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Comparison of a Forced-draft Technique to Nitrogen-15 Recovery for Measuring Ammonia Volatilization Under Field Conditions¹

ABSTRACT

Reliable field measurements of NH₃ volatilization are necessary for evaluating N-fertilizer efficiency for sod crops and conservation crop production systems. This study was conducted to compare NH₃ loss measurements under field conditions using a forced-draft technique and recovery of urea-¹⁵N. Measurements were made from urea solution applied at a rate of 100 kg N ha^–1 to a bare or mulched Cecil sandy loam soil (Typic Hapludult). In an adjacent area, microplots were established to which urea enriched with ¹⁵N was added. Ammonia losses from the bare and mulched soil were 49 and 72% of the applied N by the forced-draft technique, and 14 and 46% of the applied N by ¹⁵N recovery. The air flow rate with the forced-draft technique was shown to exceed the actual wind speed near the soil surface 10 and 50% of the time for bare and mulched soil, respectively. These results raise serious questions about the validity and accuracy of the forced-draft technique. The usefulness of the forced-draft technique may be limited to relative comparisons of N sources, N rates, and various management practices.

¹ Contribution from the Agron. Dep., Georgia Agric. Exp. Stn., Experiment, GA 30212, and the Agric. Res. Branch, National Fertilizer Development Center, TVA, Muscle Shoals, AL 35662. Supported by Hatch and State funds allocated to the Georgia Agric. Exp. Stn. and by funds allocated to TVA.

² Associate Professor, Agron. Dep., Georgia Station; Research Soil Chemist, NFDC, TVA; Laboratory Assistant and Graduate Research Assistant, Agronomy Dep., Georgia Station, respectively.

Received for publication May 21, 1986.