In order to improve the management of nitrogen (N) fertilization in pear orchards, we investigated the effects of application timing on the distribution, storage, and remobilization of N in mature pear trees in a field experiment at Jingtai County, Gansu Province, China. Nine trees were selected for the experiment and each received equal aliquots of 83.33 g N in the autumn, spring, and summer, with ¹⁵N-labeled (NH₄)₂SO₄ used in one of the aliquots each season. Results showed that the (¹⁵N H₄)₂SO₄ applied in the autumn remained in the soil during the winter. In the following spring this N was absorbed and rapidly remobilized into each organ, especially new organs (leaves, fruit and new shoots). The ¹⁵N supplied in spring was rapidly transported to developing fruit between the young fruit and fruit enlargement stages. ¹⁵N from the summer application of fertilizer was mainly stored in the coarse roots over the winter, then was mobilized to support growth of new organs in spring. In conclusion, for pear trees we recommend that the autumn application of N-fertilizer be soon after fruit harvest in order to increase N stores in fine roots. Spring application should be between full bloom and the young fruit stages to meet the high N demands of developing fruit. Summer application of fertilizer at the fruit enlargement stage does not contemporaneously affect the growth of pears, but increases the N stored in coarse roots, and in turn the amount available for remobilization in spring.

为了改善梨园氮肥的管理，我们在甘肃省景泰县进行了田间试验，研究了施肥时间对成熟梨树中氮素的分配，储存和迁移的影响。选择9棵树进行实验，在秋季，春季和夏季，每棵均等分83.33 g N，在每个季节中，等分之一使用¹⁵ N标记的（NH ₄）₂ SO ₄。结果表明（¹⁵ N H ₄）₂ SO ₄秋季施用，冬季保留在土壤中。在接下来的春天，氮被吸收并迅速转移到每个器官中，尤其是新器官（叶子，果实和新芽）。春季供应的¹⁵ N在幼果期和果实膨大期之间迅速转运到发育中的果实。¹⁵夏季施用的氮肥主要储存在冬季的粗根中，然后在春季动员以支持新器官的生长。总之，对于梨树，我们建议在果实收获后尽快秋季施用氮肥，以增加细根中的氮含量。春季施肥应在盛花期与幼果期之间进行，以满足对发育果实的高氮需求。夏季在果实膨大阶段施用肥料不会同时影响梨的生长，但会增加储存在粗根中的氮，进而增加春季可动员的氮含量。