不同时期追施氮肥对成熟期蜜柚树体氮素分配的影响

Effects of nitrogen topdressing at different stages on nitrogen distribution in mature pomelo trees

【目的】研究不同时期追施氮肥对成熟期蜜柚树体氮素分配的影响,为蜜柚果园氮肥的合理运筹和高效利用提供理论依据。【方法】以7年生红肉蜜柚[Citrus grandis(L.)Osbeck.cv.Hongroumiyou]为试材进行高量(对照)和减量施肥试验。供试尿素以5∶3∶2的比例分别在春梢萌发期、稳果期和果实膨大期追施,在每个时期的追施尿素中加入5%的^(15)N-尿素。在成熟期,采集蜜柚各部位器官样品,测定生物量、氮浓度、^(15)N丰度,计算不同器官从肥料中吸收分配到的^(15)N量对该器官全氮量的贡献率(Ndff)、^(15)N分配率以及^(15)N利用率。【结果】对照处理中,在春梢萌发期追施^(15)N-尿素的蜜柚果实、当年生挂果枝上的叶和枝的Ndff值较高;在稳果期追施^(15)N-尿素的蜜柚果实的Ndff值显著高于其它器官;在果实膨大期追施^(15)N-尿素的蜜柚,则以当年生未挂果枝和叶的Ndff值最高。减量施肥处理中,在春梢萌发期和稳果期追施^(15)N-尿素的,Ndff值在果实、营养器官和贮藏器官与对照相似;在果实膨大期追施^(15)N-尿素的,枝条中的Ndff值都高于叶片,这与对照处理当年生未挂果枝叶Ndff值最高有所差异。成熟期不同器官的^(15)N分配率表现为:对照处理中,在春梢萌发期追施^(15)N-尿素的,果实^(15)N分配率(52.5%)显著高于营养器官(25.5%)和贮藏器官(22.1%);在稳果期追施^(15)N-尿素的,^(15)N分配率以果实中最高(61.3%),其次是贮藏器官(25.4%),显著高于营养器官(13.3%);在果实膨大期追施^(15)N-尿素的,^(15)N分配率在贮藏器官进一步增加至最高(44.0%),其次为营养器官(35.8%),最低为果实(20.3%)。减量施肥中,在春梢萌发期和稳果期追施^(15)N-尿素的,^(15)N在不同器官的分配率与对照相似,而在果实膨大期追施^(15)N-尿素,^(15)N分配率以贮藏器官最大(45.8%),其次为果实(34.3%),最低为营养器官(19.9%)。对照和减量施肥两个处理的氮肥利用率均以春梢萌发期施入^(15)N-尿素的处理最低。对照处理中,^(15)N利用率总体随^(15)N-尿素施用时期的后移而逐步提高,减量施肥中,以稳果期施入^(15)N-尿素处理的利用率最高(37.5%),且减量施肥蜜柚树体各器官的^(15)N利用率均高于对照,并以果实中^(15)N利用率的增幅最大。【结论】利用^(15)N示踪技术研究发现,春梢萌发期施入的氮肥,主要分配到果实以及当年生枝叶中,稳果期施入的氮肥较多分配在果实中,而果实膨大期施入的氮肥可以显著提高贮藏器官的氮素积累,有利于来年果实的生长。因此,在蜜柚生产上,春梢萌发期施肥量可以适当减少,以避免氮肥的大量损失;稳果期施肥作为果实氮素积累的关键施肥时期,施肥量需得到保障;同时需要追施果实膨大肥增加贮藏营养,用于果树的花芽分化,提高翌年果实的产量与品质。适当优化氮肥用量有利于抑制蜜柚果树的过度营养生长,提高果实的氮素利用率,具体优化比例还需进一步研究。

