Fate of fertilizer nitrogen and soil nitrogen pool budget of Fuji apple from germination stage to new shoot growing stage

Abstract

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.