Every type of real soil contains all the elements of plant growth. This plant food results from a breaking down of soil particles and the setting free of chemical elements which, either singly or in combination, serve as food for plants.
Whatever the type of soil may be, it will be found that certain crops will make better growth in it than others. As a general rule, it may be said that the only way to determine which plants will grow best on a given soil is by the trial-and-error method. However, by observation of the growth on similar types of soil we can learn something of a soil’s crop adaptability. There are some crops that will grow in almost any soil and there are others that need an exactness of texture, moisture and plant food which makes them highly specialized products. The operator must learn how to work in harmony with the peculiarities of his own soil before he can hope to get the best results.
In acquiring a tract for the growing of plants of any kind it is desirable to get a soil type that will meet the requirements of most plants. As a general rule, this type contains enough clay to be retentive of moisture, enough sand to be easily worked and is generally suitable for bacterial growth. In other words, what is commonly called a loam is the ideal type for general agricultural and horticultural purposes. This may be a heavy loam, in which clay predominates, or a so-called light loam, in which sand particles predominate. An examination of a handful of soil by a person experienced in farming will indicate its nature and its adaptability to ordinary crop production.
Essential Elements of Plant Food.—Countless scientific experiments in plant growth show that potassium, lime, phosphorus, magnesium, iron, sulphur, nitrogen, carbon, oxygen and hydrogen are essential to normal development. The carbon, hydrogen and oxygen elements make up nearly 99 per cent of the entire composition of the plant and are derived from the atmosphere. All of the other elements are derived from the soil except in the case of peas, beans, clovers and other legumes which secure most of their nitrogen from the air.
The mineral elements are not needed in large amounts but well-balanced plant growth is strictly dependent upon their presence in available form. Of these elements, those most likely to be deficient either in total amount or in availability are nitrogen, phosphorus, potassium and calcium. It is entirely feasible and economical to apply concentrated chemical fertilizers containing the first three elements so that their lack will not constitute a limit to size of crops harvested. In many cases it is necessary to apply chemical fertilizers to get satisfactory yields, even where natural manures are available and can be applied as well.
In addition to supplying essential plant food, nitrogen, phosphorus and potassium perform specific functions in plant growth. The application of nitrogen in one of its readily available forms (e.g., nitrate of soda and sulphate of ammonia) will stimulate vegetative growth. If too much of this one element is applied, leaf and branch development may occur at the expense of the crop. Good results follow the use of nitrogen on grass sods and on leafy vegetables like spinach. On the other hand, corn, peas, beans and other seed-forming crops need to have the nitrogen balanced with phosphorus. Potatoes, in common with other tuber and root crops, will utilize plenty of potassium in the development of starch.
Sources of Plant Food.—Chemical fertilizers can be purchased at supply stores in ready mixed condition and of analyses that will meet general crop needs. A good formula for such a general purpose fertilizer is 4 to 5 per cent nitrogen, 7 to 9 per cent phosphoric acid and 7 to 10 per cent potash to the ton. It is known that such a mixture will supply the food needs of a large variety of plants in balanced amounts. Highly concentrated mixtures are now on the market providing double the amount of plant food in the example quoted, costing nearly twice as much but effecting a saving by cutting in half the material handled to get the same result. Care should be taken, in using these highly concentrated fertilizers, to avoid contact with tender roots. A mixture for general farm and garden purposes may contain the following ingredients:
| 100 | pounds nitrate of soda |
| 230 | pounds sulphate of ammonia |
| 250 | pounds animal tankage (7 per cent nitrogen) |
| 1,140 | pounds superphosphate (16 per cent phosphoric acid) |
| 280 | pounds muriate of potash (50 per cent potash) |
| 2,000 | pounds. |
This mixture will have a formula of 4-9-7 (4 per cent nitrogen, 9 per cent phosphoric acid and 7 per cent potassium). The individual who wishes to mix his own fertilizer may do so by purchasing the finely ground ingredients separately, and by means of a shovel, integrate them all into a mixture. Home mixing will not be found profitable where small amounts of fertilizer are used. Those who practice home mixing for the first time should realize that most combinations of ingredients will “set” or harden if not used immediately, necessitating the breaking up and pulverizing of the mass. When it is broken up after curing, no further difficulty should be experienced with “setting” if the mixture is kept in a dry place. The advantages of home mixing for the large user lie in lower cost per ton of plant food as a rule; confidence in the quality of the ingredients which he should purchase on the basis of guaranteed analysis; and the setting up of a mixture which study of his soil and the plant requirements has convinced him is best suited for his individual case.
Chemical Soil Analysis Not Helpful.—There is a mistaken notion that it is necessary to analyze soils chemically in order to fertilize them intelligently. Such an analysis of a reasonably fertile soil will show the presence of the essential elements of plant food, though perhaps not all in sufficient amounts, to produce ordinary crops for centuries to come. Only a small amount of the elements become available for root absorption each year and a chemical analysis will not bring out this most important factor—availability. The use of a few simple tests, mainly of a physical nature by a competent soils specialist, will prove of some assistance in the treatment of the soil. Such tests will show the presence of adequate amounts of humus, and indicate the acidity content. The soil texture will give some index of its crop adaptability and thereby serve as a basis for fertilizing treatment that will meet the needs of both soil and crop. The practical man will not expect any considerable aid from a highly technical and costly chemical analysis of his soil.