Relationship between aggregate size and organic matter characteristic in Japanese forest soils

Nagano, Hirohiko   ; Koarashi, Jun   ; Atarashi-Andoh, Mariko  

It is important to examine the relationship between the size of soil aggregates and the density and property of soil organic matter associating with aggregates, in order to understand the process of soil carbon stabilization. However, the relationship between aggregate size and soil organic matter characteristics varies depending on soils. Then, it is difficult to estimate the relationship without the aggregate fractionation. In this study, we investigated the relationship between aggregate size and carbon (C) and nitrogen (N) concentrations of aggregates for several soils collected from Japanese forests. In a soil collected from a forest of Miyazaki (phosphoric acid absorption coefficient was 14 g PO/kg), both C and N concentrations were similar among different sizes of aggregates. In a soil from a forest of Hiroshima (phosphoric acid absorption coefficient 4 g PO/kg), C and N concentrations in micro-aggregates were two-hold higher than those in macro-aggregate. Although further evaluation using more forest soils is necessary, the dependence of the organic matter concentration on the aggregate size could be estimated from the phosphoric acid absorption coefficient.