Although regarded as being almost entirely an agricultural operation, many market gardeners also adopt this method of breaking up their open land, and often even use the plough between fruit trees and bushes when space permits.

Ploughing itself requires a good deal of skill on the part of the workman. A good ploughman will not only adjust the implement in such a way as to place as little strain as possible upon his horses, but he will also perform more good work in a given time than an unskilled or slovenly worker.

In ploughing, the surface soil only is broken up to a depth of 6 in. or 8 in., the width of each furrow being about 10 in. on an average. The cost of ploughing an acre of ground is about 15s., but it may be more or less according to the nature of the soil. From 1 to 1 1/2 ac. can be ploughed in a day, and it is this facility for turning over the ground quickly that has made ploughing more popular than spade cultivation. When the ground is "subsoiled" a subsoil plough follows the other in the trench and moves the lower soil to a depth of 15 to 18 in. The cost of subsoiling 1 ac. of land would be about the same as for ploughing, thus making the total cost per acre for the two operations from 30s. to 40s. There are many kinds of ploughs now in use, but all have the same object in view, namely, to turn the soil up as well and as quickly as possible at the least expense.

One of the latest inventions is an electric plough, invented by Mr. E. O. Walker of Manchester. This is intended to supersede the steam plough, wherever electric power can be procured easily and cheaply. Electric wires overhead are used for a trolley as in tramcars, and the plough is hauled across the field from one side to another as in the case of steam ploughs. The same principles of shallow ploughing are adopted, but if electricity or steam could be harnessed in such a way as to turn the soil over to a depth of two or three feet, it would make a vast difference to the fertility of the soil in the course of a year or two.

Diagram showing Water (W) standing between Ridges in Land ploughed 6 in. deep.

Fig. 85. - Diagram showing Water (W) standing between Ridges in Land ploughed 6 in. deep.

The great disadvantage of ploughing is that the soil is not turned over to a great depth, and a hard pan is formed beneath the loosened layer. In some soils this pan is so hard that it is impossible for air or rain to enter the subsoil; and it is just as difficult, for the same reason, for the tender rootlets of the plant to extend their search for food. All the fertilizing advantages to be derived from the drying and warming action of the air, the solvent effects of the rain, and the penetrating power of the roots are thus rendered abortive, or at least greatly reduced. The diagram (fig. 85) shows how the water after a heavy rain remains on the surface between the ridges in ploughed land, until it is evaporated by the heat of the atmosphere and the wind. Under such circumstances the soil is cold and wet, and cannot be worked, while the beneficial bacteria cannot come into being in the soil until warmer and drier conditions prevail. The hard pan brought about by repeated ploughings has been recognized as such an evil by some American farmers, that they have taken the heroic measure of breaking the subsoil up by charges of dynamite.