ARS | Publication request: Contributions of pyrogenic materials on the accumulation of soil organic matter

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 8, 2011
Publication Date: April 5, 2012
Citation: Watanabe, A., Uchimiya, M., Ikeya, K., Shindo, H., Hiradate, S. 2012. Contributions of pyrogenic materials on the accumulation of soil organic matter. Japanese Journal of Soil Science and Plant Nutrition. 83:222-227.

Technical Abstract: Soil amendment of charcoal co-product (HHVdb as high as coal) from thermochemical waste biomass-to-energy conversion (slow/fast pyrolysis and gasification) has received considerable interests for both contaminated and agricultural lands. Biochar amendment not only increases soil organic carbon content but offers additional benefits such as higher cation exchange capacity, pH, and nutrient supply (e.g., PKN). Recalcitrant nature of biochar fixed carbon components manifests in their decade-long effectiveness as a soil amendment for target functions along with the carbon sequestration potential. Labile, volatile matter (VM) portion of biochars, on the other hand, can stimulate microbial and plant growths by adding on the existing soil dissolved organic carbon pool. This presentation summarized rigorous biochar characterization (e.g., surface area, functional group, charge, and proximate/ultimate analyses) and sorption-desorption experiments we employ to explore the biochar function, particularly heavy metal stabilization, in different soil types. A series of agricultural waste-derived biochars were produced at 350-800 oC (in 150 oC intervals) and were characterized for the yield, composition (moisture, ash, VM, fixed carbon, and CHNSO), BET surface area, and properties attributable to the surface functional groups (pH, pHpzc, total acidity, and by ATR-FTIR and 1H NMR). Selected biochars were activated to introduce carboxyl, hydroxyl, and phosphate functional groups and to increase the specific surface area. Biochars were then screened for their ability to stabilize heavy metals (Pb, Cu) in soils representing a range of CEC, pH, TOC, and clay content. Biochar amended soils were exposed to a series of desorption conditions to address leaching by rainfall, toxicity characteristics, and in vitro bioaccessibility. Biochars decreased soluble Pb and Cu concentrations relative to the soil-only control without increasing Sb, Al concentrations. Oxidized and phosphorus-rich biochars were the most effective stabilizers, especially on sandy soils that contained Pb primarily in bioavailable oxide and carbonate phases. Overall, biochars can be engineered to improve the carbon sequestration potential as well as the heavy metal stabilization in various soil types by oxidative activation to increase the amount of metal ion-coordinating surface functional groups.