Abstract
Soils applied with different rates of farmyard manure (FYM) or compost were fractionated according to the particle size and the amounts of total C and N, mineralized N during 4 weeks of incubation at 30℃ and muramic acid were analyzed in each fraction. The soils used were sampled from three experimental fields in Japan : Togo (Red-Yellow soil ), applied with FYM at the rate of 0 to 20t/10 a for 8 years ; Kuriyagawa (Ando soil), applied with FYM at the rate of 0 to 32t/10 a for 10 years ; Fujisaka (Ando soil), applied with compost at the rate of 0 to 3.4t/10 a for 43 years. The long-term application of FYM or compost increased the total carbon and nitrogen contents of each particle size fraction, and the relative increase in the amount of organic matter was largest in coarse sand size fraction (>210 μm). The increase in organic matter in coarse sand size fraction due to the organic matter application was remarkable in the soils that received a large amount of FYM, i. e., from Togo and Kuriyagawa. The application of organic matter also increased the amount of mineralizable organic N in each fraction, and the percentage mineralization of organic N was the largest in coarse sand size and clay size (<2 μm) fractions of the soils applied with organic matter. From the distribution of mineralizable N among the particle size fractions, the most important fraction contributing to the N mineralization was the coarse sand size fraction for the Red-Yellow soil whereas the clay size fraction for the Ando soil. The concentration of muramic acid in particle size fractions increased with the increase of the amount of applied organic matter except for the coarse sand size and fine sand size (20-210 μm) fractions of soils from Fujisaka. Significant correlations between the concentrations of muramic acid and the amounts of mineralized N in individual fractions were observed with exception of the fine sand size fraction of the Ando soils. This finding suggested that the microbial cell wall materials were serving as a source of readily mineralizable N in soils applied with organic matter.
