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adding a little more earth and haulm if necessary. All the urine, night-soil, soap-suds, soot, and all the domestic refuse, should be carefully added to the heap; the coal-ashes, unless sifted to a small powder, being kept by themselves. Sea-weed, when to be had, is an excellent ingredient in such composts ; and all brush-wood, furze, &c., chopped small. All animal remains, refuse of fish, hair, wool, rags, horn, bruised bones, and all refuse of the kind, should be carefully collected : animal remains are the richest in nitrogen. To a mixture of the above substances, half the bulk of manure when coarse, and about I or when more concentrated, should, when rotted together, be equal in value to the same bulk of rotted manure ; preventing the loss in the way manure is generally managed, and increasing the quantity in an immense degree. When the heap is near the field less dung may suffice to mix, but when it is to be carted far it should be rich, to save expense; the heap ferments more perfectly with a good proportion of hot manure. For such as root-weeds and seeds of weeds, there must be a hot fermentation to destroy them. When there is not much stable manure to mix with the compost, a mixture of wood-ashes, lime, and other substances yielding alkalies, is very beneficial, in causing the production of humic acid, forming humates with the alkalies in place of carbonic acid. Where much ammonia is in the compost, which will be the case wherever animal remains and excrements abound, lime is apt to cause the escape monia, by decomposing its carbonates and humates; and only so much should be used as will saturate the surplus of humic acid not taken up with ammonia. Sprengel recommends about to for some composts ; too much should, above all, be avoided. When sulphate of lime, sulphate of soda, and muriate of soda (salt), are cheap, they will be useful to add. The refuse of glue manufactories is rich in nitrogen. The refuse of woollen factories is rich in soap-suds, urine, &c. The refuse of tanners and skinners, the hair, skin, wool, and hoofs, is rich in nitrogen. The refuse of gas-works is well known as beneficial.
As regards the way in which carbon, forming the greatest proportion of any of the elements in plants, is obtained, there is still
very considerable difference of opinion. As we noticed in former essays, Professor Liebig is of opinion that most, if not all, is got by the leaves from the air; while Professor Schlieden, one of the most eminent physiologists of the day, in a criticism of the Chemistry and Physiology applied to Agriculture, of Liebig, (translated into the Gardener's Chronicle,) seems to be of a completely opposite opinion. The action of leaves on a growing branch confined in a vessel filled with air, in which it has been said the carbonic acid has, after a time, been found diminished and the oxygen accumulated, has always
been brought forward as proof of the fact that plants get most of their carbon from the air. These experiments, however, are difficult to manage so as to prevent error; and Schlieden asserts that, in the average of recorded experiments, it has been found that the enclosed air of the vessel has neither been altered in its quantitive nor qualitive relations. Dumas expresses himself hesitatingly on the point, and, though he leans to the supposition of the carbon being got principally from the air, and undoubtedly, he thinks, from carbonic acid, yet notices the great quantity of carbonic acid found by Boucherie to issue from the trunks of divided trees when felled in full sap, evidently derived, he says, from the roots. Professor Johnson seems to lean to the supposition that the greater part is from the air.
Professor Sprengel and Dr. Madden seem to be of opinion that the greater part of the carbon is got in the humic acid absorbed with the ammonia : the latter allows that very little of the carbon is got in the state of carbonic acid by the roots, while many are of opinion that what is got by the roots is principally in that form. I shall have an opportunity of entering more at length into this subject in the article “Vegetable Physiology.' While so much difference of opinion, however, prevails among learned men on the subject, practical men will do well to preserve and deposit in the soil the carbon, as well as the other portions of the manure. Fortunately, in the mixed manures generally applied, there are carbon, nitrogen, and inorganic matter; and in most soils, though not all, as asserted by some, there is generally a reserve of humus to assist when neglected. I doubt it would be found very difficult to grow plants luxuriantly in washed sand, with either ammonia or saline matter, or both, in an ordinary atmosphere. Such an experiment, however, might throw more light on the subject than most of those tried. Solutions of nitrates, sulphates, and phosphates of ammonia, potash, soda, lime, and magnesia, with silicates of potash and soda, and a little common salt, would furnish the nitrogen and inorganic substances wanted; but, I fear, would not produce luxuriance of growth without carbon.
On the subject of inorganic manures, the experiments recorded this season are manifold, and, as might have been expected, much at variance. Some applications, in certain circumstances, appearing to have had little effect; others to have done much good, and some to have done harm. The tables furnished of the quantities of these substances found in the different plants under cultivation, and the quantities furnished by the different kinds of manure, will, when properly regulated and corrected, show what are the wants of plants as to constituents, and how far the food deposited is capable of supplying these wants, a proper allowance being given for the portion washed away from soils; but there is still more to be done before correct data can be furnished. It is evident that saline substances are wanted for other purposes besides forming constituents. The quantity found in the young branches and leaves of trees is great, in comparison with what is found in the trunks; the quantity found in trees is comparatively much less than that found in annual crops; and the quantity in these is also much greater in the young succulent growing portions, than in the ripened tissue. These facts all
show that a liberal comparative supply is needed for the young growth, teaching the necessity of applying these and ammonia early to young seedling plants; and also teaching that these substances are necessary to assist in the transformations going on where life is most active, to fit the circulating juice for the purposes of the organs of assimilation, and that, where extra vigour is wished, a liberal supply of these substances must be furnished. The effects of this supply may be observed, wherever the burnt ashes of young unsaleable trees, or the clippings of hedges, have been applied to vegetable crops ; I have seen the effect often such as to defeat the end intended, by an over-luxuriance of stem and leaves to root crops.
