Cooking better biochar: Study improves recipe for soil additive

Mar 22, 2012
This is Rice biogeochemist Caroline Masiello. Credit: Jeff Fitlow/Rice University

Backyard gardeners who make their own charcoal soil additives, or biochar, should take care to heat their charcoal to at least 450 degrees Celsius to ensure that water and nutrients get to their plants, according to a new study by Rice University scientists.

The study, published this week in the Journal of , is timely because is attracting thousands of amateur and professional gardeners, and some companies are also scaling up industrial biochar production.

"When it's done right, adding biochar to can improve hydrology and make more nutrients available to plants," said Rice biogeochemist Caroline Masiello, the lead researcher on the new study.

The practice of adding biochar to topsoil to boost crop growth goes back centuries, but in recent years, international interest groups have begun touting biochar's climate benefits as well. Biochar removes carbon from the atmosphere and locks it into the soil for hundreds and sometimes thousands of years.

With companies scaling up production and dozens of do-it-yourself videos online showing how to make biochar at home, Masiello said it is important for scientists to study examine how biochar is produced and learn which methods produce the best biochar.

In their study, Masiello's team learned that when it comes to helping get water to plants, not all forms of biochar are the same. The researchers found produced at temperatures of 450 Celsius or higher was most likely to improve soil drainage and make more water available to plants, while charcoal produced at lower temperatures could sometimes repel water.

Rice's award-winning biochar research group examined the hydrologic properties of biochar produced at various temperatures from three kinds of -- tree leaves, corn stalks and wood chips. For all feedstocks, the researchers found that biochar produced at temperatures above 450 degrees Celsius (842 ) had optimal properties for improving soil drainage and storing carbon.

The research team included Rice undergraduate Tim Kinney, Bellaire High School science teacher Michelle Dean and Rice faculty members, Brandon Dugan, assistant professor of Earth science, and Kyriacos Zygourakis, the A.J. Hartsook Professor in Chemical and Biomolecular Engineering. Other team members were William Hockaday, now an assistant professor of geology at Baylor University in Waco, Texas, and Rebecca T. Barnes, now a visiting assistant professor at Bard College in Annandale-on-the-Hudson, New York.

Making charcoal may sound like a strange way to boost crop production, but the concept was proven more than 2,000 years ago in South America, where native farmers added charcoal to the poor soils of the Amazon rainforest to create a rich, fertile soil known by the Portuguese name "terra preta," or black earth. These modified soils, which are still fertile today, contain as much as 35 percent of their organic carbon in the form of charcoal. Studies over the past decade have found that the charcoal-amended soil holds more water and nutrients and also makes the water and readily available to plants.

The charcoal, or biochar, that is used to create such soil can be made from wood or agricultural byproducts. The key is to heat the material to a high temperature in an oxygen-starved environment. Native Americans did that by burying the material in pits, where it burned for days. Today, industrial-scale biochar production is beginning to occur, and dozens of do-it-yourself videos online show how to make biochar in just a few hours using steel drums.

The agricultural benefits of biochar are just one reason there's a groundswell of interest in biochar production. Some enthusiasts are drawn by a desire to fight global warming. That's because about half of the carbon from , corn stalks and other biomass -- carbon that typically gets recycled into the atmosphere -- can be locked away inside biochar for thousands of years.

"When people mow their yards here in Houston, the carbon from the grass clippings returns to the atmosphere in about six weeks," said Masiello, assistant professor of Earth science at Rice. "We call this carbon-cycling, and it's a universal process. Making biochar is one way to remove carbon from the atmosphere and lock it away for a long time."

Masiello, who specializes in studying the carbon cycle, said the microscopic properties of biochar can vary widely depending upon how it's made. In the worst case, she said, improperly made biochar can harm soil rather than improve it.

