Abstract
We investigated the changes in microbial biomass C and N, available soil N, hot-water extractable C and neutral sugar composition induced by the application of rice straw compost and fertilizer for 29 years to alluvial upland soil in Saitama Prefecture. 1) Long-term application of rice straw compost increased total C and N, microbial biomass C and N, available soil N and hot-water extractable C. Particularly, remarkable increases of microbial biomass N and its ratio in total N were observed in non-mineral fertilizer N application plots where soil pH was high. In addition, there was a negative correlation between soil mineral N content and microbial biomass N. 2) There was a positive correlation between hot-water extractable C content and available soil N content. Except for non-lime plots, the increase in correlation coefficient was much higher. 3) Long-term application of rice straw compost increased the amount of neutral sugar C, particularly xylose C, which is believed to originate from plant material. The ratio of xylose/mannose was higher in rice straw compost application plots than in no-application plots, and lower in no-fertilizer and no-nitrogen plots in both rice straw compost application and no-application plots as compared to other treatment plots. 4) The amount of neutral sugar C was correlated positively with that of available soil N. Particularly, the amount of xylose C showed the highest correlation coefficient with available soil N. Thus, humus components derived from plant material in soil are important as substrates of soil microbial biomass contributing to the production process of available soil N.
