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

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 va riation, 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 produ cts. Seasonal variation trends in soil neutral sugar-C were similar to that of MEN, with a sharp decrease in midsummer and a subsequent increase in au tumn probably due to dence pasture plant growth. Furthermore, galactose-C ( Gal), rhamnose-C (Rham) and ribose-C (Rib) that originated mainly from micr obes showed positive correlations with MEN, but the other forms of soil neu tral sugar-C did not. It was concluded that the composition of the soil org anic matter accumulated in grassland varied seasonally, and that these seas onal variations can be investigated by MBN or by soil neutral sugar composi tion. (C) 1999 Elsevier Science B.V.