APPARENT ATMOSPHERIC NITROGEN LOSS FROM HYDROPONICALLY GROWN CORN

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.