Every few years, age-old practices are rediscovered as “hot” new-age ideas. Then, many burn out and fade to ashes once again. That may be the case with biochar, according to a recent report by the National Center for Appropriate Technology.

Biochar is charcoal produced by burning organic matter such as wood, grasses, crop residues and manure under conditions of low oxygen (pyrolysis). It’s under investigation by the International Biochar Initiative as an approach to carbon sequestration to produce negative carbon dioxide emissions. It’s also being re-explored as a soil amendment and sustainable crop fertilizer replacement.

Research raises sustainable questions
A four-year study at the University of California-Davis showed that the results of adding biochar to productive soils are different from adding it to more weathered, acidic soils, such as those in the tropics. This study used biochar made from walnut shells as an amendment in a plot that rotated tomato and corn crops.

Rather than a change in the nitrogen cycle reported in other biochar studies, this research found that biochar also affected soil potassium, phosphorus and calcium, causing an 8% corn yield increase in the second year of the study. However, benefits declined to nothing by year four.

The researchers concluded that the yield improvement was caused by a direct fertilization effect — one that could also be achieved by other types of fertilizer.

Biochar from different sources might perform differently, conceded the researchers. Longer-term effects to soil may still be unrecognized, so the study will continue.

But is it net climate-friendly?
Biochar has potential to produce farm-based renewable energy — gas or oil, and a carbon soil amendment.

But it’s not climate-friendly, according to the Permaculture Research Institute.

Turning bioenergy crops into buried charcoal to sequester carbon doesn’t work — i.e., produce a net beneficial gain. It releases carbon dioxide to the atmosphere. If done on a massive scale, it could plunge the earth into an oxygen crisis, suggests PRI.