We come now to the use of bones as a manure. Raw bones contain perhaps half their weight of phosphate of lime ; when burnt they con tain perhaps 60 or 65 per cent, of phosphate of lime. It is chiefly for this phosphate that the bone manure is valuable, and as in addition to the greater quantities of phosphate which burnt bones contain, they are also superior as regards the facility with which they can be decomposed, burnt bones are more valuable agriculturally than raw ones. This phosphate exists in the mineral world both as fossils and simply in the mineral form ; some of the fossils contain half their weight of phosphate of lime ; and apatite, a mineral phosphate imported from Norway and America, contains upwards of 90 per cent. of phosphate of lime. It is, however, in its natural state almost valueless as a manure, owing to its insolubility ; and as the agricultural value of bones can be greatly increased by increasing their solubility, so whatever value this mineral phosphate possesses is conferred upon it by the same process.
This process consists in the adoption of means which shall have the effect of reducing the material to a fine state of division. When the phosphate of lime is acted on by sulphuric acid one half the lime is taken forms it by the acid, and so sulphate of lime or gypsum is pro duced, the other half of the lime in combination with all the phos phoric acid forms what is called super-phosphate, which is characterised by its solubility in water ; and although when it becomes mixed with the earth when put ou the land, this extra quantity of acid becomes neutralised by the lime or the alumina, of the soil, yet having been once decomposed the bone earth retains so exceedingly finely divided a state that rain is able to act upon it as a solvent much more power fully. The reason why bone-dust is more powerful as a manure than the original bones is, that its finer division gives a larger surface for rain water to act upon, and wash off a portion of its substance as food for plants. Ground and fermented bones are thus more immediate in their action. For further remarks on the use of bones and guano we 'refer to articles on those subjects. It is to them that we mainly look in this country for the means of supplementing the natural supply of manure on the farm.
It is not worth while going into any detail regarding the particular fitness of other special manures. In practice no reader is likely to go into the manure market for sulphate of magnesia and soda, nor even for silicates of potash and of soda; though these are said to be directly useful in strengthening straw. If the farmer can get a supply of guano, bone dust, superphosphate, and nitrate of soda, to supplement farmyard dung, he is not likely to go further.
As to the value of special mixtures of different salts on manure, certainly the fancy for that kind of thing ran wild some years ago, but the relative values of manures are becoming now better under stood. It is, however, right that we should say a word on soot as a manure. It is used everywhere with good effect in virtue of the gypsum which it contains, and in virtue of the small quantity of ammoniacal salt which it retains as driven off from the coal. Thirty bushels per acre are a common dressing for grass; and for potatoes it has been long known as a useful manure.
Leaving now the subject of auxiliary manures—which has latterly become one of the most important in the whole range of English agriculture—we recur once more in conclusion to the ordinary farm practice connected with the annual replenishment of the soil. Farm buildings should be so made as to remove all the water which falls upon the roofs, that it may not dilute the manure made in the yards. Their yards if any are open should be small and partly covered.
Arrangements for feeding in boxes where all the excrement is absorbed by the litter are to be preferred ; and. where yard-manure is made, or stall-fed cattle have to be daily cleaned out, the manure thus daily made should be daily removed made on Mr. Lawrence's plan, to which reference has already been made.
One word further may be allowed on the practice of folding sheep on land, and of top dressing clover and grass lands; the policy of that practice has been remarkably justified by the researches of Dr. Volcker, to which allusion has been made. Hitherto the wastefulness of top dressing has been admitted universally, and the practice has been regarded as one of the unfortunate circumstances connected with the plant so treated, which could not be avoided. Both top dressing and folding, however, which latter has all along been distinguished by the fertility It conferred, may be now regarded as practices which, if rightly performed, are not more wasteful than other modes of applying manure. It is becoming more and more the practice In England to apply the bulk of the farnainanure in this way. Clover, either immediately after the barley harvest, or during that autumn. receives a dressing of 10 to 15 tons of farm-yard dung, which as it has been made during the previous spring, is generally in a very well rotted state ; or the tame clover receives a heavy dreaming in the subsequent autumn, pre vious to being ploughed up for wheat.. The former is considered the best plan, at least as regards that portion of the clover which is to be mown In the following year. The turnip crop is thus being left more and more dependent on the use of artificial manure—a half-dressing of dung and a good dreseing of superphosphate of lime is found equal in effect to the beat whole dreaming of clung which under other manage ment the farm could afford.
One word on the practice of folding sheep on land in the case of light soils. It will no doubt be a permanent practice. Probably a larger portion however of the green crop break is being harvested and carried home to yards, for fatting stock to help convert the straw into dung, said to help, along with the consumption of clover, hay, and cake and, corn, to make much better dung than has hitherto in general been made. Probably on a light-land farm in Norfolk, one-third of the turnip-crop will be carried home, leaving two-thirds on the land for sheep. On the best managed lands there, every sheep will consume 1 cwt. of cake or corn, in addition to the 12th part of an acre of swedes, and if in doing that it increases 10 or 12 pounds a quarter, as it probably may, it will do little more than simply return in its excre ments all the green food which it has consumed. That turnip crop had built up its bulky structure at the expense of the deeper as well as of the shallower soil (for we have traced the roots of turnips 4 feet down wards), and largely also out of the material which it has gathered from the air ; and by means of the sheep this largo quantity of plant food, gathered from subsoil and from air, is all accumulated in the upper soil, greatly of course to its advantage, and greatly to the advantage of the subsequent wheat crop, and of such plants as, like it, may be more exclusively dependent than the turnip is upon the material which the surface soil contains. The material thus lodged upon the soil is in a form in which it is more liable to putrefaction and waste than it was: but air washes these fugitive ingredients into the land, and the plough soon covers all up ; and when the mechanical structure of the land is such as to benefit by the treading of the animals thus fed, there is no operation in the whole range of farm practice which at once adds such an increased fertility to the soil.