336 SCIENCE OF AGRICULTURE. Part II. 



obtained, which had a brown colour, and tasted like mucilage. From 400 grains of 

 wheaten-straw were obtained five grains of a similar substance. There can be no doubt 

 that the straw of different crops, immediately ploughed into the ground, affords nourish- 

 ment to plants; but there is an objection to this method of using straw, from the 

 difficulty of burying long straw, and from its rendering the husbandry foul. When straw 

 is made to ferment, it becomes a more manageable manure ; but there is likewise, on the 

 whole, a great loss of nutritive matter. More manure is perhaps supplied for a single 

 crop ; but the land is less improved than it would be, supposing the whole of the 

 vegetable matter could be finely divided and mixed with the soil. It is usual to carry 

 straw that can be employed for no other purpose to the dunghill, to ferment and 

 decompose ; but it is worth experiment, whether it may not be more economically 

 applied when chopped small by a proper machine, and kept dry till it be ploughed-in for 

 the use of a crop. In this case, though it would decompose much more slowly, and 

 produce less effect at first, yet its influence would be much more lasting." 



2239. Sir Humphrey Davy's opinion as to the application of farm-yard manure is in several points 

 directly at variance with the experience of farmers. There may often be an error in allowing such 

 manure to reach too high a degree of fermentation and putrefaction before it is applied to the soil ; but in 

 no case has it ever been found advantageous to apply it before the process of fermentation has actually 

 begun. As to its fermenting after being spread upon the soil and ploughed down, it must be evident, 

 upon a little reflection, either that no sensible fermentation would talce place at all, unless the quantity 

 yvere very large, or that its gases would be speedily exhaled through the loose covering of earth, and lost 

 in the atmosphere. Mr, Coke of Holkham's practice, which has been so often referred to in support of 

 the use of longer fresh dung, is in fact not different from that of the best turnip-land farmers of Scotland. 

 Mr. Blaikie, his steward, a native of Roxburghshire, prepares his farm-yard manure for turnips in what 

 are called pyes or camps in much the same way, and the dung undergoes much the same degree of 

 fermentation in them as is done with the square or oblong dunghills of the turnip counties of Scot- 

 land (C.) 



2240. Mere woody fhre seems to be the only vegetable matter that requires fermenta- 

 tion to render it nutritive to plants. Tanners' spent bark is a substance of this kind. 

 A. Young, in his excellent Essay on Manure, states " that spent bark seemed rather to 

 injure than assist vegetation ;" which he attributes to the astringent matter that it contains. 

 But, in fact, it is freed from all soluble substances, by the operation of water in the tan- 

 pit ; and, if injurious to vegetation, the effect is probably owing to its agency upon water, 

 or to its mechanical effects. It is a substance very absorbent and retentive of moisture, 

 and yet not penetrable by the roots of plants. 



2241. Inert peaty matter is a substance of the same kind. It remains for years ex- 

 posed to water and air without undergoing change, and in this state yields little or no 

 nourishment to plants. Woody fibre will not ferment, unless some substances are mixed 

 with it which act the same part as the mucilage, sugar, and extractive or albuminous 

 inatters with which it is usually kssociated in herbs and succulent vegetables. Lord 

 Meadowbank has judiciously recommended a mixture of common farm-yard dung for 

 the purpose of bringing peat into fermentation : any putrescible or fermentable substance 

 will answer the end ; and the more a substance heats, and the more readily it ferments, 

 the better will it be fitted for the purpose. Lord Meadowbank states, that one part of 

 dung is sufficient to bring three or four parts of peat into a state in which it is fitted to 

 be applied to land ; but, of course, the quantity must vary according to the nature of the 

 dung and of the peat. In cases in which some living vegetables are mixed with the 

 peat, the fermentation will be more readily effected. 



2242. Tanners' spent bark, shavings of wood, and saw-dust, will probably require as 

 much dung to bring them into fermentation as the worst kind of peat. Woody fibre 

 may be likewise prepared, so as to become a manure, by the action of lime. It is evident, 

 from the analysis of woody fibre by Guy Lussac and Th^nard (which shows that it 

 consists principally of the elements of water and carbon, the carbon being in larger 

 quantities than in the other vegetable compounds), that any process which tends to abstract 

 carbonaceous matter from it must bring it nearer in composition to the soluble principles ; 

 and this is done in fermentation by the absorption of oxygen and production of carbonic 

 acid ; and a similar effect, it will be shown, is produced by lime. 



2243. JVood-ashes, imperfectly formed, that is, wood-ashes containing much charcoal, 

 are said to have been used with success as a manure. A part of their effects may be 

 owing to the slow and gradual consumption of the charcoal, which seems capable, under 

 other circumstances than those of actual combustion, of absorbing oxygen, so as to become 

 carbonic acid. In April 1 803, some well burnt charcoal was enclosed by Sir H. Davy 

 in a tube, which was half filled with pure water and half with common air, and then 

 hermetically sealed. The tube was opened under pure water, in the spring of 1 804, at 

 a time when the atmospheric temperature and pressure were nearly the same as at the 

 commencement of the experiment. Some water rushed in ; and, on analysing a little 

 air, which was expelled from the tube by the agency of heat, it was found to contain 

 only seven per cent of oxygen. The water in the tube, when mixed with lime-water, 

 produced a copious precipitate ; so that carbonic acid had evidently been formed and 

 dissolved by the water. ' 



