Some aspects of the physiology and nutrition of tobacco

In connection with fertilizer experiments conducted in cooperation with several of the tobacco-growing states, the necessity for developing a physiological approach to the tobacco fertilizer problem, more particularly on light sandy and sandy loam soils, was well demonstrated in certain tests with potash salts at the Oxford, N.C., tobacco station which resulted in the discovery in 1923 of magnesium deficiency in these soils, accompanied by characteristic deficiency symptoms in the crop grown on them. Chemical analysis of the soils in question and of the tobacco they produce indicates that they are quite as likely to be deficient in calcium, magnesium, and sulfur as in nitrogen, phosphorus, and potassium. Field tests have shown that this is actually the case. In specific cases soil deficiency in all of these six elements has been demonstrated by (a) marked depression in yield obtained, (b) occurrence in the crop of distinctive deficiency symptoms, and (c) abnormally low content in the crop of the particular element withheld from the fertilizer. The above-mentioned soils are to be regarded simply as somewhat impure sand culture media and it is not logical, as has been very commonly done in the past, to apply to these soils salts or other substances containing two or more essential elements, without any compensating treatment, and attempt to evaluate the results obtained with plants in terms of only one of the constituent elements. With soils properly selected with respect to the above-mentioned criteria of mineral deficiency and with the precaution of varying the supply of only a single essential element, excellent data have been obtained on absorption by the plant in relation to increased supply of this element. Utilizing this plan of conducting 'field sand cultures", consistent and significant results have been obtained in extensive physiological studies of effect of the nitrogen supply on growth and development phenomena, metabolism, and other internal relations, and on the chemical and physical properties of the cured tobacco leaf. This appears to furnish a reasonably adequate procedure for study of the more tangible aspects of the mode of action of the essential elements in plant growth and associated phenomena.