Biochar could boost agricultural yields and control pollution

Across the United States, sales of biochar, a long-lasting soil additive, have surged over the past few years. Biochar sales have tripled annually since 2008, according to some estimates. The Biochar Company in Berwyn, Pennsylvania — which supplied Flanner’s Brooklyn farm — sells it both wholesale and direct to consumers, through outlets including Amazon and some Whole Foods stores. And countries ranging from China to Sweden are using biochar on agricultural fields and city lawns.

Proponents see big potential for the soil enhancer, which is produced by heating biological material — such as husks and other agricultural waste — in a low-oxygen chamber. Biochar can be made as a by-product of biofuel generation, so some companies are hoping to cash in on both products as demand grows for greener forms of energy.

Nextbigfuture had reported on the potential for major CO2 mitigation back in 2009 There have been calculations that widespread use of biochar could remove about 1.2 billion metric tons of carbon from the atmosphere each year.

Interest in biochar is also growing among scientists, who are quickly ramping up studies to test its potential. They are particularly interested in how the chemical and physical properties of biochar particles affect water moving through soil, remove pollutants, alter microbial communities and reduce emissions of greenhouse gases. The hope is that biochar can help farmers around the world, particularly those in Africa and other developing regions, who often struggle with poor soils.

Johannes Lehmann, a crop and soil scientist at Cornell University in Ithaca, New York, says that different types of biochar “have unique potential to mitigate some of the greatest soil-health constraints to crop productivity — for example, in highly weathered and sandy soils”.

But there are still many questions about biochar, particularly in terms of making sure that it is affordable and has positive effects. In some studies, the material has actually reduced yields. Part of the difficulty is that biochar can be produced from all kinds of biomass and at different temperatures and speeds, which leads to huge variation in the substance — and in results. “I always say we should not even use the singular for biochar,” says Lehmann. “There are only biochars.”

A particular focus has been explaining how biochar affects water movement through soils. Rebecca Barnes, a biogeochemist at Colorado College in Colorado Springs, and some of her colleagues tested that by adding biochar to different materials. In sand, through which water typically drains very quickly, biochar slowed the movement of moisture by an average of 92%. In clay-rich soil, which usually retains water, biochar sped up movement by more than 300%.

Other researchers are exploring how biochars can cut emissions of nitrous oxide, a greenhouse gas, from agricultural fields. Last year, Xiaoyu Liu, a soil scientist at Nanjing Agricultural University in China, and his colleagues reported4 that after biochar had been applied to maize (corn) and wheat fields once, nitrous oxide emissions declined over the following five crop seasons, a period of three years. Other studies have shown reductions as well, but researchers have not yet been able to determine what exactly causes this effect. Applying biochar “can also improve some soil properties, like it can increase the potassium availability, and the soil organic-matter content”, says Liu, who has obtained some funding from biochar producers.

But not all studies show biochar to be a wonder material. In some cases it has reduced crop yields, and one study suggests that it lowers the activity of plant genes that help to defend against insect and pathogen attacks.

Overall, however, the positive impacts of biochar seem to outweigh the negative ones. A 2011 meta-analysis found an overall average yield increase of 10%, rising to 14% in acidic soils. Biochar’s greatest potential might be in places where soils are degraded and fertilizer scarce, in part because it helps the soil to better retain any nutrients that it does have. Andrew Crane-Droesch at the University of California, Berkeley, has been studying the impacts of biochar in such degraded soils in western Kenya. His preliminary data suggest that farms using biochar averaged 32% higher yields than controls.

Biochar prices vary widely, but in the United States some products cost US$3 per kilogram, comparable to certain fertilizers and more than many composts. On a large scale, biochar production may make economic sense only when biofuel production does — for example if it is subsidized or because policies to reduce carbon emissions drive fossil-fuel prices up.

Applying Biochar on a large scale will require working through environmental and social circumstances.

SOURCES – Nature