CHAPTER XIII. 



MANURES. 



§ 1. — KINDS OF THEM, ETC. 



Various materials, under the general denomi- 

 nation of manures, have from the earliest ages 

 been applied to the soil, with a view to increase 

 its fertility, or, in other words, to supply plants 

 with those elements necessary for their healthy 

 development, in which the soil may be either 

 naturally deficient, or which have been extracted 

 from it by previous crops. Hence the great im- 

 portance of ascertaining, first, what elements 

 the soil is really deficient in ; and, next, what 

 the material added contains necessary for the 

 crop to be reared. All plants do not require 

 the same food, and hence, without a knowledge 

 of these important facts, very useless, if not in- 

 jurious additions, may possibly be made. It is 

 to arrive at a correct conclusion as to this, that 

 the chemistry of soils and of plants, as well as 

 a practical knowledge of their various natures, 

 is of so much importance ; and without some 

 knowledge of this, all manurial applications 

 whatever must be regarded with suspicion as to 

 the effects they will produce. 



Manures are usually divided into two classes — 

 viz., organic and inorganic ; but more naturally 

 into three — namely, animal, vegetable, and 

 mineral. The first of these comprehends those 

 substances that are derived from animals, either 

 in the shape of excrements or from their dead 

 bodies ; the second includes the vegetables so 

 applied, either singly or mixed ; while the third 

 is composed of minerals, fossils, earths, or earthy 

 substances, either applied in their natural state, 

 calcined, or otherwise reduced in form, or mixed 

 with other materials. Organic manures consist 

 of carbon, hydrogen, and nitrogen, and are un- 

 doubtedly the most valuable. Inorganic man- 

 ures, or the substances employed as such, are 

 very numerous, but the mode in which they act 

 is still very imperfectly understood. Were they 

 as important as some would lead us to believe, 

 they of all others would be the most valuable to 

 the horticulturist, on account of the convenience 

 of their application. Considerable difference of 

 opinion exists as to organic or inorganic matter 

 being the best fertiliser of the soil, Mr Lawes, 

 and with him the majority of practical ex- 

 perimenters, contending for the former, while 

 Liebig, heading the chemical host, as strongly 

 advocates the latter. We are inclined to follow 



the former, so far as the principal supply of the 

 food of plants is concerned, and admit the theory 

 of the latter only in so far as a proportion of 

 certain mineral matters is necessary for the 

 proper action of the organic matter in its prepa- 

 ration as the food of plants, when reduced to an 

 aqueous or gaseous state ; and also that certain 

 minerals enter into the structure of plants, giving 

 them greater strength of stem, and thereby ena- 

 bling them better to maintain an upright posi- 

 tion — a position of all others the most favour- 

 able for the action of atmospheric influences 

 upon their respective organs. The real object 

 of a plant is to reproduce its kind, and when it 

 has done so, as in the case of annuals, it ceases 

 to live— decomposes, and becomes resolved into 

 that matter upon which it had existed, and be- 

 comes the food of plants of its own, or probably 

 of other species. The decay of the annual parts 

 of plants, such as their leaves, &c, in the case 

 of trees, and the higher grades of vegetable life, 

 aids the nourishment of themselves while in life, 

 and fertilises the soil after their removal for 

 other crops. Such is the natural production of 

 organic manure. On the other hand, the advo- 

 cates for mineral or inorganic manures say : 

 Plants, by means of their roots and leaves, per- 

 form the various functions necessary for their 

 existence ; the former penetrate the soil in search 

 of moisture, and of mineral ingredients dissolved 

 by moisture, and essential to the plant; and these 

 materials are taken up by the sap and passed 

 into the leaves, where, by the influence of the 

 sun, the leaves acquire the power of acting on 

 various gases contained in the atmosphere, of 

 absorbing them, and of changing them into ma- 

 terials adapted to their growth. Without the 

 mineral ingredients from the soil, plants could 

 not obtain them otherwise, as none exists in the 

 air. " If we consider," says Mr Nesbit, in 

 " Lectures on Agricultural Chemistry," " the 

 nature of plants, in their wild state especially, 

 we shall find, if they be supplied with an ade- 

 quate quantity of mineral matter according to 

 their varieties, and according to their circum- 

 stances, they will obtain all the rest from the 

 air without any assistance." Mr Nesbit appears 

 to overlook the amount of nourishment plants, 

 even in their natural state, derive from the de- 

 composed remains of their predecessors. 



No doubt, all plants derive a great part of 



