MANURES. 



he need only ask himself this question : Does 

 this manure contain any constituents found in 

 my crops, and is the land I cultivate deficient 

 in any of them 1 An inattention to this consi- 

 deration has been the cause of much disap- 

 pointment and many mistaken conclusions : 

 for instance, on many soils the application of 

 gypsum to artificial grasses, and even to tur- 

 nips, is very useful ; on others it produces no 

 effect. Strange opinions were in consequence 

 long entertained with regard to this manure 

 until it was found that the soils on which it 

 was valueless naturally contained it in abun- 

 dance, and that those soils in which it did so 

 much good were nearly or entirely deficient in 

 this essential ingredient of clover, lucern, &c. ; 

 for it was now evident, that to add gypsum to 

 a soil which already contained it in sufficient 

 quantities, was as needless as to add sand to a 

 sandy, or clay to a clayey soil. 



There is little doubt but that plants derive 

 all their constituents from the soil or the air, 

 in either the gaseous or liquid state ; that in 

 the light they absorb carbonic acid gas and 

 emit oxygen is well known ; by this means, 

 therefore, they readily obtain the necessary 

 supply of carbon. The hydrogen of vegetable 

 substances is most probably furnished by the 

 decomposition of either water or the carbu ret- 

 ted hydrogen emitted during the putrefaction 

 of animal and vegetable substances. This 

 latter seems peculiarly grateful to plants in 

 those situations where it is copiously emitted, 

 as near to stagnant pools, over drains, &c., 

 where vegetation is always rank; and when 

 present in the atmosphere, as in coal-mines, 

 the green colour of plants growing in it is pre- 

 served even when they are deprived of light. 

 The earthy or saline matters of vegetables, 

 such as silica, carbonate, phosphate, and sul- 

 phate of lime, &c., are all in minute propor- 

 tions soluble in water ; they are found more or 

 less in all cultivated soils, and when they are 

 deficient, their addition, as I have before ob- 

 served, constitutes the great art of manuring : 

 but there are such endless varieties of soils, 

 that there is hardly a manure that will suit 

 every description each soil must be separately 

 examined practice is the only substitute for 

 chemical investigations. 



Thus, wood-ashes of the beech or bone- 

 powder form excellent manures for soils defi- 

 cient in the phosphates ; lime, where chalk is 

 altogether absent, and so on ; and whilst we 

 attend to the nature of the soil, we must also 

 ever recollect, as one of the most important 

 principles of agriculture, that whatever is com- 

 pletely removed from a soil by crops, must be in 

 some way or other restored by artificial means. 



That various earthy, animal, and vegetable 

 substances, when applied to the roots of plants, 

 accelerate their growth, has been known from 

 a very early period; but in what manner these 

 fertilizers serve as the food of vegetables has 

 not been certainly determined. That they 

 must all be in a fluid state, is supposed to be 

 absolutely necessary: thus all the attempts of 

 Sir Humphry Davy to make plants absorb the 

 fine impalpable powder of charcoal obtained 

 by washing gunpowder entirely failed. 



MANURES. 



! The soluble matters consumed by plants are 

 probably, in general, absorbed by their roots 

 unaltered, although, in other cases, decomposed 

 during their absorption. In the experiments 

 J of Davy, he caused the roots of some plants 

 ! of mint to be analyzed, which had grown both 

 in pure water and in sugar and water. 120 

 grains of the roots of the mint which had 

 grown in common water yielded 3 grains of 

 deep olive extract, of a sweetish and astringent 

 taste; 120 grains of the roots which had grown 

 in sugar and water afforded 5 grains of pale 

 greenish, sweetish extract, not so astringent as 

 the other. (Lectures, p. 270.) These experi- 

 ments, therefore, are evidently in favour of the 

 opinion that plants absorb many of the con- 

 stituents of manures in an unaltered state, and 

 the experiments of the late Mr. G. Sinclair 

 with saline substances are still more decisive. 

 See SALTS. 



The roots are the chief organs for absorbing 

 the food of plants ; and of the roots it is nearly 

 established that the extremities, or spongioles, 

 are the only parts which have the power of 

 absorption; and hence one reason why they 

 increase in length as the soil at their extremi- 

 ties is exhausted of nourishment. It is from 

 this cause that liquid manure is so valuable a 

 fertilizer; for in the dissolution of the excre- 

 ments of animals in water, as practised so ad- 

 vantageously in foreign countries, and long 

 ably recommended by Mr. Knight, the late 

 president of the Horticultural Society, for the 

 adoption of the English farmers, the dung is 

 merely rendered more easily soluble by the 

 plant, and better diffused in the land. No new 

 compound is formed by the mixture ; the action 

 of the dung, mixed with four or five times its 

 weight of water, is apparently much less ener- 

 getic; and yet this plan is decidedly advan- 

 tageous, successfully produces the most luxu- 

 riant crops, is an old practice on the Continent, 

 is gaining ground in England, and the more it 

 is known the oftener it will be adopted. Yet 

 hitherto in England much too little general 

 attention has been paid to liquid manures; by 

 many farmers the drainage of the farm-yard 

 and the house is generally disregarded, and 

 allowed to escape in the best way it can, into 

 the nearest ditch or river, being supposed to 

 contain nothing that is the food of plants ; and 

 this, too, by the very same persons who are 

 particularly careful in the preservation, as 

 food for their hogs, of every portion of a mise- 

 rable dish of cabbage-water. See LIQ.UID MA- 

 NURE. 



There are certain properties in which all 

 fertilizers, to a certain extent, agree: thus 

 they all contain one or more vegetable con- 

 stituents, and they have all a strong attraction 

 for atmospheric moisture (the insensible va- 

 pour always contained in the atmosphere). 

 This property is of very considerable advan- 

 :age to vegetation. The comparative powers, 

 'n this respect, of various manures may be 

 udged of from the results of my experiments, 

 which will be found in the following table. In 

 these the animal matters were employed with- 

 out any admixture of straw. (Essay on>Salt, p. 

 819.) 



771 



