Objectives The study was conducted to quantify the fertilizer nitrogen (N) fates at different winter wheat (Trticum aestivums L.) growth stages (anthesis, grain filling and harvest) and to investigate the effects of differential timing of fertilization on N uptake and translocation in winter wheat.
Methods A pot experiment on winter wheat was employed. Urea labeled with 15N was used as N fertilizer source, and half of the N 90 mg/kg was applied as basal and half as topdressing in the elongation stage. Destructive samplings were undertaken at the stages of anthesis, grain filling and harvest. 15N contents in wheat root, shoot and grain and soil were all determined.
Results Majority (57.2%) of total N uptake by winter wheat was derived from fertilizer N over the entire growing season, of which the contribution of basal and top-dressing fertilizer N was 26.6% and 30.6%, respectively, and the remaining 42.8% was from soil N pool. The uptake of fertilizer 15N via winter wheat increased with the crop development: from the flowering to the harvest the increase was 50%, and during the same period, the residual fertilizer 15N declined by 50%. After the harvest, about 28.6% fertilizer 15N was left in the soil and 33.9% was lost in various pathways. The loss rate of basal fertilizer 15N was 21% higher than that of top-dressing fertilizer 15N. Total recovery of fertilizer 15N via winter wheat was 37.5%, of which the amount in grain was 4 times of that in straw and root. About 64.9% of N in grain was transferred from the vegetative organs developed before the flowering stage.
Conclusions About 60% and 40% of the total N uptake by winter wheat was from fertilizer and soil, respectively. Basal and top-dressing fertilization contributed equally to the wheat N uptake. At current farmer’s fertilization level for winter wheat, i.e., N 250 kg/hm2, an increase of top-dressing N fertilization may decrease the N losses. Residual fertilizer N was significant to compensate the N consumed by winter wheat.
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