Comparing Application Methods for Boron Fertilizer on the Yield and Quality of Tobacco (Nicotiana tabacum L.)

The present study is based on the hypothesis that different methods of supplying boron (B) may have different effects on the yield and quality performance of tobacco crop. A field experiment was conducted to study the effect of different methods of B fertilization on the yield, quality, and leaf composition of flue-cured Virginia tobacco (cv. K-399) in 2007 at the Pakistan Tobacco Research Station, Mansehra. Three different methods (i.e., foliar spray, soil application, and root dipping at the rates of 0.25 kg ha-1, 1 kg ha-1, and 0.5 mg B L-1, respectively) in the form of boric acid along with a control (where no B was applied) were used in a randomized complete block design and replicated four times. Results revealed that different methods of B application significantly affected tobacco yield, quality, and nutrient uptake compared to the control. Maximum leaf area of 707 cm2, green leaf yield of 18553 kg ha-1, cured leaf yield of 2314 kg ha-1, grade index of 79%, nicotine content of 2.54%, and sugar content of 18.35% were noted in the treatment plot where B was applied as a foliar spray; however, in a few cases, there was no significant difference found among different methods of B application. Chloride and potassium contents were not significantly affected by any method of B fertilization. The B fertilization increased the concentration of this element in tobacco leaf, and a maximum concentration of B 48.55 mg kg-1 was noted in the foliar spray treatment. Moreover, fertilizer-use efficiency for different methods of B application revealed that foliar spray is more efficient as compared to soil application and root-dipping methods. Nutrient ratios to B such as potassium (K) / B and chloride (Cl) / B considerably decreased in tobacco leaf with increases in the concentration of B in leaves. These ratios provided some indication of the interrelationship of B with these nutrients in tobacco plants. Results also revealed that K/B and Cl/B ratios closely correlated with the grade index of tobacco leaf, and good grades of tobacco were found to be at a K/B ratio of 682 and a Cl/B ratio of 148 under the experimental conditions. The overall results indicated that the B foliar spray at the rate of 0.25 kg ha-1 significantly increased the yield, quality, and the nutrient uptake by the tobacco crop under the prevailing conditions and was more effective than other methods of B application.