garded as being of less importance than potash. The results obtained at the Ohio Station' show that phosphoric acid is the most essential fertilizer for their conditions, some potash, and, in some cases, nitrogen, being also required. I found the same to be true at Briarcliff Manor, N. Y., where 100 pounds of available phosphoric acid per acre (equal to 600 pounds acid phosphate, 16-17 per cent. available) gave profitable returns. My own observations are that an excessive application of available phosphoric acid has a marked influence upon the foliage, causing it to be small, dark green, wrinkled, and apparently stunted in development, with consequently early maturity. In some cases the period of growth is reduced six or eight weeks, and consequently the yield is low; but, owing to the potatoes being mature, the quality is generally good. In certain localities, for early potatoes, where it is desirable to hasten maturity, the use of fair quantities of acid phosphate, with a limited supply of nitrogen and potash and no barn manure, is found to be good practice. The nitrogen may be supplied in an available form as nitrate of soda, since nitrification may not be active in the soil during the early period of growth. The Influence of Calcium.-Calcium does not appear to be so important as some of the other elements, although in some cases it produces a marked increase in yield (Fig. 10). If applied in a form which has an alkaline action upon the soil-as, carbonate of lime or quicklime—it may have an injurious effect by 1Ohio Bul. 125, pp. 131, 132. producing conditions which aid the development of scab. Barn Manure.-Applying barn manures is commonly practiced for potatoes with profitable results. Lawes and Gilbert' showed that only a small portion of the nitrogen of farm manures is taken up by the crop; thus, with an annual manuring of 15.5 tons per acre, containing 200 pounds of nitrogen, continued for twelve FIG. IO-INFLUENCE OF LIME UPON POTATOES Showing the influence of lime upon the yield, and that it increases the percentage of scabbed potatoes. Right, unlimed. Left, limed. Other fertilizers the same in both cases. years, but 8.3 per cent. of the nitrogen was recovered in the crop. "These results seem to indicate that this crop is able to avail itself of a less proportion of the nitrogen of the manure than any other farm crop. Yet, in ordinary practice, farm-yard manure is not only largely relied upon for potatoes, but is often applied in larger quantities for them than for any other crop." Taft, of Michigan, found that twenty-four loads of manure per acre gave the largest yield, while at the 2 1 Rothamsted Memoirs, Vol. VI. 2 Mich. Bul. 131, p. 10. Wisconsin Experiment Station twenty loads per acre were applied, and larger quantities in Great Britan. It seems natural to assume that the beneficial effects of manure must largely be due to other causes than the addition of plant-food. Among these may be its influence on the physical properties of the soil, rendering it more retentive of moisture, more porous and more permeable for air and roots, and a better home for the useful soil bacteria, which, in fact, it may supply. The decomposition of such quantities of organic matter, with the consequent liberation of carbon dioxid, aids in rendering the mineral resources of the soil more available. Generally speaking, it is more economical to apply about ten tons of manure per acre and supplement it with fertilizers, except upon loose open soils of poor texture, where the beneficial effect from the larger amount should probably be ascribed to its influence upon the retention of moisture. It is preferable that the manure be rotted somewhat and applied the previous fall, while the fertilizers may be applied when planting. On some soils, to reduce the danger of disease, it may be advisable to apply all the barn manure to the previous crop. The application of fertilizers is profitable under most conditions in the Eastern and North Central States. At New Hampshire Experiment Station the application of fifteen cords of manure increased the yield of marketable potatoes over 100 bushels per acre compared with no manure, and the use of 1,500 pounds of fertilizers with the same amount of manure resulted in a further increase in yield of 130 bushels per acre.' Taft,' of Michigan, shows that the average gain from the use of a full application of fertilizers was eighty bushels per acre. In Long Island, N. Y., a fertilizer mixture containing 4 per cent. nitrogen, 8 per cent. available phosphoric acid, and 10 per cent. potash has proven satisfactory. It is used in amounts varying from 500 pounds to 2,000 pounds per acre, and in many cases more potash is applied than is profitable. The use of 1,000 pounds of this fertilizer has given the greatest profit. Where 1,500 pounds or 2,000 pounds were used the cost of the fertilizer was more than the market value of the increased yield of potatoes. For some years I have used a mixture of 100 pounds sulphate of ammonia, 400 to 600 pounds acid phosphate (16 to 17 per cent. available), and 100 pounds muriate of potash with eight to ten tons of partially rotted manure per acre on a medium loam soil. At New Hampshire Experiment Station' 300 pounds muriate of potash per acre gave the best results when compared with none, 150 pounds, and 450 pounds per acre. The above mixtures merely show quantities used by certain individuals; each farmer must work out a mixture suited to his needs. There are other conditions than the application of fertilizers. As Dr. W. H. Jordan' pithily puts it: "It is clearly evident that a large supply of plant-food does not necessarily insure a satisfactory crop. Other conditions which largely pertain to culture-such as texture, humus, and watersupply-exercise a controlling influence, and wher these conditions are unfavorable their effect is not overcome by heavy applications of fertilizer." 1 N. H. Bul. III, p. 115. 2 (N. Y.) Geneva Bul. 187, p. 215. It almost invariably occurs that potatoes grown without any manure mature earlier and contain more dry matter, with a correspondingly reduced yield,' than those grown on land manured with barn manures or a complete fertilizer. The vigorous growth induced under the latter conditions cannot be matured in the same time, hence for an early crop it is unwise to stimulate too vigorous growth. The Function of Fertilizers. The prevailing opinion in purchasing fertilizers is that they contain a certain amount of plant-food-usually nitrogen, phosphoric acid, or potash-in a more or less available form, and that the benefits received from their application is due to the addition of this plant-food to the soil. So deeply seated is this theory that all fertilizers are bought and sold on this basis, and laws controlling the business have been formulated upon it. The ingredients-nitrogen, phosphoric acid, and potash, with others-are necessary for the growth of all crops, but the amounts of the essential ingredients, other than the above mentioned, are believed to be present in the soil in sufficient quantities to meet all the requirements of the crops grown. A 300-bushel crop of potatoes has been found to contain 81 pounds of nitrogen, 30.6 pounds of phosphoric acid, and 79 pounds of potash. Taking 49 New York soils, the chemist found that the surface eight inches contained, per acre : 2 3,053 pounds, enough for 38 crops Nitrogen 1 Va. Bul. 92, p. 107. 16,317 66 2 (N. Y.) Cornell Bul. 130, p. 157. |