"This is the first rigorous study of the hydrologic aspects of biochar," Masiello said. "People often tout the benefits of biochar; it can help clay-rich soils drain better, and it can help sandy soils hold water better. But we are finding that these hydrologic benefits vary widely with biochar production conditions."

She said the study found that biochar produced at temperatures lower than 450 degrees Celsius retained some organic compounds that can actually repel water rather than attract it. In addition, the study found that lower-temperature biochar was a less stable reservoir for carbon and could return significant amounts of carbon to the atmosphere within a few hundred years.

"We plan to study ways to optimize other beneficial properties of biochar, including its ability to remove heavy metals and other pollutants from soil," Masiello said. "Ultimately, we'd like to publish a how-to guide that would show exactly what conditions are needed to produce the optimal biochar for a given situation."

Explore further: Bodies at sea: Ocean oxygen levels may impact scavenger response

More information: www.sciencedirect.com/science/… ii/S0961953412000438

add to favorites email to friend print save as pdf

Related Stories

Biochar: turning waste into wealth

Jun 10, 2009

As all gardeners know, manure helps the flowers grow. But that manure also gives off greenhouse gases, contributing to global climate change.

Can biochar help suppress greenhouse gases?

Apr 20, 2011

Nitrous oxide is a potent greenhouse gas and a precursor to compounds that contribute to the destruction of the ozone. Intensively managed, grazed pastures are responsible for an increase in nitrous oxide emissions from grazing ...

Recommended for you

New feather findings get scientists in a flap

Oct 22, 2014

Scientists from the University of Southampton have revealed that feather shafts are made of a multi-layered fibrous composite material, much like carbon fibre, which allows the feather to bend and twist to ...

Lupin bread rises to the quality challenge

Oct 20, 2014

Sweet lupins are shaping up to be a viable and nutritious element in wheat breads and cereals with recent research suggesting certain varieties produce bread with desirable volume, texture and crumb cell ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

erich_knight
1 / 5 (5) Mar 23, 2012
The Paleoclima­te Record shows agricultur­al-geo-eng­ineering is responsibl­e for 2/3rds of our excess greenhouse gases. The unintended consequenc­e; flowering of our civilizati­on. Our science has now realized these consequenc­es, developing a more encompassi­ng wisdom. Wise land management­, afforestat­ion and the thermal conversion of biomass can build back our soil carbon. Pyrolysis, Gasificati­on and Hydro-Ther­mal Carbonizat­ion are known biofuel technologi­es, What is new are the concomitan­t benefits of biochars for Soil Carbon Sequestrat­ion; building soil biodiversi­ty & nitrogen efficiency­, as a feed supplement cutting the carbon foot print of livestock & in situ remediatio­n of toxic agents, Modern systems are closed-loo­p with no significan­t emissions. The general LCA is: every 1 ton of biomass yields 1/3 ton Biochar equal to 1 ton CO2e, plus biofuels equal to 1MWh exported electricit­y, so each energy cycle is 1/3 carbon negative
erich_knight
1 / 5 (4) Mar 23, 2012
Beyond Rectifying the Carbon Cycle, Biochar systems provide the same healing function for the Nitrogen and Phosphorou­s Cycles

CoolPlanet is gearing up to produce farm scale reactors , on skids, the tank ready fuel can cover all haulage and harvest operations.
CoolPlanet is cool far beyond the $1.00-$1.15 per gallon, because;
There is no fuel blending wall, the more you blend, the lower the C-foot print.
Is it fossil fuel ?...or is it biofuel? ... only your radiocarbon isotope tester knows for sure.

Wee-Beastie Real estate at Land Rush Prices;
The farm scale reactors are producing a high surface area biochar, 600 sq meters / gram, Or, One ton of Char has a surface area of 148,000 Acres!!

CoolPlanetBiofuels' Mike Cheiky presenting to a Google audience his company's plans for "Negative-Carbon" biofuels, soil improvement, and poverty reduction.

http://www.youtub...VlZ9v_0o improvement, and poverty reduct