IRRIGATION. In China and in India, as well as in Egypt, ingenious modes of watering lands have been adopted from the most re mote ages. No expense has been thought too great to secure a supply of water, and to dis tribute it in the most advantageous manner.
The whole art of irrigation may be deduced from two simple rules : first, to give a suffi cient supply of water during all the time the plants are growing ; and, secondly, never to allow it to accumulate so long as to stagnate. The supply of water must come from natural lakes and rivers, or from artificial wells and ponds, in which it is collected in sufficient quantity to disperse it over a certain surface. As the water must flow over the land, or in channels through it, the supplymust be above the level of the land to be irrigated. But there must also be a ready exit for the water, and therefore the land must not be so low as the natural level of the common receptacle of the waters, whether it be a lake or the sea, to which they run.
When there is a considerable fall and a sufficient supply of water, a series of channels may be made, so situated below each other, that the second collects the water which the first has supplied, and in its turn becomes a feeder to irrigate the lower parts of the decli vity : a third channel receives the water and distributes it lower down, until the last pours it into the river. This is called catth-work,
because the water is caught from one channel to another. When the surface to be irrigated is very flat and nearly level, it is necessary to form artificial slopes for the water to run over; the whole of the ground is laid in broad beds, undulating. like the waves of the sea; and the water, carried along the ridge of each bed, is allowed to flow down the slopes. When it is intended to form a water-meadow on a surface which is nearly level, the whole of the land is laid in beds about 20 or 30 feet )vide, the mid dle or crown of these beds being on a level with the main feeders, and the bottoms or drains on a level with the lower exit of the water, or a little above it. Grass-seed being sown over these beds, the water may be let on for a very short time, to make them spring. As soon as the grass is two or three inches above ground, a regular flooding may be given and in a very short time the sward will be complete. Instead of sowing seed, tufts of grass cut from old sward may be spread over the newly formed beds, and they will soon cover the groUnd.
The rules for adjusting the time and mode of irrigation to the growth of the plants are among the studies of practical agriculture.