CORESTA Congress, Online, 2020, Agronomy/Phytopathology Groups, AP 15

Nitrogen fertilizer source and the impact to flue-cured tobacco nutrient assimilation, yield, quality, value, and chemistry

North Carolina State University, Department of Crop & Soil Sciences, Raleigh, NC, U.S.A.

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.