Detection of biochar carbon by fluorescence and near-infrared-based chemometrics

Authors: Uchimiya, Sophie; Franzluebbers, Alan; LIU, ZHONGZHEN - Guangdong Academy; Lamb, Marshall; Sorensen, Ronald - Ron

Submitted to: Aquatic Geochemistry Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2019
Publication Date: 3/19/2019
Citation: Uchimiya, M., Franzluebbers, A.J., Liu, Z., Lamb, M.C., Sorensen, R.B. 2019. Detection of biochar carbon by fluorescence and near-infrared-based chemometrics. Aquatic Geochemistry Journal. 24:345-361. https://doi.org/10.1007/s10498-018-9347-9.
DOI: https://doi.org/10.1007/s10498-018-9347-9

Interpretive Summary: Rapid, easy and inexpensive method is on demand to measure the amount of stable carbon stocks in agricultural soils. This study developed new methods based on infrared and fluorescence-based detection techniques. Developed methods could be used to validate carbon stocks in diverse soil types in the presence of different soil amendments across the United States. These new methods will allow growers, land managers, and policy makers to quantify the carbon stocks on farms.

Technical Abstract: There is a key assumption within the concept of terrestrial carbon sequestration by biochar soil amendment: applied biochar will physically remain on-site for periods exceeding the intended carbon sequestration. Studies are lacking to validate this key assumption, despite known fragmentation and transport tendencies of charcoal black carbon. This study employed fluorescence excitation-emission (EEM) spectrophotometry with parallel factor analysis (PARAFAC) and near infrared spectroscopy (NIR) with partial least square (PLS) regression analyses to trace mm-sized slow pyrolysis biochar applied on a kaolinitic Greenville fine sandy loam during a four-year field trial. Toluene/methanol (1:6 v/v) extracts of surface (0-15 cm) soils afforded a labile and polyaromatic dissolved organic carbon (DOC) fingerprint originating from hydrophilic portions of residual tar/bio-oil on biochar. The % loading of this PARAFAC fingerprint positively correlated (Pearson’s r = 0.5, p < 0.025) with particulate (<53 µm) organic carbon (POC) and nitrogen (PON) and total organic carbon (TOC; <4.75 mm) in bulk soils. The POC increased proportionally to the biochar application rate (0, 11.2, and 22.4, Mg ha-1), and correlated with NIR scattering (in log 1/reflectance at 1100 nm; Pearson’s r = 0.8, p < 0.0005) originating from diffuse reflectance of biochar black carbon. The PLS cross validation statistics indicated the ability of NIR to predict both bulk (TOC, POC) and aqueous-phase properties (pH, electric conductivity, DOC, and %DOC of CaCl2 and pyrophosphate extracts) of biochar amended soils. Greater irrigation rate (from 0, 33, 66, to 100%) enhanced the mobility of biochar-borne DOC. Comparison with a separate field experimental site (Bowling Green, KY) indicated the ability of developed EEM/PARAFAC and NIR/PLS methods to validate biochar’s dissolved and bulk organic carbon in diverse soil and biochar types on-farm.