Nitrogen fertilizer source and the impact to flue-cured tobacco nutrient assimilation, yield, quality, value, and chemistry
The impact of nitrogen (N) fertilizer sources to macro, secondary, and micronutrient assimilation at various growth stages and their impact to post-harvest measurements have not been reported in flue-cured tobacco. Research was conducted in 2016 and 2017 to test the effects of four N fertilizer sources (calcium nitrate, calcium ammonium nitrate, liquid urea-ammonium nitrate, and ammonium sulfate) on these parameters. Foliar concentrations of total N, phosphorus, magnesium, and chloride were not impacted by N source in green or cured leaf samples. In contrast, foliar nitrate, potassium, and sulfur concentrations were sometimes influenced by N treatment. Results were variable; however, visual nutrient deficiencies were not observed nor were they analytically identified, thus indicating that nutrient assimilation was sufficient. In contrast, foliar boron concentrations were identified as deficient in all treatments 3 weeks after transplanting and at layby. Applications of urea-ammonium nitrate reduced boron concentration by ≈ 2 to 4 mg kg-1 relative to other N sources two weeks after layby and at flowering, with only the latter below the established sufficiency minimum of 18 mg kg-1. However, visual symptoms of boron deficiency were not observed. Calcium concentration was greatest in treatments comprised of calcium nitrate, which provided an additional 95-112 kg Ca ha-1, depending on environment. Residual soil calcium was 10-times greater than what is required for maximized growth; therefore, the slight increase in calcium uptake has little practical value. Foliar calcium concentration was deficient two weeks after layby (< 0.75 %) and was borderline deficient at flowering, regardless of treatment. Cured leaf concentration was remarkably higher, thus indicating that deficient calcium concentrations are often transient and will recover post-topping. Overall, these differences are likely to be of little concern as cured leaf yield, quality, value ha-1, price kg-1, and total alkaloids and reducing sugars were similar among all N sources. Nitrogen fertilizer source appears to have little practical effect on the assimilation of macro, secondary, and micronutrients, regardless of N source. While nutrients, such as Ca and B, were deficient at different stages of growth, visual symptoms of deficiency were not observed nor were post-harvest measurements impacted. Based upon these results, commercial farmers have great flexibility in regards to N source selection.