The use of quick-lime in rendering inert vegetable fibres soluble, and hastening the decomposition of animal substances, is of the greatest importance in agriculture. Substances may be rendered highly enrich ing in a short time, which, without it, would have lain long dormant in the soil or the dung-heap. Its effects in this way will be more particularly noticed when we treat of composts.
Wherever there is peaty matter in the soil—which, owing to the tannin principle which it contains, is, by itself, perfectly incapable of putrefaction—lime is the true remedy. On the other hand, in a very stiff clay, chalk or lime will render it much more porous, and admit the influence of the atmosphere ; it will 'correct acidity, and assist the nutritious effects of animal and vegetable manures. Quick-lime spread on a soil abounding in vegetable matter will make it active by dissolving the half-decomposed fibres and converting them into a soluble mucilage : being extremely minutely divided by its property of attracting moisture rapidly, a very small quantity produces an immediate effect. Hence it is generally spread over fallows or clover-leys, which are preparing for wheat-sowing. If it were put on the land long before the seed is sown, it would have lost its chief and immediate power by attracting carbonic acid and returning to the etato of carbonate or ehalk,and all the expense of burning would be thrown away, except as far as it has thoroughly pulverised it. But frost does this with chalk spread before winter at a much cheaper rate ; and a good dressing with chalk will last in the soil, and its effects be preserved, many years after all the lime would have disappeared. It is therefore a matter of niere experiment and calculation whether it be more profitable to put ten wagvn-loads of chalk on an acre of stiff clay, or one or two' waggon-loads of quick lime. 1 f the soil bo very tenacious, the chalk will probably be the most profitable in the end as well as the cheapest; but for a few crops the lime may appear to have the advantage. Everything depends on situation, and the comparative facility with which lime and chalk can be procured.
On poor sands chalk will be found to produce a greater and more permanent improvement than the same value in lime, which, unless it be mixed with clay or vegetable substances, will not be of great use on such soils. When marl can be procured, or clay and chalk, these will
be the teat correctives for the porous nature of sand, whether mixed by nature or artificially. But marls are chiefly "amendments," and as such will be noticed separately.
It may however be mentioned here, that experience in the use of limo has varied exceedingly owing to two causes ; one of which is that limes vary exceedingly in their qualities. and the other, that crops vary exceedingly in their need of limo. The latter of these particularly points to the use of lima as being directly the food of plants, and thus more influential for one crop than another. On the former we may merely state that analyses of lime from quarries in different parts of the island, show that the quantity of lime present varies from 60 to nearly 100 per cent. And an even more valuable ingredient than lime in certain limestones, namely, phosphate of lime, certainly arida largely to the fertilising influence which certain limestones exhibit. Thus iu Connemara. Mr. Whitwell of Kendal has had various limestones analysed, with the following results : It is plain that differences of this kind must produce very great differences indeed in the fertilising, influence of the lime we apply. A limestone containing only 68 per cent. of lime, such as some of them near Dublin, will be of less value than a Durham limestone containing DI per cent. (just as 68 is less than 91)in respect merely of the effect of the caustic calcareous matters on the soil ; but if, apart from this mere carbonate there be present a phosphate in any quantity, an effect of an altogether different and valuable kind must follow its application. The mineral phosphate which, while in the masses of the rock, would be comparatively useless, 'auk, when broken down to powder as by burning and slaking the limestone rock, it becomes, be so laid open to the influence of the solvents of the rain and air, as to act upon the plants like a dressing of bones. Then again, consider the effect of a huge quantity of magnesia, which when caustic acts more slowly but snore persistently—and you cannot doubt that the composition of the limestone yeti employ must be looked to for much of the explana tion of the results of its application.