Tobacco is usually characterized as a very exhausting crop. This is not true as regards the amount of nutriment taken from the soil, for in this respect tobacco is less exacting than hay, potatoes, or rye. It demands chiefly potash and lime, with phosphoric acid and nitrogen. Prof. Johnson recommends for the manuring of one acre, besides ploughing in the stalks of the plants, 500 lb. rock guano or 800 lb. fish guano, 500 lb. kainit (potash salts), and 50 lb. quicklime. But surely it cannot be advisable to mix quicklime with an ammoniacal manure like guano; it seems to the writer that gypsum, or spent calcium oxide from gasworks, would be a far preferable medium for conveying lime to the soil.
As observed by Johnson, the “demand made on the soil or on fertilizers by the tobacco crop, is for certain reasons greater than that made by other crops which receive more of nearly every kind of plant food. Hay is more exhausting than tobacco as measured by total export from the soil, but grass grows the whole year throughout, save when the ground is frozen or covered with snow, or for more than 8 months. The period of active growth which is required to mature a hay crop, begins indeed in April, and is finished by July, a period of 3 months, but during the year previous, for at least 5 months, in case of the first crop, the grass plants have been getting a hold upon the soil, filling it with their roots, and storing up food in their root-stocks or bulbs, for the more rapid aftergrowth. Tobacco on the other hand cannot be set out in the field before about the 10th of June, and should be in the shed in about 3 months. Its growth then must be a very rapid one, and the supplies of food in the soil must be very abundant so that the quick-extending roots may be met at every point with their necessary pabulum. A crop of 1260 lb. dry leaves requires about 1100 lb. of dry stalks to support the leaves, making a total of 2360 lb. of dry vegetable matter. As new hay contains not less than one-sixth of moisture, we increase the above dry weight of the tobacco crop by one-sixth, to make a fair comparison, and obtain as the yield of an average tobacco field 2750 lb. of air-dry vegetable matter, or more than 1⅓ tons. The matter stands then thus: An acre of first-rate grass land yields as the result of 8 months’ growth, 2¾ tons of crop, while the tobacco land must yield 1⅓ tons in 3 months.
“If the above data are correct, the average rate of growth of tobacco is greater than that of a corresponding hay crop, in the ratio of 9:7. The real disparity is, however, much greater. The principal growth of tobacco is accomplished in the hottest summer weather, and in a period of some 40–50 days. Very heavy manurings are therefore essential to provide for its nourishment, and the more so because the best tobacco lands are light in texture, and may suffer great loss by drainage, evaporation, and decomposition.”
From these premises, Prof. Johnson advances to the question of what should or should not be presented to the plant in the form of manure. He commences with a caution that, in general, growers must “avoid employing fertilizers which contain salt or other chlorine compound in raising wrapping or smoking tobacco. It is evident, also, that there is no occasion to use any fertilizer for the special object of supplying phosphoric acid, since the heaviest export of this substance does not exceed 10 lb. per acre, annually. It may be well to mention here that phosphates which may be put upon a tobacco field, in guano, &c., cannot suffer waste by washing out, and will come to use when grain or grass shall follow in the rotation.”
He observes of gypsum (lime sulphate) that it is “a valuable application to tobacco, not because it is very largely taken up by the crop, for the greatest export of sulphuric acid, viz. 20 lb. per acre, is restored by 50 lb. of plaster, and the greatest export of lime, 120 lb., is made good by 400 lb. of the sulphate, but because lime sulphate dissolves in 400 times its weight of water, and may rapidly wash out of the porous tobacco lands, and especially because the solution of lime sulphate in the soil is a very effective agent in rendering soluble and accessible to crops the potash and magnesia, which too often exist in close-locked combinations. The average annual rainfall (snow included) in our latitudes, is no less than 10,000,000 lb. per acre. This enormous quantity of water would be enough to dissolve and wash out of the soil 25,000 lb. of gypsum per acre if it had time to saturate itself, and then flowed off. In fact, but a small proportion of the rainfall runs through and out of the soil, not more than 10 to 20 per cent., according to its porosity and situation; but it is plain that there is nothing to hinder the waste of a hundred pounds or more of gypsum per acre yearly, Since all investigations go to show that the soil has no retaining power for lime sulphate as it has for potash and for phosphoric acid. In Nessler’s experiments, gypsum had an excellent effect on the burning quality of the tobacco raised under its application, an effect attributable, he believes, to the fact that this fertilizer often liberates potash in the soil, as Liebig and Deherain have demonstrated, and is therefore equivalent to an application of potash, provided the latter actually exists in the soil.
“Potash is exported in the tobacco crop to the amount of 70–80 lb. per acre yearly, and is required for the stalks to the extent of some 50 lb., making a total of 120–130 lb. As already intimated, potash does not commonly waste from the soil by washing. It is seldom found in appreciable quantity in well or drain water, and most soils absorb it and fix it so firmly that water can remove it but very slowly. It does, however, appear in the drain water from very heavily dunged fields, though in small proportion. Stable or yard manure on the average contains one-half per cent. of potash, or 10 lb. per ton. Twelve or thirteen tons of stable manure would therefore contain the potash needful to produce a crop. The dressing of 20 tons of 10 cords of stable manure, per acre, which is often employed on tobacco, is doubtless enough to fully supply the crop, and the application of additional potash is apparently quite unnecessary. The employment of potash salts upon tobacco lands would therefore seem to be uncalled for unless the amount of stable manure is greatly diminished, or its quality is very inferior. In case potash salts are to be applied, the best form to make use of is potash sulphate, of which 250 lb. contains 135 of potash. Next to this is probably potash carbonate, i. e. the ordinary potash of commerce, which contains some 70 per cent. of potash; 200 lb. of this would be sufficient for an acre. To apply it I would suggest breaking it up into small pieces and soaking it in two or three times its weight of water until the lumps crush easily, and mixing these with so much ground gypsum as will make a mass dry enough to handle.
“Kainit, which contains some 15 to 20 per cent. of potash, but also 10 per cent. or more of chlorine, is not so good for leaf tobacco, and least of all to be recommended is potassium chloride (muriate of potash) which is nearly half chlorine.
“Magnesia is an element which is abundantly provided for in stable manure, every ton of which, according to analyses on record, contains some 3 lb. of this substance.
“Lime is supplied in relative abundance in stable manure, the average ton of which contains some 15 lb. We have seen that 600 lb. of gypsum contain as much lime as the average tobacco crop: guano, dry fish, and superphosphate, each contains some 5–10 per cent. of lime. There is, furthermore, little likelihood that any soil intended for tobacco would not of itself contain enough lime to support the crop. Lime in the caustic state has, however, a value independent of its direct nutritive power, which is well worth the attention of the tobacco raiser. Of this I shall write briefly in a subsequent paragraph.
“Nitrogen in absolutely dry New England tobacco leaf ranges from 3·2 to 5·1 per cent., or 4·24 as the average. This is a larger proportion than exists in any of our ordinary field crops, except the seeds of legumes. The grain of wheat and red clover hay contain when dry scarcely 2½ per cent., and they exceed all other usually raised vegetable products, except the leguminous seeds. The pea and bean contain, when dry, 4·5 to 4·7 per cent. of nitrogen. The acreage export of nitrogen is nevertheless not large according to the data of our tables. It should be remembered, however, that the average is derived from 5 samples only.... There are reasons to suppose that this result is too low. Furthermore it is not improbable that tobacco loses nitrogen during the curing process.”