I have seen very powerful effects, this season, follow the mixing of composts for pots with ashes of small branches burned and bruised to small pieces. At Roselle, the geranium leaves were like those of tussilago for size, of a deep green, and the vigour of growth so great as to injure the flowering. The excellent preparation of branches, straw, cabbage leaves, and other haulm, set fire to and kept at a smothered heat till charred, as pointed out in the November Number of the Magazine by Mr. Barnes of Bicton Gardens, will be very powerful. The greater the variety in the small branches, leaves, roots, &c., charred, the more likely are the ashes to answer general purposes. They contain the great variety of saline substances found in the most vital portions of the plants burned, which accounts for much of their action. Leaves will not grow, nor vital activity become active, till all the essentials of vital chemistry are provided; though the compost they are furnished with contains sufficient of carbon and ammonia. The ashes, also, act mechanically, as keeping the soil open by their elasticity, which is one of the principal benefits of farm-yard manure. They also absorb oxygen and ammonia from the soil and air; or, if the oxygen is from water, perhaps form ammonia from the nascent hydrogen, and absorb it, as most oxidising substances likely do. These absorbed gases will be given off to the roots. Roots are always exceedingly fond of running round such porous substances, and are found to increase
and multiply and get matted around them, which of itself must greatly assist. Whether the roots are impatient of too much moisture, or attracted by the gases absorbed as they cling round those charred pieces of wood, and of clay as in pieces of pot and brick, or whether opposite states of electricity may affect, it might be difficult to say. It is likely, however, that the absence of undue moisture, and the presence of a proper quantity of gases, form the principal cause. I have seen them cling round large pieces of porous bones with avidity, while they refused to enter the powdered small pieces of bones, where, perhaps, there was too great an abundance of food, the ends of the spongioles appearing diseased and swoln. The carbon of the ashes is also undoubtedly given off as the pieces begin to dissolve. I have seen such powder to increase greatly to appearance the growth of hyacinths in water, as compared with those in pure water; and the saline substances and carbon were likely to afford most of the benefit there.
To enable us to arrive at correct data, plants should be analysed in the various stages of their existence. The comparative analyses of plants must vary according to the age of the plant experimented on; according to the part of the plant examined also, if in portions ; perhaps, also, according to the liberality of the supply furnished to the roots. What is to be allowed for constituents, and what for assistants, and what perhaps deducted for superfluity, may be very difficult to solve, and may require many analyses of scientific men, and much judicious observation of practical men, before arriving at correct principles. Superfluity is undoubtedly prejudicial; and it has been frequently proved by experience, that plants will at times absorb both more water and more food in the water than are necessary, or than the leaves can elaborate, so as to enable the organs to assimilate. As the quantity of food absorbed depends partly on the quantity of water absorbed, excess in some seasons and some soils may more readily occur than in others. In seasons when little light is present, less water is, however, absorbed, though the season should be more wet and the ground more moist; and, to a certain extent, the one is a corrective of the other: yet confusion may arise from the confliction of causes, and may bafile and retard the efforts at establishing rules ; though, if we are cautious of deceiving ourselves and others with preconceived notions, and do not attempt to make practice bend to theory, it will undoubtedly in the end conduct us to the right path.
In endeavouring to ascertain from practice the necessity for these substances, by the effects produced by their application, the recorded effects of experiments are much at variance. Nitrate of soda has been found to have very different effects in different situations. This has been ascribed to the places in which it failed being near the sea coast; and, the lands abounding in salt (muriate of soda or chloride of sodium), they had therefore no need, it is said, for nitrate of soda, and hence the want of effect. At Roselle, which is so near the sea as to entitle it to the benefit of a saline atmosphere, and where common salt was found to produce no effect which might be ascribed to that cause, nitrate of soda was found to produce a powerful one. Yet even here it was found by the gardener that a small quantity killed the stool plants of sea-kale, while, at the Society's Experimental Gardens, it has been given in doses of 1 lb. to the plant with good effect. The nitric acid of the nitrate when absorbed must have a different effect from the muriatic acid or chlorine of the other. The latter are seldom found as constituents in plants, and little is known of their beneficial action; while nitric acid has been found by Braconnot to produce fibre from starch, and, if confirmed by further experience, may be found in this way to assist in performing an important part in the vegetable economy. It is also said to assist in the formation of oxalic acid, which last is thought to abound more in plants than analysis points out; the oxalate of potash being changed into a carbonate in extracting it. Like ammonia, nitric acid probably assists also, by the nitrogen it contains acting as a stimulus to growth: probably ammonia is formed from it, as it is generally found to give
ise to a dark green colour, denoting the alkaline state of he chromule, an appearance which generally betokens vigour of growth, but is sometimes found to appear without this increase. When a sufficient dose of manure has been given before the dressing of nitrates, they have been often found to produce no additional effect. At Caprington this season, a lot of potatoes had been manured at the rate of about fifty cubic yards of well rotted manure (about thirty tons), and the crop produced was about twenty tons per acre, the manure and working of the land being excellent : but some drills, dressed with the usual quantities of nitrate of soda, sulphate of soda, and urate containing a great deal of ammonia, had no perceptible increase; apparently from the large quantity of ammonia supplied by the manure to a crop not carrying off much nitrogen, the substances containing it had no effect. Some nitrate of soda and sulphate of soda, sprinkled on a crop of vetches in an adjoining field, caused a great increase of produce, showing that there was nothing naturally in the soil against their acting. The many causes noticed in the commencement of this essay may have occasioned different results, and may not have been observed. Sometimes the substances lie over year in cold soils and cold seasons before producing effect; and some may have been applied unwittingly to pieces of fields which were