【Objectives】The present study investigated the nitrogen demand in honey pomelo tree at different fertilizer application stages under different fertilizer treatments,and provided the theoretical basis for rational management and efficient utilization of nitrogen fertilizer in pomelo orchard.【Methods】Seven-year-old red flesh honey pomelo trees were selected,two kinds of fertilizer application methods were adopted,high fertilizer input was referred to CK and reducing the fertilizer input was refered to fertilizer reduction treatment.The urea amount was divided in ratio of 5∶3∶2,and applied at spring shoot germination stage,fruit stabilization stage and fruit expansion stage,respectively.And 5%^(15)N-urea was added in urea at each stage.In the mature stage,samples of organs from various parts of pomelo tree were taken to measure biomass,N concentration and^(15)N abundance,and calculate the contribution of N derived from fertilizer(Ndff)to the total N contents in different organs,^(15)N distribution,and utilization rate.【Results】In CK,the Ndff of fruit,new shoot leaf with fruit,and new shoot with fruit were higher when^(15)N-urea was applied at the spring shoot germination stage.The Ndff of fruit was significantly higher than other organs when^(15)N-urea was applied at the fruit stabilizing stage.The Ndff of the new shoot and new shoot leaf without fruit was the highest when^(15)N-urea was applied at the fruit expanding stage.In fertilizer reduction treatment,the Ndff of fruit,vegetative organs and storage organs were similar to CK when the^(15)N-urea was applied at the spring shoot germination stage and the fruit stabilizing stage.The Ndff of shoot and branch was higher than leaf when^(15)N-urea was applied at the fruit expanding stage,which was different from CK.The results of^(15)N distribution rate of different organs at the maturity stage were as follows.In CK,the^(15)N distribution rate of fruit was highest(52.5%),followed by vegetative organs(25.5%)and storage organs(22.1%)when^(15)N-urea was applied at the spring shoot germination stage.When the^(15)N application at the fruit stabilizing stage,the fruit still showed the highest^(15)N distribution rate(61.3%),but the^(15)N distribution rate of storage organs(25.4%)was significantly higher than the vegetative organs(13.3%).The^(15)N-urea application at the fruit expanding stage further increased the^(15)N distribution rate of storage organs to the maximum(44.0%),followed by the vegetative organs(35.8%).The^(15)N distribution rate in fruit was the lowest(20.3%).In fertilizer reduction treatment,the^(15)N utilization of different organs were similar to CK when the^(15)N-urea was applied at the spring shoot germination stage and the fruit stabilizing stage.When^(15)N-urea was applied at the fruit expanding stage,the^(15)N distribution rate of storage organs was highest(45.8%),while the^(15)N distribution rate of fruit(34.3%)was higher than that of vegetative organs(19.9%).The^(15)N utilization rate was the lowest in both treatments when^(15)N-urea was applied at the spring shoot germination stage.In CK,the^(15)N utilization rate was gradually increased with the delay of the^(15)N-urea application stage.In fertilizer reduction treatment,the^(15)N utilization rate was the highest(37.5%)when^(15)N-urea was applied at the fruit stabilizing stage.These results showed that the^(15)N utilization rate was higher for the pomelo tree’s different organs under the fertilizer reduction treatment than CK,and the maximum increase rate of^(15)N utilization was in fruit.【Conclusions】By using^(15)N trace technique,it was showed that N was mainly distributed to fruit,new shoot leaf and new shoot when fertilizer was applied at the spring shoot germination stage.Nitrogen was mainly distributed to fruit when fertilizer was applied at the fruit stabilizing stage.Nitrogen fertilizer applied at the fruit expanding stage could significantly improve nitrogen accumulation in the storage organs,which was useful to the fruit growth in the next year.Therefore,in the pomelo production,the fertilizer application at the spring shoot germination stage can be reduced to avoid the loss of nitrogen fertilizer.Fertilizer application at the fruit stabilizing stage is critical for fruit nitrogen accumulation.Nitrogen fertilizer at fruit expanding stage is highly recommended to increase nitrogen nutrition storage,which is used for the flower bud differentiation of the next year and improvement of the yield and fruit quality.Appropriate optimization of nitrogen fertilizer dosage is conducive to suppressing the excessive nutrient growth of pomelo trees and improving the nitrogen utilization rate of fruit.The specific optimization ratio still needs further researches.