After 12 weeks, each biocover was evaluated for its effectiveness. The biochar could have a future use as a nutrient-rich soil amendment. Photo credit Brian Dougherty.

Dealing with the smell of animal waste is a challenge livestock producer’s face. That is particularly true for hog production units.

Biochars may help overcome the issue.

“Biochars have unique chemical and physical properties including a highly porous internal structure,” explained Brian Dougherty, Graduate Research Assistant, Ag and Biosystems Engineering. “A few ounces of biochar can have an internal surface area the size of a football field. This makes biochars suitable for a range of environmental applications.

Those applications include hog and dairy farms for odor, gas, and nutrient sorption.

“Research has shown biochar to be effective in adsorbing and retaining nutrients from dairy lagoon effluent,” he wrote. “In one experiment,

When evaluating for a biochar’s effectiveness, the nose knows. Here, Dougherty takes possession of his senses to make observations. Photo credit Brian Dougherty.

biochar enriched with dairy manure effluent reduced greenhouse gas emissions from soil and increased soil carbon and nitrogen storage, said Dougherty. Other research suggests that biochars have the potential to capture excess nutrients from dairy wastewater to create a sustainable nutrient recycling loop. I’m not aware of this sort of research with swine manure, but I don’t see any reason it wouldn’t perform similarly.”

In the case of farm slurries producers have used straw and even flax fibre before, but not always with best results.

What is it that makes this product more suitable?

“That depends on the specific biochar being used,” said Dougherty. “In a 12-week outdoor study, we found that some biochars sank whereas others floated well. It depends on the density of the material as well as how hydrophobic (water repellent) it is. The more it repels water, the longer it will float.

“Conversely, the more it repels water, the less likely it will be to sorb nutrients, so there is a trade-off involved.”

Given the makeup of biochar Doughtery was asked if there was a nutrient advantage when spread on a field?

“Potentially, yes,” he said. “The idea is that the biochar is likely to sorb nutrients while it is floating on top of the lagoon. Given the porous internal structure of biochar, it is more likely to hold onto those nutrients for a longer period of time when applied to soil compared to a straw cover.

“When applied to soil, the nutrient-enriched biochar may serve as a slow-release fertilizer source for plants while improving soils and sequestering carbon. Biochar has the potential to offer other benefits to soil.

“Research has shown that biochars can improve soil productivity, particularly for degraded and lower quality soils by increasing soil pH, water holding capacity, and cation exchange capacity. Biochars are also capable of absorbing organic contaminants, heavy metals, pesticides, and other compounds from the environment due to their complex surface chemistry. In addition, biochars break down very slowly. A portion of the carbon dioxide that was taken in during biomass growth ends up as a very stable form of carbon in the soil.”

The next step in development is to create specific biochars.

“A lot of research is being done with making ‘designer’ biochars, said Dougherty. “The characteristics of a given biochar will vary considerably depending upon what type of biomass it was produced from and what production process was used. This opens up a lot of possibilities for making biochars with the specific properties needed for use as a lagoon cover. Our research found that hydrophobicity, pH, and particle size are important parameters.”

Dougherty said in terms of usages, the potential for biochars is large.

“In addition to an adding it to manure slurry, biochar has been used in silage and other cattle feeds, livestock bedding, and poultry litter (mostly in Europe and Asia),” he said. “The same massive internal surface area and sorption capacity that makes biochar a good soil amendment may also provide benefits when used as a feed additive. It is thought that biochar provides benefits primarily as a toxin binder.

Anecdotal reports indicate that cattle are healthier, milk quality and hoof health is improved, animals have fewer cases of diarrhea, and odors are reduced in barns, offered Dougherty in material sent to this publication.

“Research conducted in Laos found increased rate of gain and reduced enteric methane emissions when biochar was fed to cattle. Research from Australia showed that biochar fed to pastured cows adsorbed nutrients from the cow’s digestive tract and from the manure. I’m not aware of biochar feeding trials being done with swine at this time. It is important to note that biochar is currently not an FDA approved feed additive for any animal that enters the food chain in the United States. Biochar produced for use as a feed additive requires strict quality control and needs to be done with proper certification,” detailed his material.

The cost for biochar is higher at this time. Straw, for example might cost $75-$125/ton depending on location, suggested Dougherty.

Some manure lagoons have a concrete bottom and earthen sides. These are typical on dairies with more solids and bedding, because of the need to drive into the lagoon to clean out the solids on the bottom. It’s especially important on dairies that use sand bedding as it settles out readily. Others have no concrete at all. Photo credit Dan Andersen, Iowa State University.

“The least expensive bulk biochar I have seen for sale is about $400/ton but other prices run much higher,” he said. “Biochar is typically sold by the cubic yard and density can vary quite a bit, so direct comparisons to straw on a mass basis are difficult.

“However, a biochar cover may not need to be applied to the same thickness as a straw cover to achieve the same odor and gas emissions reduction, so again apples-to-apples comparisons are difficult to make. Ideally the other benefits of biochar (nutrient sorption, soil benefits, etc.) would balance out the overall cost vs. benefit analysis.”

There are other benefits to consider too.

Many livestock operations struggle with excess nutrient loads and leaching from farm fields, said Dougherty. “Floating biochar covers could provide a mechanism for passive capture of nutrients with no need for pumps, filters, or additional manure holding tanks,” he reported. “Biochar covers could be blended with the manure and field applied, or collected and sold as a means for exporting excess nutrients off the farm as a high value soil amendment. Despite the challenges, using biochar as a biocover material holds promise, particularly if biochar becomes more readily available as a by-product of bioenergy production. With the proper equipment, it is possible to use excess farm and forestry residue to create biochar on site. Some larger-scale producers are actually making biochar from manure as a means to reduce volume and concentrate nutrients. The biochar production process generates energy that can be used to heat water and warm buildings during colder months. There is also potential for generating electricity, fuels, and other by-products using more sophisticated equipment.”

Dougherty noted in terms of finding the product; “there are many small companies making biochar for local sale. Larger producers are less common. But a few are offering biochar for sale by the semi load. Keep in mind that some of these products are formulated in some way for use as a soil amendment, thus the higher cost compared to raw biochar.” •

— By Calvin Daniels

Photos Courtesy of Brian Dougherty