A field experiment was conducted to evaluate the fate of nitrogen (N) derived from fertilizer (fertilizer-derived N) applied to a paddy field after rice harvesting to promote rice straw decomposition during the fallow season, and to determine its effect on soil N fertility in northern Japan. A frame containing soil mixed with rice straw and 15 N-labeled fertilizer (4.3 g N m −2 ammonium sulfate [AS] or lime-nitrogen [LN]) was placed into a paddy field on a gray lowland soil during the fallow season (October-April), and the following rice-growing season (May-September). Before cultivation (April), the percentages of fertilizer-derived N in soil + straw were higher for LN (55-72%) than for AS (41-63%). At the harvesting stage (September), the percentages of fertilizer-derived N in plants were significantly higher for LN (4.9-6.2%) than for AS (3.4-5.3%), and the percentages in soil were also significantly higher for LN (42-61%) than for AS (31-38%). This could be attributed to the nitrification inhibitory effect of LN and result in the suppression of N losses via leaching. Consequently, fertilizer-derived N could contribute to the maintenance of soil N fertility, and this effect could be higher for LN than AS.