RECOVERY OF FERTILIZER N APPLIED TO BURLEY TOBACCO.

Authors: Mackown, Charles; SUTTON, TOMMY - UNIVERSITY OF KENTUCKY

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fate of fertilizer nitrogen (N) in response to amount and method of N applied was determined for burley tobacco grown in two locations. To evaluate best management practices for N, the fertilizer N use efficiency, amount of fertilizer N accumulated in aboveground plant tissue, and recovery of residual fertilizer N in a winter cover crop were measured using N stable isotope tagged fertilizer. Leaf yield increased with increasing amount of fertilizer N. At equivalent amounts of N, yields for sidedress N treatment were equivalent or slightly less than broadcast applications. The amount of fertilizer N accumulated expressed as a percentage of that applied was a constant 37% for pretransplant broadcast applications of 75 to 300 lb N/acre. Fertilizer N use efficiency increased to about 49% when 150 lb N/acre was sidedress applied just before the onset of rapid growth of the crop at 5 weeks after transplanting. Only 2 to 7% of the broadcast applied N was recovered in a winter cover crop of wheat. Amounts of unaccounted fertilizer could be significantly reduced if fertilizer applications were reduced to give a 10% decrease in leaf yield. However, it is unlikely that producers will accept the use of less broadcast applied fertilizer N and the costs associated with the increased amount of tobacco that would have to be planted to offset the lost value per acre. Drill banding the applied N fertilizer appears to be a viable method to increase fertilizer N use efficiency and lessen the amount of unaccounted fertilizer N without adversely affecting yield and quality of burley tobacco. The results will be useful to agronomist and producers seeking information on increasing N use efficiency and decreasing potential negative impacts of excessive fertilize N use with burley tobacco.

Technical Abstract: Impacts of N management on fertilizer N use efficiency of burley 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 broadcast before transplanting or 168 kg N/ha sidedressed at onset of rapid growth (5 weeks after transplanting). Recoveries of 15N-depleted fertilizer N were determined in aboveground tissues of the tobacco crop. Amounts of fertilizer N recovered at harvest (29-124 kg N/ha) increased with increasing amounts of fertilizer N applied, but fertilizer N use efficiency was constant at 36.6 ñ 0.9% for broadcast applications of N. Sidedress N enhanced fertilizer N recovery (depending on location, 43-54% of applied N) even though total aboveground dry matter was equal to or 12% less than that of plants grown with the same amount of broadcast N. Residual 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 weeks after transplanting. At 13 weeks after transplanting, the difference method, particularly for applications of 84 and 168 kg N/ha, overestimated fertilizer N recoveries when compared to the 15N method, and are 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 decrease air-cured leaf yield by 10% would decrease the unaccounted fertilizer N by 80 to 115 kg N/ha depending on location. As compared to broadcast application of fertilizer N before transplanting, drill banding the N at about 5 weeks after transplanting would equal or further decrease unaccounted amounts of fertilizer N.