3.3. Variations in plant-d15N with N sources
The d15N of whole plants varied depending mainly on
the isotopic composition of N sources (compost-, urea-,
and soil-N) (Fig. 1). Cabbages received compost (C4 and
C2) had significantly higher d15N values (Po0:05) than
those received other N treatments, reflecting the higher
d15N value of compost-N than the other N sources (soiland
urea-N). Particularly, the d15N of C4 plants was higher
than that of C2 plants, reflecting the proportionally greater
contribution of compost-N to total plant-N in the C4
treatment (Sikora and Enkiri, 2001). In contrast, the d15N
of cabbages received urea (U2 and U1) was as low as that
of urea, since inorganic-N derived from urea was so
abundant in the soil that cabbage would assimilate urea-N
predominantly over soil-N (Table 1).