the lighter soils that lime is applied; for then is not only lime applied, but alumina, to improve the texture of the soil. It is by means of this mixture that some of the greatest improvements on silicious sands that have taken place in Europe have been effected.

There are cases in which even calcareous matter is in excess in soils. This occurs especially in districts where the chalk formation exists. When the earthy stratum resting upon chalk is very thin, the chalky matter becomes mixed with it, and, being then in excess, forms a barren soil.

An obvious means of amending the composition of a soil of this kind, is by adding any of the other earths, whether silicious or aluminous. We need not here scruple to apply them because the clay is coarse or the sand silicious. We may add them in almost any form in which they can be conveniently procured; for the effect will be to improve the composition of the soil.

There is another case in which, in like manner, silicious and aluminous matter may be applied, directly, in almost any state in which it may be found. This is in the case of peat. Here the vegetable matter is in excess, and the addition, accordingly, of any other earths is an amendment of the composition of the soil.

We see, then, that the composition of soils may be improved by the addition of animal and vegetable matter, and also in many cases by the addition of the earths in which they may be deficient, and in an especial degree of lime, which we can always apply in the form of minute division best suited to improve the composition of the soil. This is the first of the means referred to of adding to the productive power of soils, and will be considered in detail under the head Manures, and other divisions of the management of the farm.

The second means referred to of increasing the

productive power of a soil, is altering its texture, depth, and properties, by tillage and other means.

The mere effect of that comminution of the parts of soil which it undergoes in the common operations of tillage, is seen to have a beneficial influence on the productive powers of the soil. Whether the soil imbibes from the atmosphere anything but aqueous vapour or not, it is known that the exposure of the matter of the soil to the atmosphere, and the comminuting of its parts by tillage, add permanently to its fertility. Thus we learn from experience the good effects of tilling lands well; soils once tilled are rendered, for the most part, more productive by the process. Peaty turf, if suffered to remain in its original state, may continue to produce nothing but heath and the most useless plants; but, if merely ploughed and exposed to the influ ence of the atmosphere, it will at once tend to produce grasses of a better kind and of greater variety; and, again, if a subsoil of coarse clay be exposed to the atmosphere for the first time, it is generally at the first very unproductive, and it is not until after long exposure to the air that it becomes productive. This is most remarkable in the case of clay marl, a substance, in itself, containing the materials of a fertile soil, but which is often barren until after pulverization and the influence of the, atmosphere.

It is, indeed, conformable to analogy, as well as to experience, that soils should be improved by pulverization and exposure to the atmosphere. In our examination of the constituent parts of soils, we have seen that their fertility is in a great degree indicated by the proportion of minutely divided earthy matter which they contain.

The effect of tillage, therefore, may be reasonably supposed to promote this division, both by the mechanical action of our instruments, and by exposing the particles of the earth to the action of the air. VOL. I.-G

Another object sometimes produced by tillage, and subservient to the amendment of the soil, is the deepening of the upper stratum.

The subsoil, it has been seen, is distinguished from the soil, so called, by its containing less vegetable and animal matter, and so being less suited to the nourishment of plants; and in many cases it is even found to be injurious to vegetation. It is generally important, however, that there be a good depth of soil, and thus it is often expedient, as a means of effecting a permanent improvement of the surface, to plough up and mix with it a portion of subsoil, even though that subsoil should in itself be infertile.

These, then, are the principal mechanical means by which we can improve the soil, and they will be considered in detail, under the various heads which relate to the operations of tillage.

Another means, indeed, of changing the composition of soils is incineration, commonly called paring and burning. This process will he described as connected with the operations of tillage, and may be considered as one of the mechanical means possessed by us of adding to the productiveness of the soil.

The third means referred to, of adding to the productive power of soils, is changing their relation with respect to moisture.

In warmer countries, the soil is comparatively little injured by an excess of water, and more frequently suffers from the insufficiency of it. In climates like that of Britain, however, the operation of conveying away the water which is in excess is an essential one, and, if neglected, the devised scheme of improvement may fail. The surplus water is either stagnant upon the surface, or penetrates below the surface. The freeing of cultivated land of water upon the surface gives rise for the formation of land into ridges, by which the water escapes

without stagnating upon the ground, or sinking into the subsoil below. This is an object necessarily connected with tillage, and will be described when the manner of cultivating land is treated of.

The freeing of the soil again from that superfluous water which is contained below the surface, forms a peculiar branch of agricultural improvement, and will be described under the head of Draining.

As draining is more required in colder countries, so irrigation, or the watering of land, is less required in those countries where the heat and evaporation are greater. Irrigation, however, is a curious and interesting branch of rural economy, derived by us from very ancient times. In this country it is chiefly employed in watering the lands in grass during the months of winter and spring.

The last of the means referred to, of adding to the productive power of soils, is by changing the relation with respect to temperature.

This means of adding to the productive power of soils is less within our control than any of the others. It is only by slow degrees that we can improve the climate of a country. It is chiefly by draining, and the raising of hedges and wood; all of these, accordingly, form important objects of rural economy, and will be partially treated of in this work.

The means, then, of adding to the productive powers of the soil, namely, supplying the organic and earthy substances which may be required; altering its texture, depth, and properties, by mechanical means, and changing its relation with respect to moisture, will all be treated of under the different divisions of our subject; and we shall begin with that which is most closely connected with the nature and property of soils, the nature and property of those substances which we apply to the soil under the name of manures.-Low's Elements of Practical Agriculture.

CHAPTER VI.

Supply of Food to Plants by Manure and Culture.

WITH regard to the food of plants derived from the atmosphere, the supply is pretty regular, at least in as far as the gases are concerned; for they are not found to vary materially in their proportions on any part of the surface of the globe; but the quantity of moisture contained in the atmosphere is continually varying, so that in the same season you have not always the same quantity, though in the course of the year the deficiency is perhaps made up. From the atmosphere, therefore, there is a regular supply of vegetable food kept up by nature for the support of vegetable life, independent of the aid of man: and if human aid were even wanted, it does not appear that it would be of much avail. But this is by no means the case with regard to soils; for if soils are less regular in their composition, they are at least more in the reach of human management. The supply of food may be increased by altering the mechanical or chymical constitution of soils; and by the addition of food in the form of manures. The mechanical constitution of soils may be altered by pulverization, consolidation, draining, and watering; their chymical properties by aeration and torrification; both mechanical and chymical properties, by the addition of earths and other substances; and manures, either liquid or solid, are supplied by irrigation and distribution of dungs and other nourishing matters, with or without their interment.

Soils in a state of culture, though consisting originally of the due proportion of ingredients, may yet