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Biochar Shows Benefits as Manure Lagoon Cover
USAgNet - 08/10/2017

Manure is a reality in raising farm animals. Manure can be a useful fertilizer, returning valued nitrogen, phosphorus, and potassium to the soil for plant growth. But manure has problems. Odor offensiveness, gas emissions, nutrient runoff, and possible water pollution are just a few.

Timing is also a problem. Livestock produce manure 24/7 -- even when it is impractical or unwise to move it to the field. Delivering manure to the field needs to be timed to nutrient needs, soil moisture levels, and temperature. How can farmers handle this timing issue, as well as other manure problems?

In cities, sewers and water treatment facilities deal with human waste. On farms, manure storage lagoons can hold the manure until the time is ripe. This solves the timing and delivery problem -- but what about odor and gas emissions?

In addition to the inconvenience of odor, manure can release gases connected to air pollution and climate change. Methane, nitrous oxide, ammonia, and hydrogen sulfide are examples. Scientist Brian Dougherty and colleagues researched methods to reduce these negatives while potentially adding some positives: biochar covers.

Biochar is plant matter, such as straw, woody debris, or corn stalks, that has been heated to high temperatures in a low- to no-oxygen environment. The result is a black, carbon-rich material similar to charcoal.

Dougherty says biochar is like a sponge. "Biochar provides a structure with lots of empty pore space" he says. "The outer surface may appear small but the interior surface area is absolutely massive. A few ounces of biochar can have an internal surface area the size of a football field. There is a lot of potential there for holding on to water and nutrients."

In addition to its hidden storage capacity, the surface of the biochar tends to have a chemical charge. This gives biochar the ability to attract and hold nitrogen, phosphorus, and potassium ions, metals, and other compounds. Biochar can also float (some types more than others). That attribute means it can trap gases at the water's surface.

Growing up on a dairy farm, Dougherty is no stranger to the challenges of manure storage. "Once I realized the properties of biochar, I thought it had good potential for a lagoon cover," he says.

Dougherty's research studied two liquid dairy manures with differing nutrient levels. It also studied two types of biochars, made at different temperatures. Biochar is somewhat fickle, showcasing different properties when created at different temperatures. He also included pails of manure with a straw cover for comparison, and au natural with no cover as his control.

The research found that the biochars picked up the most nutrients from the more concentrated manure with a higher nutrient content. "The biochar will take up whatever it can, so if there are more nutrients available the potential for nutrient uptake is greater," Dougherty says. Nitrogen, phosphorus, and potassium are nutrients with the greatest economic value on a farm, but applying them in excess of what the crop can take up can lead to nutrient loss to the watershed.

Dougherty also measured the ammonia at the top of each pail. Ammonia and sulfates are the main source of manure's odor. The cooler-crafted biochar did best here, reducing ammonia by 72-80%. It also floated better. But because it floated better and tended to repel water, it was less effective at attracting and attaching to the nutrients than the warmer-crafted biochar.

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