CHAPTER V

MANURING AND FERTILIZING

LAND is manured and fertilized either to increase or to maintain its crop-producing power. Whether this is secured by the direct effect of the chemical ingredients in the manure or fertilizers, or by their influence upon the physical properties of the soil, or both, is an unsettled scientific problem, but all agree that under certain conditions the addition of manures, fertilizers, and water to the soil is profitable. Whether it will be profitable on a particular farm or field, and the manure, fertilizer or combination of fertilizers which will be most profitable to use, are questions the grower must settle for himself by trial. No chemical examination of the soil yet conducted has shown why two soils, apparently identical in chemical composition, should not produce similar yields of crops. Experience has shown that the chemical composition of the soil is no guide to its crop-producing power. Hence, all that can be given in this chapter is to submit mixtures of fertilizers that are used and the rôle the different important ingredients are believed to play in the plant economy.

In addition to water, which is treated elsewhere, four elements are frequently applied in various chemical forms as fertilizers-nitrogen, phosphorus, potassium, and calcium. The potato through its life requires liberal supplies of the first three of these elements, and its behavior in regard to these is similar to that of

a shallow-rooted root crop. The facts that the potato is a starch-producing crop, and that its period of growth is through the summer and extending well into autumn must be remembered. In these features it is

similar to corn, but distinctly different from the cereals which ripen in the summer, as it is assumed that it is able to utilize the nitrates and other plant-food liberated during the summer and fall. E. Hecke1 states that the demand for nitrogen is especially strong during the first half of the vegetative period, while the demand for potash is greatest during the second half of the growing period, and that potash aids in the formation of starch, and especially in the development of tubers and roots, although the effects were observed in all parts of the plant.

The Influence of Nitrogen.-Wilfarth' showed that when the supply of nitrogen is insufficient the leaves tend to turn yellow, and that if the available supply of potash is deficient heavy applications of nitrogen tend to reduce the percentage of tubers and starch. Lawes and Gilbert' show that nitrogen stimulates the production of starch, provided the mineral constituents are not deficient; but in large quantities nitrogenous fertilizers stimulated luxuriant growth, delayed maturation, and produced potatoes richer in nitrogen and much more liable to disease. At the Rhode Island Experiment Station' dried blood ranked first of the nitrogenous fertilizers applied, followed by nitrate of soda and sulphate of ammonia; but on soils said to be extremely acid, dried blood was only about half as

1 E. S. R., VII., p. 667.

Rothamsted Memoirs, Vol. VI.

2 E. S. R. XIV., p. 561.

R. I. Bul. 65, pp. 133, 134.

beneficial as it should be; hence, such soils need liming before full benefit can be derived from the use of this fertilizer. A mixture of two-thirds dried blood and one-third nitrate of soda, or of equal parts of all three fertilizers, is suggested. At the Tennessee Experiment Station' cottonseed-meal was found to be a more profitable source of nitrogen than nitrate of soda, while at the Florida Station' the nitrogen of cottonseed-meal and castor pomace were equally effective, but that of nitrate of soda was more so by 30 per cent.

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The Influence of Potash.-Wilfarth and Wimmer show that when potassic fertilizers are applied to a soil almost destitute in potash they

1. Increase the size of the tuber, but have little influence upon its composition, and that the amount of potash in tubers remains fairly constant, uninfluenced by the amounts in the soil, or applied, unless very heavy applications are made, which may cause an increase to a certain point, but will be attended by a decline if continued.

2. Decrease the percentage of stems and leaves, but have no marked influence on the roots of potatoes. 3. Have a marked influence on the shape and appearance of the leaf; if deficient, the leaves are yellowish-brown in color, and become spotted or striped in the portions between the veins, while the petiole of the leaf and ribs retain their dark green color. If the supply of potash is insufficient the leaves tend to curl, and sometimes collapse of the plant follows.

1 Tenn. Bul., Vol. XIII., No. 3, p. 6. 3 E. S. R., XIV., p. 561.

2 Fla. Report, 1900-1901, p. 27.

4. Increase the quantity of water transpired per gram of dry matter.

Hecke' shows that the application of potassic fertilizers has a marked influence in the production of tubers and roots, and that potash assists in the formation of starch. Lawes and Gilbert' noted that the percentage of potash was relatively high when the supply of it was relatively liberal and vice versa, but the variations are small, and that where there was a deficiency of potash in the supply and in the ash there was generally an increased supply of lime in the ash.

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Which is the Better Source of Potash, Sulphate or Muriate of Potash ?-This question is still unsettled, because, apart from other considerations, one of the deciding factors is the relative cost of each. In many cases the results are inconclusive, while in some cases the fertilizers appear to be of equal value. In others sulphate of potash gave better results; thus Davidson, of Virginia, found that the potatoes grown by sulphate of potash contained more dry matter but a less percentage of starch than those fertilized with muriate of potash. Brooks' found that sulphate of potash gave a greater yield per acre of merchantable tubers, which were of larger size and of superior eating quality, containing 2 to 3 per cent. more starch, and, when cooked, the potatoes were whiter, of better flavor, and more mealy.

1 E. S. R., VII., p. 667. 2 Rothamsted Memoirs, Vol. VI., "Experiments on the Growth of Potatoes." 3 (N.Y.) Geneva Bul. 137, pp. 604, 620. 4 N. H. Bul. 41, p. 13. 5 Mass. (Hatch) Report, 1896, p. 22; R. I. Bul. 65, p. 133; Mich. Bul. 131, p. 10; (N. Y.) Geneva, Bul. 137, pp. 621, 622. 6 Va. Bul. 92, pp. 107, 108. 7 Mass. (Hatch) Report, 1904, p. 122.

The time and method of application must be considered. In my experience muriate of potash has given better results when applied the previous fall, especially if more than 100 pounds per acre are to be applied, the presumption being that the potassium compound undergoes changes in the soil, and that the injurious chlorine is removed as a chloride by the winter and spring rains. For spring application in the drills sulphate of potash may be better, or a mixture of sulphate and muriate of potash, if more than the above-mentioned quantity is required. The disadvantage of the muriate of potash seems to be due to the fact that it is a chloride, and Sjollema1 and Pfeiffer' have shown that the chlorides of potassium, sodium (common salt), and magnesium, when added to the sulphate of potash, diminished the starch content of the potatoes considerably, and that the reduction was greatest in varieties rich in starch. This would seem to support the common idea that sulphate of potash produces better quality potatoes than muriate of potash. Wheeler," of Rhode Island, shows that calcium chloride had a marked poisonous effect upon potatoes and nearly destroyed them, while the same amount of calcium in certain forms other than the chloride or sulphate increased the yield and vigor of the plants. New varieties, and those making a heavy growth of haulm, seem to be particularly sensitive to chlorides.

Influence of Phosphoric Acid.-Lack of phosphoric acid is accompanied by dark green leaves. While phosphoric acid aids starch formation, it is often re

E. S. R., XII., 434. E. S. R., XII., 443. R. I. Bul. 40, pp. 85, 86.