摘要： 以三年生鸭梨树为试材，应用¹⁵N标记尿素，探讨了不同施氮期土壤中速效氮和肥料氮的动态变化及其与氮素营养的关系。结果表明，不同施肥时期对土壤中NH₄⁺-N影响较小，对NO₃^--N影响较大；不施肥和秋施的土壤中NO₃^--N在年周期内有两个高峰；而春施、夏施仅出现一个峰值。NO₃^--N高峰出现的时间，秋施和春施比不施肥的提前1~2个月，其峰值高3.6~4.4倍。峰值的大小顺序是秋施>春施>夏施；结果还表明，土壤中肥料氮主要分布在0~50cm土层；植株体内总氮量与根层土壤中NO₃^--N含量密切相关。

关键词: ¹⁵N示踪, 鸭梨, 施肥期, 树体营养, 氮素, 动态变化

Abstract: The dynamic changes of the quick-acting nitrogen and the fertilizer nitrogen and their relationship with nitrogen nutrition of Yali-pear tree at different application times were studied, taking the three-year-olds Yali-pear tree as materials and labelling them with 16N.The results showed that the influence of the application time on NH4+-N content in the soil was less and the influence on NO3--N content was greater.There were two NO3--N peaks of the nonapplication and autumn application treatments, but there was only one peak of spring and summer application treatments.The NO3--N peaks of the autumn and spring treatments appeared one to two months earlier compared with the control, and their peaks were 3.6 to 4.4 times higher than that of the control.The height of the NO3--N peaks were ranged in following order: autumn application>spring application >summur application.The results also indicated that the fertilizer nitrogen was disrtributed within 0-50cm soil layer, and the total nitrogen in the tree was highly related with NO3--N content in the root system soil layer.

Key words: ¹⁵N tracing, Yali-pear tree, Fertilizer application time, Nitrogen, Nutrition of Vali-pear tree, Dynamic change