Two problems are involved in the fertilizing of the land: the direct addition of plant-food, and the improvement of the physical structure of the soil. The latter office is often the more important.
Lands that, on the one hand, are very hard and solid, with a tendency to bake, and, on the other, that are loose and leachy, are very greatly benefited by the addition of organic matter. When this organic matter--as animal and plant remains--decays and becomes thoroughly incorporated with the soil, it forms what is called humus. The addition of this humus makes the land mellow, friable, retentive of moisture, and promotes the general chemical activities of the soil. It also puts the soil in the best physical condition for the comfort and well-being of the plants. Very many of the lands that are said to be exhausted of plant-food still contain enough potash, phosphoric acid, and lime, and other fertilizing elements, to produce good crops; but they have been greatly injured in their physical condition by long-continued cropping, injudicious tillage, and the withholding of vegetable matter. A part of the marked results secured from the plowing under of clover is due to the incorporation of vegetable matter, wholly aside from the addition of fertilizing material; and this is emphatically true of clover because its deep-growing roots penetrate and break up the subsoil.
Muck and leafmold are often very useful in ameliorating either very hard or very loose lands. Excellent humous material may be constantly at hand if the leaves, garden refuse, and some of the manure are piled and composted (p. 114). If the pile is turned several times a year, the material becomes fine and uniform in texture.
The various questions associated with the fertilizing of the land are too large to be considered in detail here. Persons who desire to familiarize themselves with the subject should consult recent books. It may be said, however, that, as a rule, most lands contain all the elements of plant-food in sufficient quantities except potash, phosphoric acid, and nitrogen. In many cases, lime is very beneficial to land, usually because it corrects acidity and has a mechanical effect in pulverizing and flocculating clay and in cementing sands.
The chief sources of commercial potash are muriate of potash, sulfate of potash, and wood ashes. For general purposes, the muriate of potash is now recommended, because it is comparatively cheap and the composition is uniform. A normal application of muriate of potash is 200 to 300 pounds to the acre; but on some lands, where the greatest results are demanded, sometimes as much as twice this application may be made.
Phosphoric acid is got in dissolved South Carolina and Florida rock and in various bone preparations. These materials are applied at the rate of 200 to 400 pounds to the acre.
Commercial nitrogen is secured chiefly in the form of animal refuse, as blood and tankage, and in nitrate of soda. It is more likely to be lost by leaching through the land than the mineral substances are, especially if the land lacks humus. Nitrate of soda is very soluble, and should be applied in small quantities at intervals. Nitrogen, being the element which is mostly conducive to vegetative growth, tends to delay the season of maturity if applied heavily or late in the season. From 100 to 300 pounds of nitrate of soda may be applied to the acre, but it is ordinarily better to make two or three applications at intervals of three to six weeks. Fertilizing materials may be applied either in fall or spring; but in the case of nitrate of soda it is usually better not to apply in the fall unless the land has plenty of humus to prevent leaching, or on plants that start very early in the spring.
Fertilizing material is sown broadcast, or it may be scattered lightly in furrows underneath the seeds, and then covered with earth. If sown broadcast, it may be applied either after the seeds are sown or before. It is usually better to apply it before, for although the rains carry it down, nevertheless the upward movement of water during the dry weather of the summer tends to bring it back to the surface. It is important that large lumps of fertilizer, especially muriate of potash and nitrate of soda, do not fall near the crowns of the plants; otherwise the plants may be seriously injured. It is a general principle, also, that it is best to use more sparingly of fertilizers than of tillage. The tendency is to make fertilizers do penance for the sins of neglect, but the results do not often meet one's expectations.
If one has only a small garden or a home yard, it ordinarily will not pay him to buy the chemicals separately, as suggested above, but he may purchase a complete fertilizer that is sold under a trademark or brand, and has a guaranteed analysis. If one is raising plants chiefly for their foliage, as rhubarb and ornamental bushes, he should choose a fertilizer comparatively rich in nitrogen; but if he desires chiefly fruit and flowers, the mineral elements, as potash and phosphoric acid, should usually be high. If one uses the chemicals, it is not necessary that they be mixed before application; in fact, it is usually better not to mix them, because some plants and some soils need more of one element than of another. Just what materials, and how much, different soils and plants require must be determined by the grower himself by observation and experiment; and it is one of the satisfactions of gardening to arrive at discrimination in such matters.
Muriate of potash costs $40 and upwards per ton, sulfate about $48, dissolved boneblack about $24, ground bone about $30, kainit about $13, and nitrate of soda about 2-1/4 cents per pound. These prices vary, of course, with the composition or mechanical condition of materials, and with the state of the market. The average composition of unleached wood ashes in the market is about as follows: Potash, 5.2 per cent; phosphoric acid, 1.70 per cent; lime, 34 per cent; magnesia, 3.40 per cent. The average composition of kainit is 13.54 per cent potash, 1.15 per cent lime.
The fact that the soil itself is the greatest storehouse of plant-food is shown by the following average of thirty-five analyses of the total content of the first eight inches of surface soils, per acre: 3521 pounds of nitrogen, 4400 pounds of phosphoric acid, 19,836 pounds of potash. Much of this is unavailable, but good tillage, green-manuring, and proper management tend to unlock it and at the same time to save it from waste.
Every careful gardener will take satisfaction in saving leaves and trimmings and stable refuse and making compost of it to supplement the native supplies in the soil. Some out-of-the-way corner will be found for a permanent pile, with room for piling it over from time to time. The pile will be screened by his garden planting. (Figure 121 suggests a useful cart for collecting such materials.) He will also save the power of his land by changing his crops to other parts of the garden, year by year, not growing his China asters or his snap-dragons or his potatoes or strawberries continuously on the same area; and thus, also, will his garden have a new face every year.
[Illustration: Fig 121. A good cart for collecting leaves and other materials.]
Lest the reader may get the idea that there is no limit to be placed on the enriching of the soil, I will caution him at the end of my discussion that he may easily make the place so rich that some plants will overgrow and will not come into flowering or fruiting before frost, and flowers may lack brilliancy. On very rich land, scarlet sage will grow to great size but will not bloom in the northern season; sweet peas will run to vine; gaillardias and some other plants will break down; tomatoes and melons and peppers may be so late that the fruit will not ripen. Only experience and good judgment will safeguard the gardener as to how far he should or should not go.