Another important bearing tillage has on plant-growth may here be discussed. A problem of considerable difficulty is presented in the question, How many individual plants will a certain piece of soil support in a healthy way? For as plants require room, it is imperative that they be not too closely crowded together.
The question resolves itself pretty much into one of quality against quantity.
Experiments on this subject have shown that a certain area of soil is only able to support the healthy growth of a certain number of plants. If the limit be exceeded, the result is imperfect development.
Number of Plants on certain Area increased by Tillage.
It is obvious, however, that the more thoroughly tilled a soil is, the greater will be the number of plants it will be possible to grow on it. The roots, instead of being forced to spread themselves along the surface-soil, and thus take up a large amount of room, will find no difficulty in striking downwards. Two or three plants may thus be enabled to grow in a thoroughly tilled soil in the same space as only one could before tillage.
American and English Farming.
The above considerations throw considerable light on what seems to many farmers a strange anomaly—viz., the fact that the return of farm produce per acre on American farms is, as a rule, very much less than that from our own impoverished soils in this country. To many, at first sight, this seems to be in direct contradiction to our common belief, and to point to the conclusion that the virgin soils of America are, after all, actually inferior in fertility to the soils of Britain.
It is not, however, necessary to draw this conclusion, as the facts of the case admit of another explanation. The inferior returns obtained from American farms are due, not to the fact that the American soil is less fertile than the British—for this is not true—but to the fact that it is less intensively cultivated.
In America land is cheap and labour is dear; it is consequently found to be more economical to cultivate a large tract of land less thoroughly than a small area more thoroughly. In Britain the reverse is the case, labour being cheap and land being dear. It is thus necessary to make the land go as far as possible, and produce as heavy a crop as it is possible to produce. There can be little doubt, that were American farming to be carried on as intensively as is British farming, the present yield would be at least probably doubled.
We have now to consider the second class of properties which influence the fertility of a soil. These are chemical.