Abstract
The actual conditions of α-glucosidase activity (α-G) as an index of microbial activity, and also microbial biomass (BM) in the volcanic ash soils distributed in the central part of Hokkaido (Central Hokkaido) were estimated in 1995 and 1996. Then, the relationship between α-G, BM and soil physical properties was discussed. α-G and BM in the volcanic ash soils in the Tokachi district of Hokkaido (Tokachi) were used for comparison. 1) The average values of α-G in Andic Regosols (c-AR) and Humic Andosols (c-HA) in Central Hokkaido in both years ranged from 240 to 280 pmol g^<-1> min^<-1> and from 420 to 470, respectively. They were pretty much lower than those in Ochric Andosols (604) and Humic Andosols (624) in Tokachi in 1995.2) The volume of biomass C (BM-C) in c-AR and c-HA was 35 and 110 mg C kg^<-1>, respectively. These volumes were less than half of the values in the above two soils in Tokachi. BM-C per total C was also less than that in Tokachi, but qCO_2 was contrary. 3) α-G was positively correlated with BM-C, BM-N and CO_2 release from the soil (CO_2-C). The volume of CO_2-C in Central Hokkaido was mostly lower than that in Tokachi. a-G per CO_2-C was also a little lower. Then, factors affecting low α-G in Central Hokkaido would be small amounts of substrate and biomass, and also low relative activity. 4) α-G and BM-C were positively correlated with the liquid phase ratio through the above four soils. They were positively the correlated with the solid phase ratio only in c-AR, whereas they were negatively correlated with the solid phase ratio in the two soils in Tokachi. Also, they were negatively correlated with the air phase ratio in c-AR. α-G and BM-C, through the two soils in Central Hokkaido, were positively correlated with clay content. 5) Soil physical properties in Central Hokkaido are sandy and low water retention. α-G was higher in treatments with perlite or bentonite, which were amended to c-AR, so water retention was also another factor affecting microbial activity.
