Modification of Decomposing Coefficient in Humus Accumulation Model Applied to Tephra-soil Sequence in Japan.

Abstract

The purpose of this study is to modify the decomposition coefficient (r) of the reversing Jenkinson's model: Cmax=C/exp-0.000125 t applied to humus accumulation in tephra-soil sequence. The decomposing coefficient (r) was optimized by the following procedure.1) Examine the inorganic colloid components conducted by selective dissolution analysis to understand the state of humus bonding with aluminum that was considered to assign the age limitation for applying the model. 2) Examine the relationship between present climatic condition represented as Humidmine the direction of modifying the decomposing coefficient (r). 3) Determine the decomposing coefficient (r) by applying the enlarged or reduced coefficient (r) to the reversing Jenkinson's model on the assumption that equilibrium carbon content three representative tephra-soil sequences, Aso, Ashitaka and Towada in Japan. Since chronological sequence of Cmax, the equilibrium carbon content, in the Holocene soils resembled to the other proxy data of past environmental change, it may be considered that the equilibrium value of humus accumulation in the buried soils of tephra-soil sequence reflect the strength of the past solar radiation as the background condition of the yield of plants.