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Apparent Atmospheric Nitrogen Loss from Hydroponically Grown Corn

USDA-ARS, Southern Piedmont Conservation Res. Ctr., 1420 Experiment Station Rd., Watkinsville, GA 30677.

^* Corresponding author (rsharpe{at}uga.cc.uga.edu).

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

Received for publication March 2, 1996.