Fourier-transform infrared (FTIR) analysis was performed to test
the quality of the study biochar. Ground biochar (0.3–0.5 mg) was
embedded in potassium bromide (KBr) pellets (99.5–99.7 mg) and
measured on an FTIR spectrometer (VECTOR 22, Bruker, USA) with
a 4 cm−1 resolution and 100 scans between wavenumbers of 4000
and 400 cm−1 (Chun et al., 2004). To analyze C forms from the FTIR
spectra, we subtracted the background of the KBr window, automatically
corrected the baseline and smoothed the spectra, identified
the peaks, and normalized the spectra on a reduced portion of the
wavenumbers (4000–500 cm−1).