March 19, 2008 | General

Use What Works? How Novel!

BioCycle March 2008, Vol. 49, No. 3, p. 22
Climate Change Connections
Sally Brown

WHAT is there that isn’t cool about Brazil? First there are those beautiful beaches. And on at least one of those beaches you might just run into that girl from Ipanema, subject of international fantasies for generations. Add to that Lulu da Silva, the progressive President who is riding along a wave of economic prosperity. This wave rests, at least in part, on a decision years back to develop sugarcane-based ethanol. This is the energy efficient kind of ethanol (unlike the corn-based stuff that we here in the U.S. are calling the next best thing since sliced bread). And in the middle of this land of bronzed, energy efficient, economically vibrant perfection, you have the current fantasy of soil scientists across the U.S. – char.
In the soil science community, char is about as hot as you can get. “Char,” also called “bio-char,” is the current politically correct name for charcoal. It is found in high concentrations in the Terra Preta soils in Brazil, which are viewed as a beacon of soil health due to the char content. The source of char in the Brazilian soils is likely burnt municipal solid waste. As these are ancient soils, the wastes were associated with high-density settlements and backyard burnings, rather than a modern day Fresh Kills Landfill fire. Pottery shards in the soils confirm that people and their garbage were the source of the black gold.
Soil scientists and geologists in the U.S. are now looking at char as the answer to all of our problems. Not quite the same as universal health care, but pretty darn close. According to David Laird of the USDA Agricultural Research Service’s National Soil Tilth Lab, char can potentially supply nutrients, increase bioavailability in water, increase soil organic matter, promote nutrient cycling, lower bulk density and increase soil pH. Not only that, there is the potential for char to reduce nutrient and pesticide leaching to groundwater. And you thought charcoal was only good for grilling steaks.
In addition to modern day options of burning landfills, char can be produced through pyrolysis – a thermal conversion process that transforms a range of organic feedstocks into synthetic fuel, oil and char. Pyrolysis is very popular in Europe, receiving the highest level of funding for any alternative energy process. It has been used most successfully with high lignin feedstocks, but there is research on using a wide range of organics as feedstocks for this process. The ratio of the end products is dependent on the temperature and pressure of the reaction.
However, due to the high cost of construction, coupled with some operational difficulties and the energy required to generate that energy, you haven’t yet seen a new pyrolysis plant on every street corner. Pyrolysis may end up being a viable means to produce energy and valuable by-products from a range of organic residuals, but we aren’t there yet. And if we do get there, is the best thing to do with this bio-char to add it to soils or burn it for energy?
Amending soil with burnt residues is not a new practice. For instance, wood ash is added to soils and can be a source of mineral nutrients. This is also the basis for slash and burn agriculture. What is different with char is that it has a much higher carbon content than most types of ash that are more common soil amendments. The combustion process that produces char will volatilize all of the nitrogen, and the high carbon content of the residue will provide adsorption sites for added nitrogen and other nutrients to soils. This will result in nitrogen (N) deficiencies, and potentially others.
Proponents of char recognize that use of this material will require additional N fertilization, and say that the carbon added to soil with char amendments will persist, whereas carbon added from fresh organic matter will rapidly degrade. What is not considered is that carbon added as fresh or composted organic matter will increase productivity of the soils, resulting in better plant growth, higher microbial biomass and so on, that in turn will result in additional carbon being generated and cycled back into the soils. The voice of reason enters the picture. I lose patience with all of this attention to char when perfectly good compost feedstocks continue to go to the landfill.
And this brings me to the central point of this column. We know how to make compost. We know about the benefits of land application of different residuals, including municipal biosolids and animal manures. We know that organic soil amendments can be made in plentiful quantities with simple, low-capital, existing technologies, and they do all of the things that this magic char may be able to do, if there is enough of it and if we can figure out how to land apply it.
Yet, composting and direct land application are not the standard operating practices, but rather the exception. In certain cases it is growing, but in other cases these feedstocks end up in unmanaged piles or landfills with waste management companies calling this a beneficial end use option. Composting and direct land application are simple. They don’t require high pressure or big, engineered structures where lots of things can malfunction. They are not new fangled technologies that engineering firms can make a fortune on. Composting and direct land application are practical, cost-effective and realistic options for the here and now. Research on char has its place. But to me this place is lower on the ladder than research to optimize use of organic amendments.
Research proving the benefits of composting and organics recycling was done decades ago, back before you could get PDF copies of papers, and when PCs were uncommon. Maybe it is time to revisit that research, to bring a deserving spotlight onto uncombusted organics. I am not sure what it will take, perhaps a field trial in Tahiti, or our own girl from Ipanema. But whatever it is, it needs to be done.
Sally Brown – Research Associate Professor at the University of Washington in Seattle – is a member of BioCycle’s Editorial Board, and is authoring this regular column on the connections of composting, organics recycling and renewable energy to climate change. Email Dr. Brown at

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