When digging, the soil should be broken up as finely as possible with the spade or fork, so as to leave no lumps, and all large stones should be thrown out.
Digging or plowing should never be attempted when the ground is frozen or when it is so wet that the soil sticks to the tools used.
After the soil has been turned over and broken up the rake should come into operation and the surface fined so as to fit it for seed-sowing.
V
FERTILIZERS
The most important elements that it is necessary to apply to the soil in the form of fertilizer are nitrogen, phosphorus, and potash.
Nitrogen greatly stimulates the production of leaves, and an excess of it applied to crops grown for their fruit or roots is undesirable. It is contained in all the animal manures, associated with other fertilizing elements, and in a practically pure state in nitrate of soda.
Phosphorus is a valuable and necessary fertilizer which has a great influence on the production of fruits and seeds. It is found in greater or less quantities in animal manures, and in bone meal. Phosphatic rock that has been treated with acid is another important source of phosphorus.
Potash. The rôle of potash in the soil is similar to that of phosphoric acid. It is considered to be a valuable fertilizer for all crops that are grown for their roots. It occurs in animal manures and in wood ashes. Muriate of potash and kainite contain potash in a more concentrated form, but are difficult to obtain at present.
All of these three elements must be present in the soil for the production of healthy crops.
It is generally conceded that the best all-round fertilizer for plants is decayed barn-yard or stable manure. It not only adds fertility to the soil, but by its decay it helps to make the mineral particles soluble and thus available as plant foods. As already indicated, it also improves the physical condition of the soil, making sandy soils more retentive of moisture, and rendering clay soils more porous. When applied in the spring it should be decayed or partly decayed, as in this condition it is immediately available for the use of the crop. If it is put on the ground in the fall, fresh manure may be used and plowed under. By the time that the planting season arrives it will be sufficiently decayed. If there is no objection on the score of appearances, stable manure, either fresh or decayed, may be applied in the form of a thin mulch (a layer on the surface of the ground) at any time when the plants are growing. The fertility is gradually washed down into the soil by rain, and a loose covering of this kind is of additional advantage in that it helps to prevent the loss of water from the soil by evaporation. This mulch must not be worked into the soil so that it comes in contact with the plant roots, but should be left on the surface until it is dug under the following fall or spring. Discretion must be exercised in its use. Root crops, that are already growing luxuriantly, such as beets or carrots, or crops that are grown for their fruit, such as beans and tomatoes, would probably be harmed by a surface dressing of this kind. Barn-yard manure is rich in nitrogen, which is a great stimulant of leaf growth. If it is applied too freely to the crops just mentioned it is likely to result in an excessive crop of leaves at the expense of roots or fruit.