It is not uncommon to find market gardens managed successfully without the use of commercial fertilizers. In all such cases stable manures and perhaps night soil are applied in liberal quantities. Although it is possible to make large profits when fertilizing with manures only, it is doubtful whether there are any instances when commercial fertilizer in some form could not be used to advantage. Manure is an unbalanced ration; it is richer in nitrogen than in mineral elements and there is likely to be a surplus and, therefore, a waste of nitrogen when it is applied without corresponding additions of potash and phosphoric acid.
The most forceful argument for the use of commercial fertilizers is the inadequate supply of animal manures. While hundreds of market gardeners near the cities depend mainly upon stable manures, thousands of truckers remote from the great sources of supply must resort to the use of commercial fertilizers in order to secure maximum returns.
There are other reasons for the use of commercial fertilizers. Stable manure must undergo changes before it is accessible to plants, while some of the commercial fertilizers are immediately available when incorporated with moist soil, a characteristic which gives chemical fertilizers a great advantage over stable manure, for it is possible to mature crops in less time by their use than can be done with manure alone. Rapid growth is of immense importance in commercial vegetable gardening. Therefore, with the aid of commercial fertilizers the gardener may be able to harvest several crops from the same ground in one season, to clear the land in time to start a cover crop or mature a green manurial crop before cold weather, and to secure far better quality than is possible when the growth is slow. The quality of many vegetables is closely associated with rapidity of growth. A slow growth is likely to cause a bitter flavor in lettuce, a sharp flavor in onion and a pungent flavor in radish. Again, slow growth is certain to cause greater development of fiber, making the vegetables tough, woody or stringy. A rapid growth usually secures succulence, crispness and palatability. And, in addition, rapid-growing vegetables are less subject to injury from insects and diseases than are slow-growing ones.
Of the three elements supplied by commercial fertilizers to garden crops, nitrogen is more frequently the limiting factor than either potash or phosphoric acid, because in cultivated soils it is lost more quickly and, also, because it is more expensive to buy, and therefore likely to be supplied in less abundance. Nitrogen plays the most important part in the growth of leaves and succulent stems, and therefore it is particularly valuable in the production of such crops as cabbage, lettuce, brussels sprouts, spinach, kale, swiss chard, endive, celery, sweet corn and asparagus. Also, large amounts of nitrogen are very necessary in growing onions.
Nitrogen is valued largely according to its availability. For this reason nitrate of soda is considered by commercial growers the most valuable nitrogenous fertilizer. It is available to the plant as soon as dissolved, while stable manures, dried blood, tankage, bone meal and other organic materials must rot or decay before they are of any benefit as plant foods. For the money invested probably no other fertilizing material is capable of giving such large net returns, provided all conditions are satisfactory for its use. Many experiments have been made at the New Jersey station, and one of the bulletins (N. J. Sta. Bul. 172, p. 11), which reports the results, contains the following statement: "It is quite possible to have a return of $50 an acre from the use of $5 worth of nitrate of soda on crops of high value, as, for example, early tomatoes, beets, cabbage, etc. This is an extraordinary return for the money invested and labor involved; still, if the value of the increased crop from its use was but $10, or even $8, it should be regarded as a profitable investment, since no more land and but little more capital were required in order to obtain the extra $5 or $3 an acre. It is the accumulation of these little extras that oftentimes change an unprofitable into a profitable practice."
The amount of nitrate of soda applied to the acre at any one time may vary from 100 to 250 pounds. Larger applications are sometimes made, but they are of doubtful economy. The better and safer practice is to make frequent applications of smaller quantities.
There are no rules concerning the frequency of applications, but it depends upon the fertility of the soil, the character of the crop and the time of planting. Nitrate of soda is especially valuable for early spring applications before soil nitrification becomes active. If used when the ground is cool it may be the means of encouraging a rapid growth when all other agencies fail. A common practice is to see that some nitrate is contained in the fertilizer applied before planting. After two or three weeks a second application of the nitrate can often be made with profit, and additional ones are frequently advantageous. For more specific information on this question see Chapter XXI (Cultural Directions. Artichoke, Asparagus) on the cultivation of different classes of vegetables.
The following methods may be employed in applying nitrate of soda: (1) It may be applied alone or mixed with other fertilizers before sowing or transplanting. If the soil does not contain a large percentage of sand, the loss from leaching is not likely to be serious. (2) As a top dressing around the plants or along the rows. This may be done by hand or when space will permit with a side-delivery fertilizer distributor. (3) In dry weather it is an advantage to open furrows along the rows, distribute the nitrate in the furrows and then close them with a small shovel or hiller; the same purpose may be accomplished by the use of a drill; or even by cultivation, after an application on the surface, the fertilizer may be mixed thoroughly with the moist soil. (4) The quickest and easiest way to apply this salt is to sow by hand with a full swing of the arm, as when sowing clover seed, letting the fertilizer fall where it will. Many gardeners who have adopted this labor-saving plan claim that it is safe in fertilizing plants, even those which have tender leaves, provided the foliage is perfectly dry, for every crystal that strikes the leaves naturally rebounds or glances to the ground. The broadcasting method is safe for cabbage, even if the salt lodges in the axils of the leaves. (5) Nitrate may also be dissolved in water and then applied by means of a hose; or better, by the Skinner system of irrigation. One ounce of nitrate to one gallon of water is the proper proportion for most purposes. If there is fear of burning the foliage, clear water may be sprayed on the plants after the solution of nitrate has been applied.