State-Of-The-Art-Soil

NEWS FEATURE JEFF HUTCHENS/GETTY

Biochar — a soil additive made by heating biological material — is catching attention as a means to improve crop growth and clean up contaminated water. STATE-OF-THE-ART SOIL A charcoal-rich product called biochar could boost agricultural yields and control pollution. Scientists are putting the trendy substance to the test.

BY RACHEL CERNANSKY

or more than 150 years, the Brooklyn Navy Yard increasing their yield, and he hopes for more impressive constructed vessels that helped to stop the slave trade results over the next few years. from Africa, lay the first undersea telegraph cable Across the United States, sales of this long-lasting soil F and end the Second World War. Now, this sprawling additive have surged over the past few years, tripling annually industrial facility in New York City is filled with artists, since 2008, according to some estimates. The Biochar Com- architects, producers of artisanal moonshine and people pany in Berwyn, Pennsylvania — which supplied Flanner’s growing organic vegetables. On a drizzly day in autumn, Brooklyn farm — sells it both wholesale and direct to con- Ben Flanner tends a sea of red and green lettuce on a sumers, through outlets including Amazon and some Whole 6,000-square-metre rooftop farm. Foods stores. And countries ranging from China to Sweden The soil beneath the plants looks ordinary, but Flanner are using biochar on agricultural fields and city lawns. grabs a handful and holds it up for inspection. Amid the Proponents see big potential for the soil enhancer, which brown clods of dirt are small black particles — remnants of is produced by heating biological material — such as husks charcoal fragments that were mixed into the soil two years and other agricultural waste — in a low-oxygen chamber. ago. Flanner thinks that this carbon-rich material, known Biochar can be made as a by-product of biofuel generation, as biochar, has helped the crops to thrive, possibly even so some companies are hoping to cash in on both products

