that had higher d15N values than NO3
, as NO3
concentrations decreased (Table 1), consistent with the
findings of Choi et al. (2002).
For cabbages receiving urea, the d15N of whole plant at
20 DAT (4.1% in the U2 treatment) was significantly
lower than that of urea (0.7%), and this was attributable
to preferred assimilation of 15N-depleted NO3
to NH4
+
(Table 1). At 40 DAT, however, cabbages in the U2
treatment assimilated 15N-enriched NH4
+ and NO3
produced
by nitrification, resulting in a significantly higher
plant d15N at 40 DAT than at 20 DAT (Fig. 1).