MANURES. 



MANURES. 



much smaller quantities than the earthy; and, 

 3. The saline, which are the most sparingly 

 applied of all fertilizers, are the most readily 

 absorbed by plants, and whose period of dura- 

 tion in the soil is longer than the organic, but 

 less than the earthy. A manure is either use- 

 fur to vegetation, by affording, in its simple or 

 decomposed state, direct food or constituents, 

 or else it is a fertilizer, by adding to the soil 

 additional power to absorb and retain atmo- 

 spheric gases and moisture. We shall see, 

 hereafter, that most manures which are com- 

 monly applied to the land assist the growth of 

 plants in both ways. Looking at the question 

 abstractedly, it must be evident, that as animals 

 receive almost the whole of their nutriment 

 either directly or indirectly from the vegetable 

 kingdom, their excrement, or their decomposed 

 bodies, returning these to the soil, must form 

 the best manure. 



With regard to inorganic substances, clay 

 of the earthy manures, and some of the saline 

 fertilizers, act principally by their absorption 

 and retention of moisture. Gypsum, it is true, 

 enters into the composition of some of the 

 grasses, and, in minute proportions, other salts 

 do the same ; but, if we except phosphate of 

 lime (the earthy salt of bones), none of the 

 salts can be considered to be a very general 

 direct food of plants. Davy very clearly ex- 

 plains the desirable objects in the fertilization 

 of soils : he says, "The plants growing in a 

 soil incapable of supplying them with sufficient 

 manure or dead organized matter, are generally 

 very low, having brown or dark-green leaves, 

 and their woody fibre abounds in earth. Those 

 vegetating in peaty soils, or in lands too co- 

 piously supplied with animal or vegetable mat- 

 ter, rapidly expand, produce large bright-green 

 leaves, abound in sap, and generally blossom 

 prematurely. Excess of poverty or riches is 

 almost equally fatal to the hopes of the farmer; 

 and the true constitution of the soil, for the 

 best crop, is that in which the earthy materials, 

 the moisture, and manure are properly asso- 

 ciated, and in which the decomposable vegeta- 

 ble or animal matter does not exceed one-fourth 

 of the weight of the earthy constituents." (Ele- 

 ments ofdg. Chem. p. 264.) 



Of the organic manures, those which the 

 most readily putrefy are the most rapid in their 

 effects ; but then they are the most speedily 

 exhausted: thus oil and fish, the most rapid of 

 fertilizers, are exhausted by the few first crops; 

 while bones, which decay more slowly, will 

 last some time longer. The effect of chopped 

 woollen rags is excellent for two years in the 

 rich clay hop-gardens of Kent, and for three or 

 four in the light, chalky, arable soils of the 

 valley of the Kennett. Farm-yard dung, when 

 applied in different states of freshness, illus- 

 trates the same position. M. Hassenfratz ma- 

 nured two pieces of the same kind of soil, the 

 one with a mixture of dung and straw highly 

 putrefied, the other with the same mixture newly 

 made, and the straw almost fresh ; he observed, 

 that during the first year the plants which grew 

 on the land manured with the putrefied dung 

 produced a much better crop than the other; 

 but the second year, the ground which had 

 been manured with the unputrefied dung pro- 

 770 



duced the best crop : the same result appeared 

 the third year ; after which both seemed to be 

 equally exhausted. "Another experiment of 

 the same chemist," adds Dr. Thomson, " ren- 

 ders this truth still more evident. He allowed 

 wood-shavings to remain in a moist place for 

 about 10 months, till they began to putrefy, and 

 then spread them over a piece of ground as a 

 manure. The first 2 years this piece of ground 

 produced nothing more than others which had 

 not been manured at all ; the third year it was 

 better ; the fourth year it was still better ; the 

 fifth year it reached its maximum of fertility; 

 after which it declined constantly till the ninth, 

 when it was quite exhausted." 



It is of the highest importance to the cult^ 

 vator that he obtains a correct knowledge of 

 the mode in which those manures operate which 

 are found to be advantageous to the growth of 

 his crops. He must discard from his mind all 

 those false conclusions which are sometimes 

 drawn with regard to an imaginary power as- 

 signed to plants of generating vegetable sub- 

 stances, for they can effect no such miraculous 

 results. It is true that they can combine the 

 gases or elements of vegetable matters together, 

 and form gluten, starch, gum, sugar, woody 

 fibre, &c. ; they can absorb and arrange with 

 these the earths and saline bodies ; but the 

 oxygen, the carbon, the nitrogen, and the hy- 

 drogen, of which the first-named are composed, 

 and which plants usually obtain from either 

 the atmosphere or by the decomposition of or- 

 ganic matter, they can no more create than 

 they can form the lime or the silica, which are 

 as commonly present in most vegetables as 

 sugar, gum, or woody fibre. Davy proved this 

 when he made a plant of the oat grow in pure 

 carbonate of lime, and watered it with pure 

 distilled water. It grew but languidly, and al- 

 though it had a free supply of the atmospheric 

 air, yet the access of all dust was carefully pre- 

 vented. Upon analyzing the plant, it was found 

 to have much increased in carbonate of lime, 

 but its silica or flint was rather diminished, a 

 grain of oat being found to yield more : this 

 Davy attributed to the loss of its husk during 

 vegetation. (Lectures, p. 31Z.) Whatever earthy 

 or saline matters, therefore, are found in vege- 

 tables, must have been either derived from the 

 natural soil or furnished by the manures added 

 to it whether it be carbonate of lime (chalk), 

 or silica (earthy matter of flint), alumina (clay), 

 sulphate of lime (gypsum), or phosphate of 

 lime (earthy salt of bone). It should also be a, 

 received axiom with the farmer, that there is! 

 no part of any decomposing animal or vegeta- 1 

 ble manure but what is, either in its gaseous or 

 solid state, the natural food of plants : thus the 

 gases emitted by the putrefaction of a dunghill 

 are so much lost to the vegetable matters of the 

 soil, and such an injury is never submitted to 

 by the intelligent cultivator, but from an una- 

 voidable necessity. Hence the value of green 

 manures ; for in these cases every portion of 

 the decaying and fermenting fertilizer is gra- 

 j dually absorbed by the roots and leaves of the 

 j succeeding crop. 



When the cultivator is in doubt with regard 

 to the possible advantages of any manure, 

 whether earthy, saline, vegetable, or animal, 



