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Recovery of Fertilizer Nitrogen Applied to Burley Tobacco

Charles T. MacKown, Tommy G. Sutton
Agronomy journal 1997 v.89 no.2 pp. 183-189
Nicotiana tabacum, nitrogen fertilizers, measurement, isotope labeling, residual effects, drilling, cover crops, Triticum aestivum, Festuca arundinacea, nutrient uptake, crop yield, application rate, application timing, Kentucky
The high cash value of burley tobacco (Nicotiana tabacum L.) may lead to ineffective excess fertilization Of the crop. The effects of N management on fertilizer N use efficiency by hurley tobacco and recovery of residual fertilizer N by a winter cover crop were determined. Tobacco was grown in 1993 at two locations with 0 to 336 kg N ha⁻¹ broadcast applied before transplanting or 168 kg N ha⁻¹ sidedressed at onset of rapid growth (≈ 5 wk after transplanting). Seasonal recoveries of ¹⁵SN-depleted fertilizer N were determined in aboveground tissues of the tobacco crop. The amount of labeled fertilizer N recovered at harvest (29 to 124 kg N ha⁻¹) increased with increasing amounts of N applied, but fertilizer N use efficiency was constant at 36.6 ± 0.9% for broadcast applications. Sidedress N enhanced labeled fertilizer N recovery (43 to 54% of applied N, depending on location), even though total aboveground dry matter was equal to or 12% less than that of plants grown with the same amount of N applied by broadcast. Recovery of residual labeled fertilizer N in the cover crop ranged from 2 to 7% of applied N and was greatest for the highest amount of N applied. Fertilizer N recoveries estimated by the difference method equaled those of the ¹⁵N method at 5 wk after transplanting. At 13 wk after transplanting, the difference method, particularly for applications of 84 and 168 kg N ha⁻¹, overestimated fertilizer N recoveries relative to the ¹⁵N method, and is unlikely to provide an accurate measure of fertilizer N use by burley tobacco across a wide range of N applications. Reducing the amount of broadcast applied fertilizer to give a 10% decrease in air-cured leaf yield would decrease the unaccounted fertilizer N by 80 to 115 kg N ha⁻¹, depending on location. As compared with broadcast application of fertilizer N before transplanting, drill banding the N at about 5 wk after transplanting would equal or further decrease unaccounted amounts of fertilizer N. Joint contribution of the USDA-ARS and Kentucky Agric. Exp. Stn. Journal no. 96-06-079