Abstract
The cylinder method was used in situ to estimate net mineralization in surface soil (0-10cm depth) of an established (83-year-old) stand and young (2-year-old) stand of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obutusa). The upper and middle part of the established stand and the upper part of the young stand consisted of hinoki and the lower part of the established stand and middle and lower part of the young stand consisted of sugi. Measurement sites were in the upper, middle, and lower sections in both stands. The amounts of inorganic nitrogen (NO_3-N+NH_4-N) found in the soil (0-10cm depth) were 1-10kg・ha^<-1> during one year, and no obvious differences between the sugi and hinoki stands or among the plots. The ratio of NH_4-N to inorganic nitrogen were decreaed from the upper to lower slope position in both the established and young stands. When the average soil temperature for one month became higher than above 5℃, net nitrigen mineralization occured and was accelerated with an increase of soil temperature. Net nitrogen mineralization increased from the upper to lower slope position in both the established and young stands. The ratio of NH_4-N to net nitrogen mineralization was higher in the established stand than in young stand. The ratio increased from the lower to upper slope position in the established stand, but there was no differece among the plots in the young stand. The net nitrogen mineralization in surface soil (0-10cm depth) in the established stand was 45-55kg ha^<-1>・yr.^<-1> and in the young standa was 50-80kg ha^<-1>・yr.^<-1>.
