Abstract
The efficiency of dividing soil samples into several groups by taxonomical group, soil chemical properties and history of soil management were investigated to estimate more efficiently the amount of available nitrogen released under waterlogged conditions using phosphate-buffered solution. As the indicators of soil chemical properties, C/N ratio, phosphate absorption coefficient, free iron oxide, extractable iron and manganese with pH 3-ammonium acetate, and cation exchange capacity (CEC) were investigated. 1) The relationship between amount of available nitrogen released under waterlogged conditions and amount of extractable nitrogen showed higher correlation when we divided Andosol soil samples into two groups by the phosphate absorption coefficient at 18 g kg^<-1> Wet Andosol soil samples could not be divided clearly. 2) The relationship between amount of available nitrogen released under waterlogged conditions and amount of extractable nitrogen showed higher correlation, when we divided Yellow soil samples into two groups by CEC at 20 cmol(+) kg^<-1> 3) The relationship between amount of available nitrogen released under waterlogged conditions and amount of extractable nitrogen showed higher correlation in Gray Lowland soil samples when we exclude the soil samples below the sum of pH 3-ammonium acetate extractable iron and manganese oxidation-reduction equivalence at 2 mmol kg^<-1> The relationship between amount of available nitrogen released under waterlogged conditions and amount of extractable nitrogen showed higher correlation when we divided Gley soil samples into two groups by the sum of pH 3-ammonium acetate extractable iron and manganese oxidation-reduction equivalence at 4 mmol kg^<-1>.
