WASHINGTON, June 23, 2016 - When biomass is heat-treated using a process called torrefaction, the result is a charcoal-rich substance called biochar. This “torrefied biomass” can improve the quality of poor soil found in arid regions, says a study conducted by researchers at Japan’s RIKEN Center for Sustainable Resource Science and recently published in the journal Scientific Reports

The researchers added torrefied plant residual biomass from the biodiesel crop Jatropha curcas into aridisol, a type of soil that dominates deserts and occupies about one third of the Earth's land surface. Aridisols have a very low concentration of organic matter– and water deficiency is its major defining characteristic. An important quality of good soil is its ability to retain water.

The researchers’ tests showed that water retention increased with the percentage of torrefied biomass, with 5 percent biomass yielding a soil that contained about 5 percent more water than the control soil.

A good soil also remains structurally sound deeper in the ground where pressure from above is higher. Soil treated with 5 percent torrefied biomass showed significantly higher levels of compression stress than the control soil, say the researchers, and significantly shorter relaxation time – the time needed for it to relax back into its normal shape after being compressed. 

The team also tested the chemical properties of the soils. They found that levels of potassium, sodium and phosphorous, three elements that plants regularly take up from soil, were higher in the soil treated with the torrefied biomass. Levels of organic acids and bacteria that promote plant growth were also higher in the treated soil, supporting the idea that torrefied biomass can enhance soil fertilization, say the researchers.

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Plants grown in the torrefied biomass had thicker stems, much longer roots and were heavier than those grown in the untreated soil.

“Jatropha is a potential biomass resource for dryland African landscapes, but the poor climate and soil conditions have limited its production,” says team leader Jun Kikuchi. “Our study shows that treating the poor soil with torrefied biomass improves a variety of factors that ultimately lead to greater plant growth.”

“Our next step,” says Kikuchi, “is to elucidate the complicated reactions between symbiotic microbiota and plants for effective growth in nutrient-poor environments.”


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