ELEMENTARY COMPOSITION, HUMUS COMPOSITION, AND DECOMPOSITION IN SOIL OF CHARRED GRASSLAND PLANTS

Charred plant residues collected after the burning of grassland vegetation in which Susuki plants predominated (Eulalia, Miscanthus sinensis A.), were divided into 5 particle size fractions of > 2, 1-2, 0.5-1.0, 0.25-0.5, and < 0.25 mm using sieves. 1) The percentage distribution of organic matter in the charred plant residues was higher in the larger particle size fractions, and the reverse was true for the distribution of ash. 2) The contents of carbon, hydrogen, and oxygen of each fraction on an oven-dried basis decreased with decreasing particle size, but the ash content showed an inverse relationship. No regular trend was found between the nitrogen content and the particle size. 3) The atomic H/C and O/C ratios of each fraction and other data suggested that dehydrative condensation took place during the burning of the grassland vegetation studied. 4) The amounts of NaOH-extractable materials from each fraction which were very small significantly increased after the HNO3 treatment of the fractions. The extraction ratio of organic matter, amounts of humic and fulvic acids, and ratio of humic acid in the NaOH-extractable organic matter decreased with decreasing particle size. The humic acids produced belonged to A type, and their absorption curves were similar to those of A type soil humic acids. 5) When several fractions were separately added to a sample of volcanic ash soil and incubated at 25-degrees-C under moist conditions, their fractions were hardly decomposed by microorganisms even after 40 weeks.