Lands are laid fallow either during the summer, or during the winter, according to the nature of the soil, and the judgment of the cultivator. It is not our intention to enter into the dispute relative to the necessity or inutility of summer fallows; as very able arguments have been alledged as well for, as against it, by skilful agriculturists. Both summer and winter fallows, however, are occasionally useful on different $oils.
The advantages to be derived from fallowing are : 1. By repeatedly turning soils over, much carbonic acid, or fixed air, is produced in a fluid state, which remains united with the vegetable recrements, or with volatile aikali, or calcareous earth. 2. The parts of the soil become better incorporated, and thus reciprocally ameliorated ; so that they may afford more uniform nourishment to the roots of plants. 3. The pulverized soil is more easily penetrable, and thus exposes a greater surface of its cavities to the vegetable absorbents. 4. All unprofitable plants, or weeds, being thus eradicated, or continually ploughed under the soil, while yet young, a considerable proportion of vegetable nutriment will be reserved, and farther increased, by the saccharine and mu-cilaginous matter of the young Yegetables buried by the plough Lastly, some plants, during their herbaceous state, do not exhaust the ground on which they grow, before the seed-stems arise; as turnips, for instance, when pulled up, and carried away for the purpose of feeding cattle, or sheep, on other grounds. This benefit appears to arise from the soil being shaded by the thick foliage of those vegetables, and consequently ameliorated; for its nutritious properties cannot have suffered by evaporation so much, as if the land had been exposed to the scorching influence of the sun.
Dr. Darwin, when treating on this subject, justly observes, that, though a summer fallow may be of advantage to a poor soil, which has nothing to lose, yet it must be injurious to a rich one, which has nothing to gain.
A Fallow-cleansing a Machine was invented by a Mr. AaronOgdlx, a smith, at Ashton-under-Line, near Manchester. It consists of two large rollers, armed with iron spikes, to which the inventor prefixed an harrow so constructed, that it may be set to go to any depth in a furrow, without weighting} and will pulverize the soil, raise the roots, or weeds, to the surface, and at the same time not be obstructed by their accumulation, though it should raise as many weeds as would load a cart within the thort space of five yards. There are several other pieces of machinery belonging to this implement; but as they are intricate, we refer the reader to the 3d vol. of the work, entitled "Museum Rusticum et Com merciale," where its parts are minutely described, and illustrated with a plate. - The design of this machine is to clear fallowed land from,' from quick and all other weeds, in a better and more expeditious manner than is effected by manual labour ; and Mr. Ogden is of opinion, that two men, with three horses and his implement, may perform as much work as forty men in the ordinary way, beside saving one fallowing season ; an object of the utmost importance to the speculative farmer.