**Acknowledgements**

The author is grateful to Mr. Mitsuhiko Nukada, Mr. Yuichi Saito, and Mr. Yuji Ono, Fruit Tree Research Center, Agricultural Technology Center, Fukushima Prefecture, Japan, for their cultivation management of "Jonathan" apple trees in the long-term nitrogen-fertilization experimental field. Parts of the results in this review were obtained from the long-term nitrogen-fertilization experimental field. The continuous research "Long-term changes in yield, fruit quality, mineral contents, and soil chemical properties in the apple "Jonathan" orchard to which ammonium nitrate had been applied for over 40 years" has been conducted in this field, which was supported by Grants for Environmental Research Projects by the Sumitomo Foundation to K. Matsuoka in 2014 (no. 143404).
