WHAT IS SOIL ?
Soil is not dead matter. It is full of living bacteria which need air and moisture in order to perform their duties. Air and moisture in thedepend as much on its texture as on any chemical additions that can be made, and the improvement of soil texture is the first step in cultivation.
Soils are composed of varying proportions of sand, clay, chalk and gravel, together with humus, or decaying animal and. According to which of these ingredients predominates, soils are called by different names.
Sand consists of grains of quartz or other rocks, mainly silica, together with mineral impurities, some of which are possibly plant foods. Sandy soils are light soils.
Clay consists of the same material but ground to a finer powder and held together with a sticky material which is actually a compound of silica, alumina, and water. Stiff, or heavy soil, is soil which contains a very large proportion of clay.
Peat is a soil composed almost entirely of old vegetable matter. It is usually sour, that is to say it is deficient in lime, but when dressed with lime is often extremely fertile. Certain plants have adapted themselves to the conditions of peat soil, and will not grow in ordinary fertile garden soil where lime is present. The peat which is recommended for use in the cultivation of Orchids, and many other greenhouse plants, is the surface soil of heathland, and usually somewhat greyish in colour; it is not the peat which is dug out of marshy districts in Ireland for fuel.
Marl is a soil that contains carbonate of lime. Clayey marls are extremely fertile.
Humus is a name given to any decaying vegetable or animal matter in the soil, such as the decaying roots and leaves of former crops or stable manure.
Soil is usually referred to by gardeners as either light or heavy. Light soil is loose and sandy. A spade will go into it quite easily, and as each spadeful is lifted it will be found that the work is less arduous than on heavy soil. Light soil is not usually so fertile as heavy soil. Heavy soil is mainly clay, that is to say, it is composed of finer particles than light sandy soil. These fine particles adhere together, and hold more moisture than do the coarser particles. Heavy soil is much more tiring to the gardener. This is a case of “what you gain on the swings you lose on the roundabouts,” for what you may gain in easy management, you may easily lose in the lack of fertility of light soil.
All soil, heavy or light, must be brought into good condition by some improvement of the natural texture. This improvement is brought about in Nature’s domain by the falling of leaves, and the decay of plant tops, both of which add humus to the surface soil. In the garden, humus can be added in much the same way, that is by working into the soil all the available dead plant tops and decayed leaves, and digging in stable manure. The effect of adding humus in this way is to make light soil moister, and to make heavy soil lighter in texture and more porous, so that air penetrates to the plant roots. The treatment of both kinds of soil is therefore somewhat similar, the only difference being that the manure added to heavy soil should preferably be of a coarse, strawy nature, whereas the manure added to light soil should be heavier. Cow and pig manure are ideal for sandy gardens.
Digging of all kinds is done mainly in the winter months. The summer cultivation of soil consists of keeping the top spit in a light friable condition. For this a hoe is used. Many novices think that the use of the hoe is chiefly to destroy, but this is only half of the work that it is intended to do. It has been found by frequent experiments that soil which is kept hoed on the surface, so that it never cakes and cracks, is several degrees warmer in winter, and considerably moister in summer than unhoed soil. Hoeing therefore takes the place of watering, and is actually far better for the plants. The artificial application of water, particularly water from a cold tap, is not desirable at any season if it can be avoided.
The fertility of any soil depends not only on the amount of plant food in the soil but on the plant food which is available to the roots. Plant food can only be taken up by roots in the form of a solution, and insoluble plant food in the soil is, therefore, useless. That is why the vendors of fertilizers are required to state the amount of soluble food of each kind there is in their product.
The chief plant foods are phosphates, nitrogen and potash, and these three are often referred to as the “Golden Tripod.” They are essential for every kind of plant, and each has a special function. It is worthwhile for the amateur gardener to make himself acquainted with the effect of each of these plant foods on vegetable life, because, once understood, the vexed question of plant feeding becomes both more interesting and more profitable.
The other essential plant foods are present in sufficient quantities in most soils. They include water, sulphates, oxygen, iron, magnesia, soda, chlorides, and silica.
Of the three plant foods Nitrogen is the leaf-forming food. It makes a plant larger, and encourages quick development of leaves and stems. Applied after the flowers form it makes the individual flowers larger and finer, but it has to be used with care in the flower gardens. If it is applied too heavily to flowers of any kind, the effect is to make the plant larger and leafier, and possibly to delay flowering, which may mean that the flowers do not appear until after the frosts arrive.
Phosphates are the plant foods which produce flowers and fruit. They can therefore be applied freely in the flower garden and the orchard, and they are also useful in parts of the vegetable garden, such as, for instance, on Cauliflowers, Peas and Beans. But they are undesirable amongst such crops as Cabbages, which would be encouraged by an excess of phosphates to go early to seed.
The third plant food, potash, is a kind of tonic. It is essential to the health of the plant, and assists in fighting diseases. In fact, it is often better to apply potash to plants suffering from fungus troubles than to attempt to deal with them by the application of fungicides. These three plant foods are, however, useless in most cases without the presence of lime in the soil.
Lime is essential to all soils, except where a certain group of plants are grown called Calcifuges. Or lime-haters, of which the commonest representative is the. The amount of lime present in the soil should be at least one part in two hundred. Elaborate tests are available for estimating the amount of lime in any garden soil, but a simple method which the novice can undertake by himself is to take samples of soil from different parts of the garden. Mix them together, and put a little in a tumbler. Add to this about a tablespoonful of hydrochloric acid or muriatic acid. If the liquid bubbles freely, the soil contains a sufficient amount of lime for garden purposes. If it does not, a more or less liberal dressing of lime in some form is required.
The best time to apply lime is in the winter and in the form of slaked lime which is a fine powder. It is best to spread it evenly over the surface of the soil, where it can be left to be washed in by rains. It is not advisable to use lime amongst plants during the growing season, or allow it to lie on plant foliage. For this reason, it is better to use a fine powder, which can be dusted on to the soil surface, without harming the leaves. Also it is best to apply it during the winter months. Whenever a vacant plot has been dug deeply, lime should be applied at once over surface.
Chalk is a form of lime. It is quite as effective as a fertilizer, and useful on light sandy soils, but it does not break up heavy soil in the way that slaked lime does, nor does it assist in destroying pests in the soil. It can be applied to light soil at the rate of 2-3 oz. per square yard, but it should be broken up fairly small, and mixed into the top spit of soil.
Gas Lime is cheap and useful, but it contains a proportion of poisonous compounds of sulphur, and plants must not, therefore, be grown in the soil for some months after its application. It is used sometimes as an insecticide, but a good commercial soil fumigant would probably be better. From 2-4 oz. per square yard is sufficient for any purpose.