Isotopic N-15 tracers have been important tools in the understanding o
f N cycling in agricultural and natural soil-plant systems. The object
ives of this research were to quantify losses of N-15 under controlled
conditions, evaluate (NH3)-N-15 transport between plants, and assess
the potential for error associated with the use of N isotopes, Corn (Z
ea mays L.) was grown hydroponically in 5- to 15-mm-diam. gravel in tw
elve 162-L barrels. All N was applied as NO3 with enrichment periods o
f full season, planting through anthesis, anthesis to harvest, or no N
-15 applied. Plant growth and total N accumulation followed normal gro
wth curves and maximum N content was obtained at synthesis. When N-15
treatments stopped at anthesis, plants lust N-15 (presumably as (NH3)-
N-15) equivalent to about 23% of total plant N between anthesis and ha
rvest. In treatments in which N-15 applications started at anthesis, t
otal N content in the leaves and stems decreased between anthesis and
harvest while N-15 content increased indicating a substitution of rece
ntly absorbed N for N compounds translocated to the fruit. Volatile lo
sses of N indicate that caution must be exercised when conducting and
interpreting N-15 experiments. Significant plant-to-plant transport of
(NH3)-N-15 showed that decreases in plant N-15 content could not be u
sed to estimate NH3 volatilization for an entire field.