ON MANURES. 7 



contain in their unchanged states most of the principles which 

 conduce to the life of plants; but there are few cases in which 

 they can be applied to their production in a pure form, for vege- 

 table manures in general contain a portion of fibrous, woody, and 

 insoluble matter, which must undergo some chemical change 

 before they can be converted to the purposes of vegetation. 



Fossil or mineral manures, though not containing nutritive 

 matter,* yet materially assist in the development of the powers 

 of the soil, and in the decomposition of other substances con- 

 tained in it, which they combine in a manner which enables 

 plants to appropriate the kind of nourishment best adapted to 

 their growth, and thus promotes vegetation. As the soil, how- 

 ever, is of infinite variety, so the nature of these manures re- 

 quires more care and discrimination in their application than 

 those composed of vegetable and animal matter ; for an excess 

 of the latter can only occasion immediate rankness in the 

 present crop, while an undue proportion of the former may for 

 a long lime be productive of very serious injury to the land. 



Tiie action of manure upon the soil is commonly expressed 

 by saying, ' that it fertilizes the land ;' and that is generally 

 deemed sufficiently intelligible to common comprehension; but 

 it is of great importance to both the theory and the practice of 

 agriculture to disthiguish the properties and the mode of appli- 

 cation by which each of these manures is made productive of 

 that eftect ; and it is only by means of an acquaintance with 

 their composition that we can form any safe conclusion regard- 

 ing their respective merits. Besides the distinction already 

 drawn between the vegetable, animal, and mineral substances, 

 manures of the same kind in some cases act difi^erently, — in 

 the one resisting putrefaction, and in the other promoting it. 

 Among the former are several species of salts, formed from the 

 ashes of burnt vegetables, the dung of fowls, that of horses in 

 wjme states of preparation, and quicklime. Among the latter 

 are certain salts found in calcareous earths; liiT^;?, which, after 

 liaving been burnt and allowed to rest during a few months, 

 converts all the putrescible matter contained in the soil into a 

 scrt of mucilage; and horse-litter, which, when in a forward 

 state, becoines a stimulant from the salts contained in it, and 

 thus also promotes putrefaction. It must also be observed, 

 tiiat several of these manures acquire different properties 



* Lime, however, though not considered nutritive, yet forms, in very 

 minute portions, a component part of plants and the bones of anLmals. 

 B 



