Seasonal variations in soil microbial biomass content and soil neutral sugar composition in grassland in the Japanese Temperate Zone

Abstract We investigated seasonal variations in the soil microbial biomass N content (MBN) and the soil neutral sugar composition from April 1995 to September 1996 in cattle-grazed pasture in a Japanese Andisol. MBN showed seasonal variation, gradually increasing from April to August, and decreasing rapidly by the end of August when soil moisture content decreased. Soil inorganic-N increased after fertilization and cattle pasturage. Seasonal variations in seven types of neutral sugar-C contents in the soil were observed. However, the trends in seasonal variation for sugars derived from plant materials were different from one another and from those derived from microbial products. Seasonal variation trends in soil neutral sugar-C were similar to that of MBN, with a sharp decrease in midsummer and a subsequent increase in autumn probably due to dence pasture plant growth. Furthermore, galactose-C (Gal), rhamnose-C (Rham) and ribose-C (Rib) that originated mainly from microbes showed positive correlations with MBN, but the other forms of soil neutral sugar-C did not. It was concluded that the composition of the soil organic matter accumulated in grassland varied seasonally, and that these seasonal variations can be investigated by MBN or by soil neutral sugar composition.