Biochar physico-chemical properties as affected by environmental exposure

Giovambattista Sorrenti; Caroline A Masiello; Brandon Dugan; Moreno Toselli

doi:10.1016/j.scitotenv.2016.03.245

Biochar physico-chemical properties as affected by environmental exposure

Sci Total Environ. 2016 Sep 1:563-564:237-46. doi: 10.1016/j.scitotenv.2016.03.245. Epub 2016 Apr 30.

Authors

Giovambattista Sorrenti¹, Caroline A Masiello², Brandon Dugan³, Moreno Toselli⁴

Affiliations

¹ Department of Agricultural Sciences, University of Bologna, viale G. Fanin 44, 40127 Bologna, Italy. Electronic address: g.sorrenti@unibo.it.
² Departments of Earth Science, BioSciences, and Chemistry, Rice University, Houston, TX 77005, USA. Electronic address: masiello@rice.edu.
³ Department of Earth Science, Rice University, Houston, TX 77005, USA. Electronic address: dugan@rice.edu.
⁴ Department of Agricultural Sciences, University of Bologna, viale G. Fanin 44, 40127 Bologna, Italy. Electronic address: moreno.toselli@unibo.it.

PMID: 27135586
DOI: 10.1016/j.scitotenv.2016.03.245

Abstract

To best use biochar as a sustainable soil management and carbon (C) sequestration technique, we must understand the effect of environmental exposure on its physical and chemical properties because they likely vary with time. These properties play an important role in biochar's environmental behavior and delivery of ecosystem services. We measured biochar before amendment and four years after amendment to a commercial nectarine orchard at rates of 5, 15 and 30tha(-1). We combined two pycnometry techniques to measure skeletal (ρs) and envelope (ρe) density and to estimate the total pore volume of biochar particles. We also examined imbibition, which can provide information about soil hydraulic conductivity. Finally, we investigated the chemical properties, surface, inner layers atomic composition and C1s bonding state of biochar fragments through X-ray photoelectron spectroscopy (XPS). Ageing increased biochar skeletal density and reduced the water imbibition rate within fragments as a consequence of partial pore clogging. However, porosity and the volume of water stored in particles remained unchanged. Exposure reduced biochar pH, EC, and total C, but enhanced total N, nitrate-N, and ammonium-N. X-ray photoelectron spectroscopy analyses showed an increase of O, Si, N, Na, Al, Ca, Mn, and Fe surface (0-5nm) atomic composition (at%) and a reduction of C and K in aged particles, confirming the interactions of biochar with soil inorganic and organic phases. Oxidation of aged biochar fragments occurred mainly in the particle surface, and progressively decreased down to 75nm. Biochar surface chemistry changes included the development of carbonyl and carboxylate functional groups, again mainly on the particle surface. However, changes were noticeable down to 75nm, while no significant changes were measured in the deepest layer, up to 110nm. Results show unequivocal shifts in biochar physical and chemical properties/characteristics over short (~years) timescales.

Keywords: Ageing; Charcoal; Density; Imbibition; Porosity; XPS.