Abstract
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 3 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°C under moist conditions, their fractions were hardly decomposed by microorganisms even after 40 weeks.