manure from livestock can improve the health of our garden soil by boosting organic matter content, reducing the demand for excess chemical fertilizers, and improving soil fertility. Just remember to use a known source of manure that has been properly aged or composted and incorporate it into the garden soil before planting.
It is good practice to have your garden soil tested every two to three years to evaluate what nutrients need to be adjusted along with the soil pH. Samples of composted manure can also be sent to certified testing labs for nutrient analysis or testing for herbicide residues if you are uncertain of the source. Let me know if you have questions about how to summit samples.
