Biochar application to soil is a strategy to decelerate the increase in the atmospheric carbon concentration. The composition of condensed aromatic clusters appears to be an important determinant of the degradation rate of char in soil. The objective of the present study was to determine the size distribution of carbon layer planes in biochars produced from different types of feedstock (a broadleaf and a coniferous tree and two herbs) using different heating treatment temperatures (HIT; 400 degrees C-800 degrees C) using Xray diffraction 11 band profile analysis. C-13 nuclear magnetic resonance with the phase-adjusted spinning side bands of the chars indicated different spectral features depending on the HIT and similar carbon composition among the plant types at each HIT. Both the content and composition of carbon layer planes in biochar produced using the same HTF were also similar among the plant types. The carbon layer plane size in the 400 degrees C and 600 degrees C chars was distributed from 0.24 to 1.68 or 1.92 nm (corresponding to 37 or 52 rings) with the mean size of 0.79-0.92 and 0.80-1.14 nm, respectively. The carbon layer planes in the 800 degrees C chars ranged from 0.72-0.96 nm (7-14 rings) to 2.64-3.60 nm (91-169 rings) and the mean values were 1.47-1.89 nm. The relative carbon layer plane content in the 600 degrees C and 800 degrees C chars was typically 2 and 3 times that in the 400 degrees C chars. These results indicate the progression of the formation and/or the size development of graphite-like structures, suggesting that a char produced at a higher HIT would have better carbon sequestrating characteristics. (C) 2016 Elsevier Ltd. All rights reserved.