Changes in elementary composition and humus composition in the burning process of susuki (Miscanthus sinensis A.) plants at various temperatures

We investigated the burning process of Susuki plants at various temperatures (150, 200, 250, 300, 350, 400 and 450 degrees C) giving special attention to the elementary composition and humus composition. 1) When the Susuki samples (non-heated samples) were heated at 150 and 200 degrees C, the samples were not burned and changed to brown in color due to heat applied (non-burned samples). At the temperature of 250 degrees C or higher, the samples were burned, and consequently charred residues and ash were produced (burned samples). 2) The ratios of amounts of dry material, carbon, hydrogen and oxygen remaining in the heated samples, as compared to those originally present in the non-heated samples, were much lower in the burned samples than in the non-burned samples. Such a relationship was not found for nitrogen or ash. 3) The results of an elementary analysis indicated that the carbon content (ash-free oven-dried basis) tended to increase with the increase of heating temperature, but the reverse was true for oxygen content. There was no regular relationship between the hydrogen and nitrogen contents and the heating temperature. The atomic [H]/[C] and [O]/[C] ratios in the burned samples were much lower than those in the non-burned and non-heated samples. The burning process of susuki plants was mainly arranged in the direction of dehydration on the [H]/[C] versus [O]/[C] diagram. 4) The results of humus analysis indicated that the extracted humus, humic acid and fulvic acid contents (ash-free oven-dried basis) in the burned samples were much lower than those in the non-burned simples. There was no relationship between the total humus content and heating temperature. 5) The humic acids extracted from the non-heated and non-burned samples were of the Rp type. The humic acids in the burned samples were A type, and the amount of acid decreased with the increase of heating temperature