15N trace technique were used to explore the fertilizer nitrogen (N) absorption and utilization, soil residue and soil nitrogen pool budget under different nitrogen fertilization levels (0, 50, 100, 150, 200, 250 kg·hm-2) for five-year-old 'Yanfu 3'/SH6/M. hupehensis Rehd. from germination stage to new shoot growing stage. The results showed that 15N were preferentially distributed to the roots and then transported to aboveground for the construction of new organs after N application in early spring. After the end of new shoot growing (two months later after N application), 5.9%-9.9% of fertilizer N was absorbed by apple tree, 29.8%-33.4% of fertilizer N was resided in 0-60 cm soil, and 56.7%-64.4% of fertilizer N was lost. With the increases of N application rate, the amount of fertilizer N absorbed by trees and the amount of soil residual N gradually increased, the utilization ratio of fertilizer N and soil residual ratio decreased, and the loss and the loss ratio of N were increased. With the increases of N application rates, the total balance of soil N changed from deficit to surplus, and the surplus increasing significantly with the increases of N application rates. The results indicated that low N application rate could cause a decrease of soil N fertility and the excessive application of nitrogen could increase the accumulation of N and increase the risk of N pollution. Fertilizer N levels showed a significant linear correlation with soil total N balance, with the regression equation being y=0.3511x-20.808 (R2=0.9927). In the stages from germination to new shoot growing, soil N pool reached balance when the N application rate was 59.27 kg·hm-2.
运用15N同位素示踪技术,以5年生‘烟富3’/SH6/平邑甜茶苹果为试材,研究了萌芽至新梢旺长期不同施氮水平(0、50、100、150、200、250 kg·hm-2)下肥料氮的吸收利用、土壤残留和土壤氮库盈亏特点.结果表明: 早春施氮后,15N均优先分配到根系中,然后转运用于地上部新生器官(果实、新生枝叶)的形态建造.新梢旺长期结束后(施氮2个月后),5.9%～9.9%的肥料氮被树体吸收,29.8%～33.4%的肥料氮残留在0～60 cm土体中,56.7%～64.4%的肥料氮通过其他途径损失.随施氮水平的提高,树体吸收的肥料氮量和土壤残留氮量逐渐增加,但肥料氮利用率和土壤残留率却不断降低,同时损失量和损失率不断增加.随施氮水平的提高,土壤氮素总平衡由亏缺转为盈余,且盈余量随施氮水平的提高而显著提高.表明施氮不足将会造成土壤氮肥力的下降;而过量施氮则会加剧土壤氮素累积,增加氮素污染风险.施氮水平与土壤氮素总平衡呈显著线性相关关系,拟合方程为:y=0.3511x-20.808 (R2=0.9927),当施氮量为59.27 kg·hm-2时,由萌芽至新梢旺长期的土壤氮库达到平衡.
Keywords: apple tree; germination stage; new shoot growing stage; nitrogen fate; nitrogen level; soil nitrogen budget.