THE THEORY OF ‘NO DIGGING’
Some people who do not believe in digging claim to have obtained good results by simply using heavy organic mulches without incorporating them into the, but the usual practice is to work the material into the surface to a depth of 6 to 8 in. The nutrients in organic manures are of no direct use to plants until they have been broken down into simpler substances. For example, the protein which is a source of nitrogen in farmyard manure is of no use at all until it is converted into nitrates, when it can be taken up by the plants. And if there were no microbes in the soil, manure and organic fertilizers such as dried blood and bone meal would yield no nutrients at all.
LIVING SOIL ORGANISMS
The soil is teeming with hordes of small creatures belonging to both the animal and vegetable kingdoms. Vast numbers of earthworms, insects, protozoa and other small animals are at home in the soil, as well as tiny microscopic plants such as bacteria, fungi, algae and actinomycetes. These latter are generally called micro-organisms, and there may be billions of them in a small lump of soil, a fact which is difficult to believe without seeing them through a powerful micro-scope.
Not all soils contain the same kind and number of micro-organisms, but most rich garden soils contain numerous bacteria. Most of these microbes are beneficial. In fact, were it not for micro-organisms the earth might still be covered with rocks only, and would be without the greatest natural resource of all, the soil.
Of the many different organisms that break down organic remains, earthworms start the ball rolling by eating debris and partially decomposing it. It is thus reduced to a suitable condition for attack by the micro-organisms. During the processes of decay, the dead plant tissues are broken into simpler forms, which are then available for the growth of numerous kinds of plants.
In addition to the decomposition of inorganic and organic residues by micro-organisms, some special bacteria convert nitrogen from the air so that it is available for the growth of numerous kinds of plants. Some nitrogen-absorbing bacteria live on the roots of, beans and other legumes, and thus create the characteristic nodules which are so often seen when such plants are lifted from the soil. That is why it is best to bury the roots of peas and beans so as to conserve nitrogen in the soil.
Other kinds of bacteria convert ammonia into nitrates, which are then also available for plant growth. Sulphate of Ammonia, used as a fertilizer, depends upon this kind of bacteria for its action.
There are also the mycorrhizal fungi which live on the roots of many plants, from which they receive at least part of their food. In return they may act as water absorbers for their hosts, and may supply them with certain useful chemicals. But many organisms attack the roots of plants, causing damping-off diseases and various root rots.
Not all organisms live on decaying. Some are predatory, living on other soil organisms, so that the crowded community of micro-organisms in the soil is rather like a jungle. Many species prey upon others and the waste products of one become the food of others. Soils rich in also breed certain moulds and actinomycetes which reduce the numbers of fungi that produce , as well as breeding powerful antibiotic substances that have opened up new vistas in medicine. These all come from microbes.
Activity of Soil Organisms
The activity of micro-organisms varies with the season of the year, being greatest in the spring and autumn, and least in the summer and winter. Fortunately, the spring peak of activity coincides with the maximum growth of plants, and is probably one of the reasons why certain kinds of manures are most effective when applied in spring. Nutrients released by bacterial action are set free into the soil in the greatest amounts at the time they are most needed. So, when feeding crops, do not forget the microbes. There are so many below the ground, busily eating — and very efficient foragers they are too — that in an acre of land the weight of live-stock below the surface is as great as the weight of livestock feeding above the ground. The microbes have first call on any nutrients which may be applied; the green plants really get what is left over. In boggy areas, where the ground is waterlogged and often acid, bacteria do not thrive, and consequently plant remains are not properly decomposed. The operation of breaking down tissues is then taken over by fungi, which can tolerate greater acidity than the bacteria. This results in a slow accumulation of partially decayed vegetable matter that when compressed, forms peat.