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Title: RELATIONSHIPS AMONG SOIL NITRATE, LEAF NITRATE, AND LEAF YIELD OF BURLEY TOBACCO: IMPACTS OF N MANAGEMENT

Author
item MACKOWN, CHARLES
item CRAFTS-BRANDNER, STEVEN
item SUTTON, TOMMY - UNIV. OF KENTUCKY

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Burley tobacco (Nicotiana tabacum L.) requires large amounts of fertilizer N to produce high yields of cured leaf possessing quality traits demanded by leaf buyers. Effects of N fertilizer on relationships among leaf yield, leaf NO3, and soil NO3 levels were determined. Burley tobacco was grown in 1991 and 1992 at two locations and N was broadcast applied at 0 to 448 kg N/ha before transplanting or banded at 168 kg N/ha about 5 wk after transplanting. Cured leaf yields and lamina NO3 increased with increasing fertilizer N applied. Yield increased 3.7% with banded N as compared to an equivalent amount of broadcast N. Banding N increased the NO3 level of cured leaf lamina 37% for bottom leaves and 17% for middle leaves, while leaves from the top were unaffected. Depending on location, critical soil mineral N values of 46 and 56 mg/kg were estimated from average mineral N concentration in the upper 30 cm of soil sampled at 3 and 5 wk after transplanting. Early-season soil NO3 tests to predict the NO3 level of cured leaf lamina does not appear feasible. At 280 kg N/ha, a commonly recommended N application for burley tobacco, as much as 37 mg NO3-N/kg soil was found in the upper 30 cm of soil following harvest. Decreasing the amount of fertilizer N broadcast just before transplanting to 168 kg N/ha caused a 10% reduction in yield, a 37 to 65% decrease in lamina NO3 and about a 60% decrease in residual soil NO3 at harvest. With better N management decreases in the NO3 level of cured leaves and the amount of residual NO3 following harvest should be possible.

Technical Abstract: Large amounts of fertilizer nitrogen (N) are used to produce substantial yields of high quality burley tobacco. Excessive N use produces air- cured burley leaves with undesirable high levels of nitrate and could be economically unfavorable and environmentally unsound, if substantial levels of soil nitrate remain following harvest. Effects of N fertilizer on relationships among leaf yield, leaf nitrate, and soil nitrate levels were determined. Air-cured leaf yields and lamina nitrate increased with increasing fertilizer N applied. Early-season soil nitrate tests were found to be useful to predict the need for additional sidedress fertilizer N, but were not useful to predict the nitrate concentration of air-cured leaves used by manufactures of tobacco products. Decreasing the amount of fertilizer N broadcast just before transplanting to 150 lb N/acre caused a 10% reduction in yield, a 37 to 65% decrease in lamina nitrate and about a 60% decrease in the amount of soil nitrate at harvest. With better N management decreases in the nitrate concentration of air-cured leaves and the amount of soil nitrate following tobacco harvest should be possible. These results will be useful to agronomist and producers seeking information to increase profits and efficiency of N fertilizer thereby decreasing potential negative impacts of excessive fertilize N use with burley tobacco.