Effects of Micronutrient Deficiencies on Mineral Composition, Nitrogen Fractions, Ascorbic Acid and Burn of Tobacco Grown to Flowering in Water Culture.

Abstract

Connecticut Broadleaf tobacco was grown to the flowering stage during spring and fall in the greenhouse at about 25[degree]C. The fixed-charge, depletion method was used. Each plant was grown in 10 1 of a purified nutrient solution adjusted for maximal yield and minimal ion content in spring. The calcium carbonate method was used to remove trace element impurities from the nutrient solution. Yield tests were in triplicate; and analyses with composite samples. Loss of elements from solution, nitrogen fractions and ascorbic acid in the leaf, and burn of cured leaf were determined for deficiencies of Fe, Zn, Cu, Mn, B and Mo. Nitrogen fractions were estimated by the Kjeldahl method and its modifications; and P, K, Ca, Mg, Fe, Cu, Mn, B, Na and Al spectrochemically. Variations in S, Zn and Mo were not estimated. It was found that assumed absorption of biologically essential elements from the complete basal solution, adjusted for maximum yields with minimal supply of salts in the spring, was affected by the plant without change in proportion of solution components ("economical" solution of Hoagland). Assumed absorption of minerals from the solution by the control plants in the spring approximated 93% or more. Decreased yields, irrespective of micronutrient deficiency type or low light in fall, caused approximately proportionally increased mineral content in plant and leaf. This yield-supply factor was important with relation to mineral and organic content of the plant, and served as an aid in distinguishing between specific and general effects of micro-nutrient deficiency. Micronutrient deficiency affected essential element proportions in the leaf to a greater extent than in the plant as a whole. Micronutrient deficiency, except Cu, led to an increased content in the leaf of nitrate and free amino acids and a decrease in protein. Diminished growth caused by deficiency led to decreased production of ascorbic acid in the leaves. Boron and Mo deficiencies were especially effective despite comparatively high yields. Duration of glow when ignited without flame ("burn") of air-dried ("cured") leaf was increased by B and Mn deficiencies.