In addition, the magnitude of variations in plant-d15N
after additional N application was greater in C2/U1 plants
than in U1/C2 plants, because urea-N was more available
to plants than compost-N, as indicated by plant N uptake
(Table 2), and this was similar to the results of Choi et al.
(2002) in that the magnitude of decrease in d15N due to
urea application was greater than that of the increase in
d15N due to compost application. Therefore, this result
shows that plant d15N reflects the effect of original isotopic
composition of N inputs as long as isotopically similar N is