The necessity for more definite knowledge concerning the actual wants of the tobacco plant in the matter of food, led to an investigation of the subject some years ago by Prof. S. W. Johnson on behalf of the Connecticut State Board of Agriculture, and more recently by Schiffmayer for the Agricultural Department of the Madras Presidency.
Prof. Johnson aptly observes it to be “a well-established fact that plants may receive from the soil and retain a larger portion of ash-ingredients than is needful for nutrition. This is especially marked in case of the lime, potash, and soda salts. The excess of these substances thus taken up may either be deposited in the solid state in the cells of the plant, or may remain dissolved in the juices. In tobacco, a part of the nitrogen usually exists as a nitrate, in combination with potash. That is to say, portions of the nitrogenous food of the plant—the nitrates of the soil—are not completely worked over into albuminoids, and into nicotine, the nitrogenous constituents of tobacco, but accumulate and remain in considerable quantity in the sap. When a dry tobacco-leaf is set on fire, it often burns like ‘touch paper’ (paper soaked in a solution of saltpetre and dried) with bright sparkles of fire, indicating the points where the nitre has gathered in minute crystals as the juice of the leaf evaporated. The quantity of superfluous salts in the plant depends upon its succulence, and upon the supply of them in the soil. Doubtless certain definite amounts of potash, lime, magnesia, iron, sulphuric acid and phosphoric acid are absolutely necessary to produce a given weight of tobacco. In case several or all these substances are superabundant in the soil, the plant has no power to exclude any unnecessary surplus of one or all of them from its interior altogether, although there are good reasons known to prevent their entrance beyond a certain limit. In one soil potash may be relatively most abundant, and may for that reason be found in the crop in greater quantity than was necessary for the growth of that crop. In another soil lime may be in surplus, and there the crop may have the minimum of potash, and a considerable excess of lime.
“The crop is a result of the working together of a number of causes or conditions; these are the heat and light of the sun, carbonic acid and oxygen of the atmosphere, water, nitrates and ammonia, and the ash-elements enumerated in our table of analyses. The crop is limited in quantity by that condition of growth, which is presented to it most sparingly. The richest and best prepared soil without solar warmth, or without due supplies of rain, cannot give a crop, and if weather be most favourable, then in one field it may be too little potash, in another too little phosphoric acid, in another too little nitrogen, which lowers the yield, or reduces the quality of the product.
“It is usual in tobacco culture to manure very heavily, and in many cases it is probable that all the various forms of plant food are present in available abundance. But soils differ in the nature of the supplies which they are able to yield to crops, and fertilizers even, when the same in name, may be very unlike in fact. The chief reliance of the tobacco farmer is stable manure. This, however, is by no means uniform in origin, appearance, evident quality, or chemical composition. The manure from bullocks, wintered on hay and roots, is very different from that of horses maintained chiefly on oats or corn. The yard manure that contains much strawy litter or much wasted hay, differs again from that of the city stables, from which the straw is carefully raked out to be used over and over again for bedding. The farm-made manure is likely to be much richer in potash and lime, and the city manure is richer in phosphates and nitrogen. Yet in the reports of the farmer, these two essentially different fertilizers are designated as stable manure simply.
“Every one understands that a fertilizer acts upon the plant to supply it with food, and to favour its growth; everybody is also convinced that some fertilizers act upon the soil, improving its texture and composition and increasing its fertility. It is an equally well ascertained fact that the soil acts upon fertilizers to modify their effect. A very wet or very dry soil is known to nullify the benefit which might be expected of a fertilizer in a simply moist soil; but more than this, more than by the accident of external circumstances, it is a fact that each kind of soil has a special action of its own on fertilizers, so that if it were asserted of two soils, which, unmanured, were of equal fertility, that a given fertilizer applied to both, greatly improved the crop on one, and had little effect on the other, such a statement might not only be accepted as a fact, but an explanation might be given in general terms for such a fact.
“Now experiments have shown that different soils when mixed with like quantities of various fertilizing elements and then treated with water, in imitation of rain, manifest very different behaviour toward the admixed substances. One soil will lay hold of the potash in a fertilizer, and fix it in a kind of chemical combination so firmly that water can dissolve it but with extreme slowness; another soil puts its grasp on the lime of a fertilizer, and at the same time allows potash which belongs to itself to be dissolved out freely. There is, in fact, always a complicated series of changes set in operation whenever any fertilizer is incorporated with the soil, be it animal, vegetable, or mineral; be it alkali, acid, or saline; be it made on the farm or imported from abroad; be it natural or artificial. The fertilizer acts on the soil, and the soil reacts on the fertilizer; but the point we wish to make prominent is this, that different soils are differently affected by one and the same application, or in other words, a given manure fertilizes a given crop unequally in degree, and unlike in kind, on different soils, by virtue of the different assimilating or fixing power, which the soil exerts upon its ingredients.
“We know of the existence of these peculiarities of soils, and something of their causes and of the laws by which they act; but the real necessities of the tobacco crop, or of any other crop, as respects soil-ingredients, cannot be arrived at by chemical analysis of a single sample, nor of a dozen samples.” Thus analyses of a dozen New England tobaccos showed the following highest and lowest percentages of each ash-ingredient, and of nitrogen:—
| Silica | 0·05 | to | 0·30 | Magnesia | 0·94 | ” | 2·21 |
| Chlorine | 0·08 | ” | 2·55 | Potash | 3·90 | ” | 7·45 |
| Sulphuric acid | 0·52 | ” | 1·69 | Soda | 0·08 | ” | 1·81 |
| Phosphoric acid | 0·47 | ” | 0·80 | Nitrogen | 3·20 | ” | 5·11 |
| Lime | 3·17 | ” | 8·22 |
“It appears that the percentages of nitrogen, phosphoric acid and potash are nearly twice as great in some samples as in others; that the proportions of magnesia and lime are about 2½ times greater in some samples than in others, and that sulphuric acid is 3 times more in one case than in another. The variation of silica is still greater, and the disparity rises to its extreme in case of soda and chlorine, whose maxima are respectively 20 and 30 times greater than their minima.”
The three ingredients chlorine, silica, and soda cannot be considered in the light of essentials to tobacco culture; but the other substances are absolutely indispensable to plant growth, and the absence of any one of these would render a soil incapable of sustaining agricultural vegetation of any kind. “The variation in the percentage of these ingredients depends somewhat upon the fact that the leaves of different crops are unequally developed, and therefore their nutritive needs are unlike; but it is, no doubt, chiefly connected with the fact that the plant takes up from a highly fertilized soil more of each or every element than is essential for growth. The nearly certain conclusion is that every one of the crops analysed contains more of some elements than belongs to its nutrition. It is quite certain that the average of the analyses of the New England tobaccos is fully up to the mark as regards the necessities of the crop. It is, indeed, not improbable that the lowest percentages of each ingredient are quantities sufficient for a perfect crop. Still, it is not proved that lime may not partially take the place of potash, or the reverse. The probability of such a substitution is great upon the face of most of the analyses. As a rule, those which show most potash show least lime and vice versâ; but in one sample both ingredients are considerably below the average. The practical issue of these considerations is to give great probability to the view that the tobacco crop is fed unnecessarily (and wastefully?) high.” (Prof. Johnson.)