In the studies on nutrition of and fertilization for deciduous fruit trees in Japan, the ¹⁵N tracer method has been effectively used in the last 25 years. Through that method, absorption rates of fertilized nitrogen in apple, grape, and peach trees were well identified, ad translocation and distribution of absorbed nitrogen were clearly separated from nitrogen reserved in plants and stored in soils. In the course of long-term cultivation of fruit trees, the applied nitrogen moves around the orchard among soils, grass and trees. In the growth of fruit trees, contributions of soil nitrogen are very large, while in so culture, surface grass plays an important role in controlling nutrient circulation. The results of these analytical studies have been effectively utilized in rationalizing practices of fertilization and soil management in orchards in Japan.