258 | NATURE | VOL 517 | 15 JANUARY 2015 © 2015 Macmillan Publishers Limited. All rights reserved FEATURE NEWS as demand grows for greener forms of energy. these convoluted pathways help to slow down improper applications of biochar. In some of the Interest in biochar is also growing among drainage in sand and speed it up in clays. studies that showed decreases in yields, he says, scientists, who are quickly ramping up stud- That is significant, Barnes says, because even the soils were perfectly fine to start with. Other ies to test its potential. They are particularly though clays can hold large amounts of water, work suggests7 that using the wrong type of bio- interested in how the chemical and physical that moisture has a hard time moving through char can negatively impact the soil’s microbiota properties of biochar particles affect water the grains and reaching plant roots. Some stud- or, potentially, its carbon-storage capacity. A moving through soil, remove pollutants, alter ies have shown that plants grow better in soil biochar made from rice straw, for example, will microbial communities and reduce emissions function differently in a certain soil than will of greenhouse gases. The hope is that biochar biochar made from wood or manure. can help farmers around the world, particu- Overall, however, the positive impacts of bio- larly those in Africa and other developing char seem to outweigh the negative ones. A 2011 regions, who often struggle with poor soils. THE HOPE IS THAT meta-analysis8 found an overall average yield Johannes Lehmann, a crop and soil scientist increase of 10%, rising to 14% in acidic soils. at Cornell University in Ithaca, New York, says BIOCHAR COULD Biochar’s greatest potential might be in places that different types of biochar “have unique where soils are degraded and fertilizer scarce, potential to mitigate some of the greatest soil- in part because it helps the soil to better retain health constraints to crop productivity — for HELP FARMERS, any nutrients that it does have. Andrew Crane- example, in highly weathered and sandy soils”. Droesch at the University of California, Berke- But there are still many questions about PARTICULARLY IN ley, has been studying the impacts of biochar in biochar, particularly in terms of making sure such degraded soils in western Kenya. His pre- that it is affordable and has positive effects. In AFRICA AND OTHER liminary data suggest that farms using biochar some studies, the material has actually reduced averaged 32% higher yields than controls. yields. Part of the difficulty is that biochar can In June, a World Bank report9 said that be produced from all kinds of biomass and at DEVELOPING REGIONS. biochar probably holds the most potential for different temperatures and speeds, which leads small farmers in developing countries, not just to huge variation in the substance — and in because they are working with the soils most results. “I always say we should not even use with added biochar than in plain soils or those likely to benefit, but because biochar may be the singular for biochar,” says Lehmann. treated just with compost2. a key element of ‘climate-smart’ agriculture “There are only biochars.” Researchers are also teasing apart how — practices that both help to mitigate climate biochars influence microbial activity in soil. change and reduce vulnerability to its effects. AMAZONIAN ROOTS Microbes typically act as a community; for Although it is just starting to catch on with example, many pathogenic bacteria attack a POLLUTION WRANGLER farmers today, biochar has ancient roots. Hun- plant’s roots only when they have sufficient Biochar’s start may have been in agriculture, dreds to thousands of years ago, residents of numbers to overwhelm the host’s immune but researchers are now looking at other appli- the Amazon produced it by heating up organic response. Caroline Masiello, a biogeochemist cations. Biochar can bind to heavy metals in soil, matter to create rich, fertile soils called terra at Rice University in Houston, Texas, and her which helps to keep them from reaching plants preta. But the practice was abandoned around co-workers have found3 that biochar can inhibit or entering water supplies. That has attracted the time that European nations invaded South this by binding to the signalling molecules that the notice of the US Environmental Protection America, and relatively few farmers elsewhere bacterial cells secrete to coordinate their activity. Agency, other agencies, and companies seek- have routinely used biochar. Scientists first took “They all think they’re alone, because the ing to reclaim land formerly used in mining. At a big interest in the material about a decade ago, telephone wires have been cut,” says Masiello. the Hope Mine near Aspen, Colorado, biochar when growing concerns over global warming With further research, she says, it might be added in 2010 helped to neutralize the impacts led some to tout biochar as a way to store huge possible to fine-tune this function of biochar of decades-old mine refuse by immobilizing the amounts of carbon underground. Hope for that to reduce plant infections. metals and increasing the amount of water held application has faded somewhat, but soil scien- Other researchers are exploring how biochars on the slope — thereby reducing the opportu- tists are now exploring its use in agriculture and can cut emissions of nitrous oxide, a greenhouse nity for contaminated water to become run-off. remediating pollution. gas, from agricultural fields. Last year, Xiaoyu It also helped to spur plant growth on the for- A particular focus has been explaining how Liu, a soil scientist at Nanjing Agricultural Uni- merly barren hillside, according to the Aspen biochar affects water movement through soils. versity in China, and his colleagues reported4 Center for Environmental Studies. Rebecca Barnes, a biogeochemist at Colorado that after biochar had been applied to maize Biochar is also showing promise in cleaning College in Colorado Springs, and some of her (corn) and wheat fields once, nitrous oxide up polluted water, perhaps as a much cheaper colleagues tested that by adding biochar to dif- emissions declined over the following five crop replacement for activated charcoal, which is ferent materials1. In sand, through which water seasons, a period of three years. Other studies used at sites ranging from treatment plants to typically drains very quickly, biochar slowed the have shown reductions as well, but research- areas that are heavily contaminated with toxic movement of moisture by an average of 92%. ers have not yet been able to determine what chemicals. Biochar particles have a relatively In clay-rich soil, which usually retains water, exactly causes this effect. Applying biochar large surface area, which expands even further biochar sped up movement by more than 300%. “can also improve some soil properties, like it in water, providing a vast number of sites for The researchers suggest that the biochar can increase the potassium availability, and the contaminants to bind to, says Charles Pittman, alters how water moves through the interstitial soil organic-matter content”, says Liu, who has a retired chemist at Mississippi State University space — the gaps between grains in the soil. obtained some funding from biochar producers. in Starkville. He says that this type of pollution “Clays tend to be flat grains and sand tends But not all studies show biochar to be a won- remediation may be particularly beneficial in to be circular grains, but biochar is very amor- der material. In some cases it has reduced crop countries that lack full water-treatment sys- phous — and so it’s not only creating these crazy yields5, and one study6 suggests that it lowers tems. It could also help to remove antibiotics or pathways through the biochar, but it’s also cre- the activity of plant genes that help to defend chemical wastes, which are difficult to strip out ating crazy pathways in that interstitial space,” against insect and pathogen attacks. with conventional water treatments. says Barnes. She and her colleagues suggest that Lehmann says that this may come down to Scientists have even explored biochar’s

