ARS | Publication request: Characteristics and nutrient values of biochars produced from giant reed at different temperatures

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2012
Publication Date: January 10, 2013
Citation: Zheng, H., Wang, Z., Deng, X., Zhao, J., Luo, Y., Novak, J.M., Herbert, S., Xing, B. 2013. Characteristics and nutrient values of biochars produced from giant reed at different temperatures. Bioresource Technology. 130:463-471.

Interpretive Summary: In soils with meager carbon and nutrient levels, biochar application has been proposed as a method to improve their quality for higher crop yields. Biochar is produced by pyrolyzing raw plant feedstocks at temperatures between 300 to 700 degrees Celsius under a low oxygen environment. Most often, timber, crop residues, weeds, or a wood byproduct serve as the raw feedstock for biochar production. Unfortunately, less is known about the impact of pyrolysis temperature on biochars elemental composition and its ability to release soluble nutrients for crop uptake. This study examined the effects of a range of pyrolysis temperatures from 300 to 600 degrees Celsius on biochars elemental composition and the content of water soluble plant nutrients. Giant reed [Arundo donax L.], a common weed in China, served as the raw feedstock. We found that biochars produced at pyrolysis temperatures greater than 400 degrees Celsius had lower amounts of structural nitrogen and less soluble nitrogen was released. On the other hand, phosphorus and potassium contents in biochars were not affected by pyrolysis temperature. Our results show that if a nutrient-rich biochar from Giant Reed is needed for soil fertility improvement, then the reed should be pyrolyzed at temperatures less than 400 degrees Celsius.

Technical Abstract: Application of biochars to soils is suggested as an effective way for improving soil quality. To investigate the effect of pyrolysis temperature on properties and nutrients value, biochars were produced from giant reed [Arundo donax L.] at 300-600 degrees Celsius and characterized for their physical and chemical properties, release of nitrogen, phosphorus, potassium, and soluble nitrogen and phosphorus adsorption. With increasing pyrolysis temperatures, more nitrogen was lost in emitted gasses and residual nitrogen was transformed to heterocyclic nitrogen, whereas no phosphorus and potassium losses were observed. Phosphorus was transformed less soluble minerals, resulting in available-phosphorus reduction for high-temperature biochars. More soluble ammonium, phosphorus and potassium were released in water from all the biochars at pH less than 5. Low-temperature biochars pyrolyzed at less than 400 degrees Celsius showed appreciable ammonium adsorption. These results indicate that pyrolysis at low-temperatures may be optimal for producing biochar from giant reed to improve the nutrient availability more suitably in acidic soils exhibiting nitrogen, phosphorus and potassium deficiencies.