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Title: EARLY-SEASON PLANT NITRATE TEST FOR LEAF YIELD AND NITRATE CONCENTRATION OF AIR-CURED BURLEY TOBACCO

Author
item Mackown, Charles
item Crafts-Brandner, Steven
item SUTTON, TOMMY - UNIVERSITY OF KENTUCKY

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/1999
Publication Date: 2/15/2000
Citation: Mackown, C.T., Crafts-Brandner, S.J., Sutton, T.G. 2000. Early-season plant nitrate test for leaf yield and nitrate concentration of air-cured burley tobacco. Crop Science. 40(1):165-170.

Interpretive Summary: Good yields of high quality burley tobacco require large amounts of nitrogen (N) fertilizer. Because tobacco is a high value cash crop, producers are likely to over fertilize their crop with N. Excessive use of N fertilizer can be economically unfavorable and environmentally unsound. Also, it can cause burley tobacco leaves to contain high amounts of N in the form of nitrate. High amounts of nitrate in tobacco leaves can pose health concerns and are undesirable for the manufacture of tobacco products. We investigated the effects of N fertilizer on relationships among leaf yield, leaf nitrate content, and nitrate content of young tobacco plants. Knowledge of nitrate content in plants during the first 3 to 5 weeks after planting seedlings was found to offer much promise as a diagnostic test to determine if the N needs of the crop would be met at harvest. It was also a good predictor of the amount of nitrate in the leaf fwhen used by manufactures of tobacco products. For the early-season test to be effective, farmers need to include in each tobacco field to be tested a comparison strip of fertilizer N applied at a rate that produces maximum yield. These results will be useful to agronomist, crop consultants, and producers seeking to increase profits and make better use of their N fertilizer, thereby decreasing potential negative impacts of excessive fertilize N use.

Technical Abstract: Profitable yield and satisfactory leaf quality of burley tobacco (Nicotiana tabacum L.) require proper management of N fertilizer. The level of tissue nitrate in tobacco may be a suitable diagnostic test of crop N sufficiency that could be used for N management decisions. This study determined the suitability of early-season tissue nitrate as a predictor of air-cured leaf fyield and nitrate concentration. Burley tobacco was grown in 1991 and 1992 on a well-drained and moderately well-drained silt loam and broadcast fertilized just before transplanting with 0 to 392 kg N/ha. Nitrate levels of plants sampled from 3 to 5 weeks after transplanting and air-cured leaf yields increased with increasing amounts of fertilizer N. Responses differed depending on location and year. When the results were expressed as % of maximum within year and location, a single linear equation described the relationship of leaf yield to early-season nitrate. However, to use this equation, it would be necessary to include in each tobacco field evaluated a strip of fertilizer N producing near maximum yield. The nitrate concentration of burley tobacco between 3 and 5 weeks after transplanting was suitable for predicting the nitrate concentration of air-cured leaf lamina from the top, middle, and bottom stalk positions, and appeared to be insensitive to year and location effects. Use of plant nitrate concentration, as an early-season diagnostic test to predict N sufficiency and nitrate concentration of cured leaf lamina, appeared to offer much promise for better N management of burley tobacco. However, further research would be needed to calibrate the amount of additional N required to correct N deficits by banding N.