Workers at the Villa Carmen Biological Station in Peru turn soil containing black flecks of biochar, produced by burning bamboo in metal drums. potential for treating fluids used in oil and pushing animal manure, but neither may be the for his soils over the long term because it helps gas drilling, and as a component of print ton- most efficient way to produce it on a massive them to retain nutrients and water. “Those are ers and paint products. “There’s a lot of other scale. And using wood could spur deforestation both very important, especially in such a well- markets that haven’t fully been explored yet,” or harmful land-use practices. drained soil as on a green roof,” he says. “We says Kurt Spokas, a soil scientist with the US “It’s an incredibly important question to ask: tend to lose both of those quickly.” Department of Agriculture’s Agricultural what is the sustainability of the feedstock?” But before he adds more of the black grains Research Service in St Paul, Minnesota. says Alfred Gathorne-Hardy, research director to other parts of his farm, he will wait to see Experts caution, however, that it is not clear of the India Centre for Sustainable Develop- how the crops respond over the next few years. when or whether remediation — or other appli- ment at the University of Oxford, UK. “This Like the scientists studying biochar, he is eager cations — will be economical, particularly in is the kind of debate I don’t think we’re seeing to see whether it will live up to its bright prom- agriculture. Poor soils and poverty often go enough about within the biochar world.” ise or fade like so many other would-be won- together. After demonstrating yield increases in der materials. ■ Kenya, Crane-Droesch looked at the economic GROWTH INDUSTRY viability of biochar in the same communities. That debate may grow as consumer interest Rachel Cernansky is a freelance writer in “What we found was almost nobody was will- does — something that is slowly happen- Denver, Colorado. ing to pay for biochar when offered at roughly ing around the world. Björn Embrén, who 1. Barnes, R. T., Gallagher, M. E., Masiello, C. A., Liu, Z. the price it took to make it,” he says. is responsible for tree planning and protec- & Dugan, B. PLoS ONE 9, e108340 (2014). Biochar prices vary widely, but in the United tion in Stockholm, says that the city has been 2. Liu, J. et al. J. Plant Nutr. Soil Sci. 175, 698–707 States some products cost US$3 per kilogram, using biochar to boost local vegetation since (2012). comparable to certain fertilizers and more than 2009; he credits it with the city’s healthiest tree 3. Masiello, C. A. et al. Environ. Sci. Technol. 47, 11496–11503 (2013). many composts. On a large scale, biochar pro- growth in recent years. In September, the New 4. Liu, X. et al. Agric. Syst. 129, 22–29 (2014). duction may make economic sense only when York-based charity Bloomberg Philanthropies 5. Rajkovich, S. et al. Biol. Fert. Soils 48, 271–284 biofuel production does — for example if it is awarded Stockholm €1 million (US$1.2 mil- (2012). subsidized or because policies to reduce carbon lion) to launch a city-wide programme that 6. Viger, M., Hancock, R. D., Miglietta, F. & Taylor, G. GCB Bioenergy http://dx.doi.org/10.1111/ emissions drive fossil-fuel prices up. will turn residential garden waste, and eventu- gcbb.12182 (2014). And if demand ever does surge, there will ally food waste and even sewage, into biochar. 7. Zimmerman, A. R., Gao, B. & Ahn, M.-Y. Soil Biol. be questions about the environmental impact Back in Brooklyn, Flanner continues to Biochem. 43, 1169–1179 (2011). of producing biochar. One key concern is the monitor his crops. The lettuces and carrot 8. Jeffery, S., Verheijen, F .G. A., van der Velde, M. & Bastos, A. C. Agric. Ecosyst. Environ. 144, 175–187 choice of feedstock. China is eager to use agri- tops glisten under the rain as he steps care- (2011). cultural waste, such as rice and wheat straw, and fully between rows in his bright yellow rain 9. Scholz, S. M. et al. Biochar Systems for Smallholders some researchers in the United States are even jacket. He thinks that the biochar will be good in Developing Countries (World Bank, 2014).