The conventionally-modified RothC model for Andosols required pyrophosphate-extractable aluminum (Alp) for changing humus decomposition rate of the original RothC model. However, any Japanese soil database, which were derived from national soil survey projects, did not have the Alp dataset, and thus the conventionally-modified RothC model required Alp prediction from soil organic carbon (SOC) content. From this reason, there is a risk of Alp prediction error in the run-up to predict the SOC turnover. Objectives of this study were (1) to explore the alternative soil property for re-modifying the conventionally-modified RothC model and (2) to validate the re-modified model against long-term experimental data sets of Japanese Andosols. Phosphate adsorption coefficient (PAC), which is an indicator of the content of amorphous aluminum (Al) and iron (Fe) compounds, was tested to replace Alp using three Andosols database. A stability factor, H(f), was defined as the factor needed to divide the decomposition rate constant of the humus pool so that the modeled SOC level matched the measured level. Phosphate adsorption coefficient showed positive correlation with the H(f). The H(f) was regressed by the exponential equation using PAC as an independent variable, and its R 2 value was higher than in the Alp derived regression. We incorporated the PAC derived regression into the original RothC model as the PAC-modified RothC model. From the comparison of the models validity, the PAC-modified RothC model showed low mean error with low root mean square error in the long-term experimental data sets. These results indicate that PAC can replace Alp for changing the decomposition rate of humus pool in RothC model with accuracy enhancement.
ASJC Scopus subject areas