Soil and Plant Factors Influencing Accumulation of Dry Matter in Burley Tobacco Growing in Soil Made Acid by Fertilizer

A field experiment was conducted to elucidate factors influencing dry matter accumulation in tobacco (Nico. tiana tabacum L. cv. ‘Burley 21’) growing in soil whose acidity was increased by fertilizer. Relatively large amounts of commercial fertilizers commonly are added to soil in burley tobacco production and knowledge of the effects of such additions on dry matter accumulation may lead to increased yields of cured leaf and improved usability of cigarette smoke. Samples of soil and plant material were obtained at varying dates during the growing season and were chemically analyzed. Varying soil pH levels were obtained from applications of N as ammonium nitrate at rates of 0, 90, 180, and 360 kg N/ha. The addition of N fertilizer to Maury silt loam soil with an initial pH of 6.2 significantly increased exchangeable Mn and decreased soil pH, exchangeable Ca, and concentrations of available MoO₄⁻² and H₂PO₄⁻. Exchangeable Mg and K were little affected by N fertilizer at any sampling date. Much of the decrease in exchangeable Ca may be attributed to leaching with NO₃⁻ by excessive rainfall early in the season. Evidence indicated some delay of nitrification of NH₄⁺ in plots fertilized at the 360 kg N rate. Nitrogen fertilization of tobacco increased concentrations of Mn in leaves, but levels were not judged to be excessive for normal growth. A tendency existed for concentrations of Ca and Mg to be decreased by N at 40 days after transplanting and concentrations were near deficiency levels for Ca at this date, although exchangeable soil Ca levels exceeded 1500 ppm. In contrast, at 77 days and at harvest, N fertilizer significantly increased plant concentrations of Ca and Mg. Molybdenum concentrations in leaves from high N plots were only 20 to 50% of those in plots unfertilized with N. Concentrations of MoO₄⁻² in leaves from fertilized plots were near deficiency levels for most of the growing season. The data suggested interaction of MoO₄⁻² and Mn, and of Mn with Ca and Mg within the plant. Correlation and regression analyses revealed significant relationships of soil measurements near transplanting and dry matter at 40 days and of plant constituents and dry matter at all dates. Results indicated the depression of dry weight by N fertilizer noted previously during early growth was the direct or indirect result of fertilizer-induced soil acidity.