ANALYSIS OF PROTON GENERATION AND CONSUMPTION OF FOREST SURFACE SOILS IN HOKKAIDO, NORTHERN JAPAN

摘要

We determined proton budgets of surface soils in a deciduous forest (Df) and a coniferous forest (Cf) of Volcanogenous Regosols in Tomakomai, Hokkaido of northern Japan. The total IT source was 12.9 and 11.6 kmol_c ha~(-1) y~(-1) at Df and Cf respectively, and the external H~+ was 1 % at Df and 2% at Cf. The primary H~+ sources were vegetation uptake of base cations and nitrification, while the major H~+ sinks were release of base cations and NO_3 uptake by vegetation. Leaching incubation experiments using A horizon soils including Df and Cf with NH_4~+ solutions (5.3, 15.9 mg N L~(-1)) showed that H~+ from nitrification was generally higher in the Df soil than Cf soil, and nitrification of Tomakomai Df soil was the highest in both treatments. Results of multiple regression analyses suggested that pH_(ka) and exchangeable Ca~(2+) contributed to the H~+ generation via nitrification. Leaching experiments with dilute HC1 (pH 3.3) revealed that cation release (mainly Ca~(2+)) occurred, and the proportion of release by decrease of exchangeable cations was higher than that by mineral weathering. Mineral weathering in the Tomakomai soil was higher than the other soils.