Comparison of a Forced-draft Technique to Nitrogen-15 Recovery for Measuring Ammonia Volatilization Under Field Conditions
1987
Hargrove, W. L. | Bock, B. R. | Raunikar, R. A. | Urban, W. J.
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.
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