Incorporation of N-15-labelled fertilizer nitrogen into upper vegetative plant parts in wheat and its mobilization during grain development

The incorporation of N-15-labelled fertilizer nitrogen into the plant parts of winter wheat (Triticum aestivum L.), most important from the point of view of N-mobilization during grain development, was investigated in this study. The microplot N-fertilization experiments were carried out on an eutric Cambisol of medium N-status in Keszthely (Hungary). In addition to an unlabelled N-dose of 80 kg ha(-1), applied in autumn, spring doses of N-15-labelled N-fertilizer were employed. From a grain moisture content of 70% to full ripening, six harvests were done. The flag-leaf blade, flag-leaf sheath, uppermost internode, glumes, rachis and grains from 100 plants were separated each time. From the 60 kg ha(-1) N-dose applied at shooting (Feekes scale 6), in addition to the 60 kg N ha(-1) given at tillering (Feekes scale 2-3), the amount incorporated into the vegetative plant parts was 45% higher. The extent of the N-incorporation was 2.5-fold higher as a result of doubling of the 60 kg N-dose applied at tillering. The proportion of the N-15-fertilizer nitrogen in the total nitrogen was similar in the different plant parts, but it varied from 12.4 to 30.6% as an effect of different N-fertilizations. N-depletion of different quantity and rate from the tested vegetative plant parts could be detected. The labelled fertilizer-N mobilized from the vegetative parts above the top node accounted for 49-62% of N-15 contained in the ripe grains per ear in the different N-treatments. Irrespective of the different timing or doses of N-applications, the flag-leaf blade and uppermost internode showed the greatest relative N-depletions.