New definition of the qualifiers for Dystric and Eutric should be noted for the classification of Andosols with WRB2014
2020
Kubotera, Hideo | Yamaguchi, Noriko | Kusaba, Takashi
The WRB (World Reference Base for Soil Resources) 2014 adopted ‘effective base saturation (EBS),’ which is the ratio of exchangeable bases (Ca + Mg + K + Na) to effective CEC (Ca + Mg + K + Na + Al), instead of base saturation (BS), the ratio of exchangeable bases to the cation exchange capacity, as the criterion for the addition of qualifiers concerning the condition of exchangeable bases. An EBS of less than 50% was defined as Dystric conditions, and that of 50% or more was defined as Eutric conditions. These newly defined qualifiers were applied to 49 soil samples from grasslands of Andosols in central Kyushu and 132 horizons from a database of Japanese Andosols. It was found that 80% of the samples met the criterion for Eutric conditions according to WRB2014, despite their small amount of exchangeable bases and low BS, whereas only 2% were Eutric when the criterion of WRB2006 (BS ≥ 50%) was used. In the case of uncultivated soils, the definitions of Dystric and Eutric according to WRB2014 corresponded mainly to non-allophanic and allophanic soils, respectively. All pedons of allophanic Andosols were classified as Eutric, but those of non-allophanic Andosols were classified as Dystric, according to WRB2014, because of the high EBS recorded in them. Conversely, all pedons were classified as Dystric based on the WRB2006 criteria. These characteristics of the Dystric and Eutric qualifiers in the classification of Andosols according to WRB2014, which is related to the variable charge of the samples, should be noted for the proper understanding and management of base conditions of Andosols.
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