There is another mode of ridging, when the land has had one or two ploughings, in order to expose it to the frost in winter, and to mellow it. The operation is somewhat similar to ribbing, but after the first slice is turned over, another is added, as deep as the plough can be made to go, so as not to bring up the subsoil ; by this means the whole surface is laid in high ridges and deep furrows ; and when this ploughing is reversed, in spring, the soil which has been exposed to the frost and wind is mixed with the rest, and tends greatly to mellow it. This is an excellent preparation for turnips, if the land has been well cleaned. The manure, being distributed in the deep furrows, is covered by the plough right and left, or at one operation by a plough with a turn-furrow on each side, which divides the ridge and lays half of it in each contiguous furrow. This plough is usually called a double mould-board plough, and is extremely useful in many operations of husbandry.
In order to Lave hands and expedite the tillage of the land, ploughs have been contrived which make two or more furrows at once. When they are well constructed, they are very useful in light soils. If it is not recriired to go deep, and two horses can draw a double plough, there is a decided saving of power ; but if it requires four horses, nothing is gained. The double ploughs are therefore not much in use. But there are instruments which cultivate the earth, stirring and pulverising it much more speedily than the plough. Some of these will stir the ground to the depth of seven or eight inches, going over a width of five or six feet at once. Such an instrument is preferable to the plough, after the ground has already had a certain degree of stirring, and is become mellow and crumbling; but to break up pasture or clover-lea, there is nothing so efficacious as the plough, which cuts regular slices and lays them over, so that all the grass shall rot, and the roots, being exposed to the air, shall decay, and thus furnish food for other crops.
The instruments which have been invented to save the time and !abedr required by repeated ploughings are very numerous. Some of the most useful have been noticed before. [ARABLE LAND.] New ones are daily invented, and some are supported by wheels, which render them both lighter and more convenient. They are easily raised out of the ground, when not intended to work, and the depth to which they are lot down is more easily regulated.
Deep ploughing is generally acknowledged to accord with the best husbandry, where the subsoil is dry naturally, or has been artificially drained; but seine inconvenience may arise from bringing a barren subsoil to the surface, in trench-ploughing by two ploughs following each other in the same furrow. It has therefore been suggested to take off the turn-furrow from the plough which follows the first, so as to stir the subsoil without bringing it to the surface. [ARABLE LAND.] This idea has been improved upon by constructing a subsoil-plough of great strength, which will go very deep into the ground and stir the subsoil a foot or more below the bottom of the usual furrow. Mr.
Smith of Deanstone has invented one made entirely of iron, and Sir E. Stracey has constructed another with a small wheel in front very strongly put together, although the beam is of wood. Mr. Read, of Regent Street, London, has since manufactured another wholly of iron ; and, in its turn, this has been greatly improved by the Marquess of Tweeddale, and is made by Mr. Slight of Edinburgh. This plough requires four horses in the most favourable soils, and six in tenacious clays, to keep tip with the common plough, which always should precede it. Sometimes however the subsoil-plough may be used alone, where the surface is already mellow and crumbling.
Many different ploughs have been invented for the purpose of saving labour in draining land. As they all cut out a slice from the bottom of a furrow and raise it up to the surface of the ground, they are of little use in crumbling soils, and in the most tenacious require the assistance of much manual labour to complete the work. They act on the principle of the carpenter's tool by which a groove is formed in the edge of planks or deals, when they are intended to be joined closely as in a floor. This instrument is also called a plough ; but the uniform tenacity of the wood allows a narrow chisel to cut an even regular groove. In the draining-plough the two sides of the drain are to be cut obliquely downwards and the bottom scooped out evenly. Tho plough requires to be often adjusted, and the deep furrows to be kept cleared from loose earth by means of spades and scoops. In this way, drains may be made from 15 to 18 inches deep, in which loose stones or tiles may be laid to form a channel for the water. The expense is much less than when the drains are made with the spade.
When grass-land lies low and wet on a very tenacious subsoil, a plough is sometimes used which'consiets of a cylinder of iron pointed at one end, and connected with a strong beam by a thick plate, of iron which is sharp on the sidle nearest the point of the cylinder, and acts as a coulter. This instrument is forcibly drawn horizontally through the stiff subsoil at a depth of 18 inches to 3 or 4 feet, so as to leave a round channel like a pipe where the cylinder has passed. This has been called a mole-plough, the passage made by it under ground resembling the workings of a mole. It Is most effectively drawn by steam power, but though easy and expeditious, it is only as a means of temporarily draining land that it can be approved.
Various ploughs have been constructed with the intention of diminishing the draught, or improving the form of the turn-furrow ; but it may suffice to name as the most distinguished manufacturers of the present day—Messrs. Ransoms of Ipswich ; Messrs. Howard of Bedford, and Messrs. Hornsby of Grantham. In the application of steam to the impulsion of the plough, the effect sought to be produced is the same, the difference is in the power, and various patents have been obtained for steamplouglie.