MANURES. 



155 



deficient in phosphoric acid, and a general 

 manure is used, only the phosphoric acid in it 

 will be of any use, while the nitrogen and 

 potash it contains will yield no return, and the 

 nitrogen at least will always be liable to waste 

 by drainage. For the economical use of manures 

 considerable knowledge and discretion are re- 

 quired, in order to judge of the condition of the 

 soil and the requirements of the crop; for it 

 must be remembered that it is the constituent 

 of plant-food required which is present in the 

 soil in least proportion compared with the re- 

 quirements of the plant which controls the ex- 

 tent of the crop. If there is enough of this least- 

 plentiful constituent for producing a full crop, 

 all will be well; but if there is not sufficient, a 

 full crop cannot be obtained, even though other 

 ingredients of plant-food are present in very 

 large quantity. 



I. Organic Manures. 



In this class are included all substances of 

 vegetable and animal origin which have the 

 property of enriching the soil, or of supplying 

 it with substances required by plants for food. 

 All vegetable and animal substances used as 

 manure must undergo decomposition before 

 they can become the food of plants, for the 

 roots of these only absorb liquids and gases. 

 This change is generally effected to a certain 

 extent in the compost heap or dung clamp, 

 before they are applied to the soil; but in the 

 case of green manures, it takes place entirely in 

 the soil. 



Leaves. — These, when thoroughly decayed 

 and reduced to the state of mould, form a sort 

 of manure which, alone or mixed with soil or 

 other substances, is eminently suited for the 

 growth of most plants. Leaf-mould, as it is 

 called, is generally in great request for the 

 cultivation of pot plants. Autumn leaves are 

 necessarily comparatively poor in manurial con- 

 stituents, since these elements pass out from 

 the leaves into the body of the tree with the 

 approach of winter, there to be held in store 

 for next year's use. The best quality of autumn 

 leaves recently fallen from hardwood trees, 

 would contain in one ton, say, 6 lbs. of potash, 

 about 3 lbs. of phosphoric acid, and from 10 

 to 15 lbs. of nitrogen. 



Peat. — Bog or moor peat may be said to be 

 an accumulation of humus, produced by the 

 decay of plants that have been more or less 

 submerged; and it would then seem to be 

 derived from that which forms the first food 



of vegetation. But in the formation of peat 

 highly antiseptic properties have been imparted 

 which must be neutralized before growing 

 plants can avail themselves of the peaty 

 substance for nourishment. Much of this sub- 

 stance has been derived from the debris of 

 heath, which contains much of the tannin prin- 

 ciple; and there is some resin derived from the 

 fir wood, which had been very abundant, as the 

 trunks and roots of the fir tribe still remain to 

 testify, and so completely preserved that even 

 the small fibres can be drawn out entire. Not 

 only plants, but deer and other animals, have 

 been found in peat, which must have been em- 

 bedded for many centuries, so completely does 

 peat prevent decomposition and putrefaction. 

 But bog earth and swamps are capable of being 

 rendered extremely fertile; the peat marshes 

 of La Vendee are the most productive in the 

 country; the neighbourhood of Amiens yields 

 excellent vegetables; and the name of marais, 

 or morass, which the market-gardens of Paris 

 still bear, indicates sufficiently the original con- 

 dition of the soil. To render peat fertile it is 

 necessary in the first place to drain it, for until 

 the water is removed the air cannot enter the 

 mass, and without oxygen its elements, espe- 

 cially nitrogen, remain unchanged. 



When dry, and then exposed to the action of 

 air, moisture, and frost, it is readily pulverized, 

 and loses, in a great measure, its astringent 

 principle; the correction of this is greatly aided by 

 the addition of lime, gypsum, or calcareous marls. 



Some kinds of peat will kill the microdemes 

 that cause fermentation, or prevent them from 

 thriving, so that decomposition could hardly 

 occur in presence of any considerable quantity 

 of it. This fact goes far to explain how it is that 

 peat, when used for the bedding of animals or 

 for absorbing their liquid dejections, serves so 

 well to preserve the manure, namely by delaying 

 fermentation. 



A valuable compost for garden purposes may 

 be prepared by mixing peat with a little earth 

 and peat ash, and pouring over it now and then 

 stable drainings or other ammoniacal liquids. 



The peat used in the cultivation of orchids, 

 ferns, &c, consists principally of the decayed 

 roots, rhizomes, and leaves of bracken. It is 

 therefore quite different in its properties from 

 the peat described above, and is in fact more 

 of the nature of leaf-mould. It is a perfectly 

 safe material to use in the cultivation of all 

 kinds of plants, and the most fibrous quality 

 is preferred to all other material by orchid 

 growers. 



