Masters Theses

Date of Award

5-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant Sciences

Major Professor

H.P. Denton

Abstract

Burley tobacco (Nicotiana tabacum L.) has historically been fertilized with high nitrogen rates. This study was conducted to evaluate the effect of nitrogen rate on yield and total tobacco specific nitrosamine (TSNA) concentration. The experiment also evaluated the use of in season nitrogen monitoring techniques and how well they were able to predict yield and total TSNA concentration. In 2007, five preplant nitrogen treatments along with two sidedress nitrogen treatments were used. These included: 0, 67, 135, 202, 270 kg/ha nitrogen preplant and 0 and 67 kg/ha nitrogen sidedress. In 2008, there were only four preplant nitrogen rates with the two sidedress nitrogen rates. The 270 kg N/ha was removed for 2008. Also in 2008, four varieties were used and they were KT 204LC, TN 90LC, TN 90HC, and NC 7. Sidedress treatments were applied at three weeks after transplanting. The in season nitrogen monitoringtechniques were the pre-sidedress nitrate test (PSNT), the Cardy nitrate meter, and the CM 1000 chlorophyll meter. PSNT samples were taken before sidedress treatments were applied. Chlorophyll and Cardy meter samples were taken at sidedress, topping, and harvest in 2007. A five weeks after transplant sampling date was added in 2008. Yields were optimized at 135 kg/ha total nitrogen rates. A quadratic plateau model was used to determined critical levels for PSNT and total nitrogen predicting yield and total TSNA. Relative yield plateaued at 0.953 with 204.8 kg/ha total nitrogen applied. A critical PSNT level of 46.4 ppm soil nitrate was established for burley tobacco. TSNA levels increased up to 135 kg N/ha and reached a plateau at 257.8 kg/ha total nitrogen. Total nitrogen applied was the best yield predictor out of the methods used to evaluate nitrogen status of burley tobacco. However analysis of PSNT fordifferent soil types might prove to be a more reliable nitrogen management tool. Cardy nitrate measurements did differ over the nitrogen rates, but there was no relationship between yield or TSNA and petiole nitrate levels during the growing season. Chlorophyll measurements did not correlate to nitrogen rates or yield.

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