Microbial Biomass and Activities along an Andosol Profile in Relation to soil Organic Matter Level

Abstract

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 100 cm deep Andosol profile in an arable field in Matsudo city, central Japan. In the three phase distributions of soil, the solid phase was: 5-10 cm = 15-20 cm>55-60 cm > 35-40 cm = 75-80 cm. Total organic C and N were highest at 15-20 cm (40.4 and 2.8 mg kg-1, respectively) and decreased with depth, being lowest at 75-80 cm (18.6 and 0.6 mg kg-1, respectively). Available P and ammonium N followed the same trend as total organic C and N. However, nitrate N was highest at 35-40 cm (51.6 mg kg-1 soil) and lowest at 5-10 cm (19.1 mg kg-1 soil). Microbial biomass C and N were highest at 15-20 cm (202 and 26 mg 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 75-80 cm. Dehydrogenase activity was highest at 15-20 cm and much lower below this depth (51.2 and 3.3-3.7 μg Triphenyl formazan g-1 soil 24 hr-1, respectively) and was highly correlated with soil microbial biomass (r2 = 0.922, P<0.05). Nitrifying activity was also highest at 15-20 cm and decreased with depth to a low at 75-80 cm. 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. © 2000, Japanese Society of Microbial Ecology – The Japanese Society of Soil Microbiology. All rights reserved.