Changes in the humus composition of volcanic ash soils by heating at various temperatures

Abstract
Volcanic ash soils in Japan are characterized by the accumulation of large amounts of black humus, and the black color is due to the presence of A type humic acids with a high degree of humification (Kumada 1987). Although there is still no systematic understanding of humus formation in volcanic ash soils, Shindo et al. (1986a, b, c) and Shindo (1991) suggested that charred grassland plants were one of the possible sources of A type humic acids based on several findings.