Relationship between the Size of Microbial Biomass Carbon and the Amounts of Mineral Ions in Arable and Forest Soils

Abstract

We determined the size of microbial biomass-C and the amount of several mineral ions in samples of an arable soil from a field in the campus of Tokyo University of Agriculture & Technology in Fuchu, Tokyo, a secondary forest soil at Sengen-yama in Fuchu and a virgin forest soil at Ogawa in Kita-ibaraki, Ibaraki. Mean microbial biomass-C was 160μg/g dry soil at a depth of 5-10 cm (100 kg/ha at a depth of 0-40 cm) in the arable soil, 560μg/g dry soil (1200 kg/ha) in the secondary forest soil and 1100μg/g dry soil (1500 kg/ha) in the virgin forest soil. Mean amounts of several mineral ions in the soil solution of the arable soil were higher than those of the secondary and virgin forest soils. For example, mean amount of nitrate-N was 4.4μg/g dry soil at a depth of 5-10 cm (17 kg/ha at a depth of 0-40 cm) in the arable soil, 0.01μg/dry soil (0.01 kg/ha) in the secondary forest soil and 0.78μg/g dry soil (0.1 kg/ha) in the virgin forest soil. To prevent nitrate-N leaching from soil into the groundwater, a soil column with arable soil supplied with 104μg NO_3^--N/g dry soil was incubated with or without glucose (2060μg C/g dry soil). The amount of nitrate leaching in the incubated soil with glucose was one fifth of that in the soil without glucose, accompanied by a 3 fold increase in microbial biomass-C.