Yield and quality of Virginia tobacco as influenced by genotype and agricultural practices

The effects of three N rates (0, 20 and 40 kg N ha-1) and time of topping (topping at early flowering and topping at full flowering) on yield and quality (percentage of first, second and third grade dried tobacco, and chemical composition) of Virginia tobacco genotypes (Virginia 0514, Hybrid 33, Hybrid 27) were studied in field experiment in 2015-2016. The experimental design was a randomized complete block replicated three times. The most important factor that affects leaf yield was N rate. Genotype differences and time of topping also had a significant effect on the yield. The application of 20 and 40 kg N ha-1 improved the leaf yield by 12.6%, and 17.8%, respectively, in comparison with unfertilized plants. When tobacco was topped at early flowering stage, the yields of the different genotypes increased by 4.3%-10.1% compared to the topping at full flowering. Nitrogen fertilization and topping had almost the same effect on the quality of the tobacco (as determined by the percentage of first grade dried tobacco). The genotype effect was weaker but also statistically significant. The quantity of the first class was also determined by the interaction of topping and nitrogen rate. Topping at early flowering increased the concentrations of nicotine and total nitrogen in tobacco. The reducing sugars/nicotine ratio was higher, and in this case more favorable, when tobacco plants were topped at full flowering stage. Nicotine content (2.33%-3.53%) increased when the rate of nitrogen increased. There was a negative relationship between increasing N levels and reducing sugars content.