Nitrogen mineralization of soil and soil particle fractions with long-term annual combined application of manure and chemical fertilizer in a wheat/rice rotation system was monitored during a 112-day laboratory incubation NH₄⁺ and NO₃^-in leachates were measured after soil samples were incubated for 1,2,4,6,8,10,12,14 and 16 weeks at 25 Nitrogen mineralization potential(N₀)and mineralized rate constant(k)were fitted using a first order equation N₀ value of soil and soil particle fractions was significantly increased after 14-year incorporation of pig manure and straw,however,there was no significant effect on k value The N mineralizability in different soil particle fractions increased in the order:0~2 m>2~10 m>50~100 m>10~50 m A pot experiment was also conducted to determine the basic nitrogen supply of the soil and soil particle fractions during 16-week growth of ryegrass The results showed that the amount of N mineralized during the incubation was greater than those taken up by ryegrass,suggesting that it is worthwhile making some modifications when we make comparison of the results obtained from incubation and pot experiments.