Abstract: The relationship between topdressing nitrogen at seedling stage (before three leaves and one heart period) of dry seeded rice followed by winter wheat and yield forming, also the law of requiring nitrogen at seedling stage were probed with 15N traced technique under the conditions of both field and pot cultured during 1985-1986. The results indicated that rice seedling utilized native soil-N much more than fertilizer-N, only about 1/4-1/5 of the nitrogen in seedling came from the fertilizer. Therefore, the dry seeded rice was lower at utilizing nitrogen at seedling stage, it is very important to raise soil fertilizer for rice seedling growing under drying condition. From the economical view, in the fertile soil, it is not suggested to topdress fertilizer at seedling stage of dry seeded rice followed by winter wheat.

Key words: Nitrogen efficiency, Dry seedel rice, Nitrogen application at rice seedling period