关键词: 苹果, 果实膨大期, 氮水平, 氮去向, 土壤氮素平衡

Abstract: The effect of fertilizer N absorption and utilization，soil N residue and total balance of soil N under different nitrogen levels（0，50，100，150，200，250 kg ? hm-2）were studied using 15N isotope tracer technique during Fuji apple fruit rapid-swelling stage. The results showed that when the nitrogen level was lower than 100 kg ? hm-2，the fruit quality and yield increased significantly with the increase of nitrogen level. But when the level of nitrogen application was higher than 100 kg ? hm-2，there was no significant difference among treatments. With the increase of nitrogen application，nitrogen fertilizer utilization rate decreased gradually. The tree nitrogen from soil nitrogen proportion gradually decreased，and the proportion from fertilizer nitrogen increased；At the end of fruit rapid-swelling stage（after 2 months of nitrogen application），5.98%–13.78% of fertilizer N was absorbed by tree，27.26%–37.38% of fertilizer N was resided in 0–60 cm soil，and 48.84%–66.76% of fertilizer N was lost by other means. With the increase of nitrogen application rate，the amount of fertilizer N absorbed by trees and soil N residue were increased gradually，but the utilization rate of fertilizer N and soil residual rate were decreased，and meantime，the loss and the loss rate were increased gradually. With the increase of nitrogen application，0–60 cm soil inorganic nitrogen（NO3--N + NH4+-N） content increased significantly，and residual inorganic nitrogen in the soil profile is mainly distributed in the topsoil（0–20 cm）. The accumulation of inorganic nitrogen was negative accumulation with no nitrogen and low nitrogen level（50 kg ? hm-2）. When the nitrogen application rate was higher than 100 kg ? hm-2，the accumulation of inorganic nitrogen was positive. With the increase of nitrogen application，soil total nitrogen balance is changed from deficit to surplus，the results showed that low nitrogen application rate could cause the decrease of soil N fertility，and the excessive application of nitrogen could increase the accumulation of nitrogen and increase the risk of nitrogen pollution. The results showed that there was a significant positive correlation between soil total nitrogen balance and nitrogen application rate in the test fertilization level，the regression equation is y = 0.2912x–22.481（R2 = 0.986），soil nitrogen reached balance when the nitrogen rate was 77.20 kg ? hm-2.

Key words: apple, fruit rapid-swelling stage, N level, N fate, balance of soil N