Biochar offers little benefit for Ontario farms

Thursday, January 3, 2013

Adding biochar to tropical soils has been shown to have significant benefits for crop production, but the yield benefits with our soil and climate are small or non-existent

by KEITH REID

It was four years ago when I first wrote about biochar in this column. At that time, there was much hype, but little work had been done on the product in soils and climates relevant to Ontario.  How much have we learned since then?

Biochar is any organic material that has been heated with limited oxygen, so the volatile compounds are driven off and what is left is primarily black carbon. This may be done with external heat, or by partially burning the material in a special stove that limits the air supply. The partial burning uses the volatile compounds as the fuel to provide the heat while consuming the oxygen that could have burned the carbon.

Adding biochar to tropical soils has been shown to have significant benefits for crop production. These soils have extremely low capacity for holding nutrients and organic matter is broken down too fast to be useful in improving these soils. So the biochar provides an alternate mechanism for holding nutrients that is stable over a long time period. It also helps to improve moisture-holding capacity in these highly degraded soils.

This situation does not exist for our soils here in Ontario. Even our poorest soils have greater capacity to hold nutrients than tropical soils, and we are not faced with extreme rainfall that leaches nutrients out of the soil. The question, then, is whether there is any benefit at all to adding biochar to agricultural fields in Ontario.

Research trials have shown there can be limited benefits from adding biochar – in some circumstances. The material tends to be alkaline, particularly if it was produced at a low temperature, so acidic soils will benefit from the slight liming effect. Alkaline soils, on the other hand, may show a depression of crop production because the added alkalinity ties up micronutrients.

Biochar also retains many of the nutrients that were contained in the feedstock. This won't be meaningful in a biochar produced from wood or even straw, but a biochar produced from broiler litter will contain significant amounts of phosphorus and potassium (although most of the nitrogen will have been lost). If the soil is deficient in these nutrients, the biochar can be a source to supply the needed fertility.

Note that the charring process does not improve the availability of these nutrients, only that they are retained in the final product. I will leave it to you to decide if this is a good reason for applying a broiler litter biochar, rather than the raw manure.

There are some downsides to biochar that have been identified. The first is that any harmful materials in the charred material will be concentrated, so you want to be sure the raw materials are not high in salts or heavy metals. There are also concerns that some of the byproducts of partial combustion could be toxic to plants or humans at high enough concentrations.

The biggest concern, in my mind, is the economic model that is being used to promote biochar. To summarize the justifications that I have seen, the common thread goes something like this: "There is value to biochar somewhere else along the value chain, so I don't have to show any value for my part of the process. Someone else will pay me for it." Since the destination for biochar is agricultural land, the assumption is that the "someone else" is the farmer.

Given that the yield benefits from biochar with our soil and climate are small or non-existent, it is incomprehensible to me how this business model is sustainable. It is based on a farmer investing $2,500 to $5,000 per acre (at suggested prices and use rates for biochar materials) for something that is not likely to even pay for itself, let alone provide any profit. BF

Keith Reid is manager (Eastern Canada), Soil Nutrient and GHG Management Agriculture and Agri-Food Canada, Guelph