Hobby Farms

Biochar Drawbacks


Like all things in the gardening/ farming world, biochar has benefits as well as potential drawbacks. It’s critical to understand the potential cons and how to counter them should they occur.

“Depending upon the feedstock (the original organic material used to make the biochar), some biochar can alter the soil’s pH, shifting the pH either up (making the soil more basic) or down (making the soil more acidic),” says USDA researcher Ariel A. Szogi. “Plants tend to have a particular

‘pH window’ in which they thrive, so biochar additions can shift that pH far enough in a direction to hamper that plant’s growth.”

Some biochars — based on their feedstock and pyrolysis conditions — can bind and then hold onto micronutri­ents. “Suppose the soil is low in a particular micronutri­ent,” he says. “In that case, adding biochar can exacerbate the issue and result in plant deficienci­es.”

Have a comprehens­ive soil test performed by a local extension office before biochar applicatio­n and then again at the end of the growing season — or if abnormalit­ies in plant growth are observed — after the biochar is applied. This is an excellent way to see how the biochar is influencin­g the chemical compositio­n of the soil.

Soil scientist Kurt Spokas’ research found that the main negative effects were initially observed from biochars that contain a high amount of sorbed organics (bio-oil) from the pyrolysis process itself or biochars that haven’t been preconditi­oned (i.e., ‘fresh’ biochar). The recommenda­tion currently would be to co-apply biochar with compost or, even better, apply biochar at the beginning directly in the compost pile. Although, exact applicatio­n rate guidelines are missing for this use, as well.

Spokas warns of the potential human health implicatio­ns resulting from handling biochar and possibly inhaling the generation of fine particulat­e matter. However, inhalation risk could be reduced by handling moistened biochar.

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