抄録
Microbial biomass C and N, dehydrogenase and nitrifying activities were measured together with other physicochemical parameters of soil such as the three phase distributions, and the amounts of soil organic matter, mineralizable carbon and nitrogen, in a 100cm deep Andosol profile in an arable field in Matsudo city, central Japan.In the three phase distributions of soil, the solid phase was:5-10cm=15-20cm>55-60cm>35-40cm=75-80cm.Total organic C and N were highest at 15-20cm(40.4 and 2.8mg kg-1, respectively) and decreased with depth, being lowest at 75-80cm(18.6 and 0.6mg kg-1, respectively).Available P and ammonium N followed the same trend as total organic C and N.However, nitrate N was highest at 35-40cm(51.6mg kg-1 soil)and lowest at 5-10cm(19.1mg kg-1 soil).Microbial biomass C and N were highest at 15-20cm(202 and 26mg kg-1 soil, respectively), and showed a tendency to decrease with depth.Mineralizable C and N followed the same trend as microbial biomass C and N and were found to have the lowest values at 75-80cm.Dehydrogenase activity was highest at 15-20cm and much lower below this depth(51.2 and 3.3-3.7μg Triphenyl formazan g-1 soil 24hr-1, respectively) and was highly correlated with soil microbial biomass(r2=0.922, P<0.05).Nitrifying activity was also highest at 15-20cm and decreased with depth to a low at 75-80cm.These properties are important to understanding N dynamics in an Andosol profile, especially the mechanism of nitrate leaching from an arable field to ground water.
