Getting the carbon-to-nitrogen ratio right when composting manure


Manure and livestock go hand in hand. Manure can be considered a by-product or waste, or it can be an important soil nutrient source. Andrea Stroeve-Sawa of Shipwheel Cattle Feeders is a seasoned composter, following in the tradition of composting feedlot manure her dad started almost 40 years ago.

Andrea’s dad was also talking about soil health before it was a prominent topic, and now both of them are learning all the terms behind the science on their operation. One phrase that sticks out that applies to both soil health and composting is the carbon to nitrogen ratio (C:N) and understanding the interaction between the two elements.

Shipwheel Cattle cleans out their pens in May and puts the manure into windrows, on a clay-lined compost pad. “We try to make sure that it’s a proper balance of manure and bedding,” says Stroeve-Sawa in a recent RealAg LIVE!

When the compost pile gets up to 150 degrees, it’s time to turn it — typically three to five times a cycle. The whole process takes six to eight weeks and then the finished compost gets transported to neighbouring potato, onion, and high-value wheat farms.

That balance of manure and bedding, and the amount of moisture are all key to a healthy compost pile. “The more straw you have, the higher it is in carbon and then the more nitrogen you have, the higher it is in manure,” says Stroeve-Sawa.

Straw itself generally has a high C:N — for example, wheat straw has a C:N of 80:1, so 80 parts carbon to one part nitrogen. The higher the amount of carbon in the bedding, the longer it will take for microbes to break that residue down. Generally, microbes need a food source that has a C:N of 24:1, and if there’s a high amount of bedding with a high C:N in the compost pile, the microbes have to find a nitrogen source. In the case of manure composting, that nitrogen source is the manure itself — microbes can use that nitrogen to fuel the decomposition of carbon in the bedding.

Turning that pile is so important because the microbes need a replenished source of oxygen. As those microbes decompose the bedding component of the pile, they use up oxygen and produce carbon dioxide. If not enough oxygen is supplied, the process becomes anaerobic, and the compost pile starts producing undesirable smells.

The final result of a balanced, productive composting process should be a very stable, volume-reduced, rich soil amendment.

You can catch the whole conversation featuring Andrea Stroeve-Sawa on this RealAg LIVE!

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