1 IS CALCAREOUS MANURES-PRACTICE. 



CHAPtER XII. 



THE PERMANENCY OF CALCAREOUS MANURES, AND OF ALIMENTARY OR PUTRES- 

 CENT MANURES, WHEN COMBINED , WITH THE CALCAREOUS. 



Proposition 5— continued. 



It was stated, (page 70) that the ground on which an old experiment 

 was made and abandoned as a failure, more than sixty years ago, still con- 

 tinues to show the effects of marl. Lord Kames mentions a fact of the 

 continued beneficial effect of an application of calcareous manure, which 

 was known to be one hundred and twenty years old.* Every author who 

 has treated of manures of this nature, attests their long duration. But 

 when they say that they will last twenty years, or even one hundred and 

 twenty years, it amounts to the admission that at some future time the 

 effects of these manures will be lost. 1 his I deny — and from the nature 

 and action of calcareous earth, claim for its effects a duration that will 

 have no end. 



If calcareous earth, applied as manure, is not afterwards combined with 

 some acid in the soil, it must retain its first forni, which is as indestructible, 

 and as little liable to be wasted, by any cause whatever, as the sand and 

 clay that form the other earthy ingredients of the soil, 'i'he only possible 

 vent for its loss, is the very small proportion taken up by the roots of 

 plants, which is so inconsiderable as scarcely to deserve naming. 



Clay is a manure for sandy soils, serving to close their too open texture. 

 When so applied, no one can doubt but tl.at this effect of the clay will last 

 as long as its presence, or as long as the soil itself Neither can calcareous 

 earth cease to exert its peculiar powers as a manure, any more than clay 

 can, by the lapse of time, lose its power of making sands more firm and 

 adhesive. Making due allowance for the minute quantity drawn up into 

 growing plants, it is as absurd to assert that the calcareous earth in a soil, 

 whether furnished by nature or not, can be exhausted, as that cultivation 

 can deprive a soil of its sand or clay. 



But on my supposition that calcareous earth will change its form by 

 combining with acid in the soil, it may perhaps be doubted by some whe- 

 ther it will be equally safe from waste under its new form. It must be ad- 

 mitted that the permanency of this compound cannot be proved by its 

 insolubility, or other properties, because neither the kind nor the nature of 

 the salt itself is yet known. f But judging from the force with which good 

 neutral soils resist the exhaustion of their fertility, and their always pre- 

 serving their peculiar character, it cannot be believed that the calcareous 

 earth, once present, has been lessened in durability by its chemical change 

 of form. It was contended that the action of calcareous earth is absolutely 

 necessary to make a poor acid soil fertile ; but it does not thence follow 

 that other substances, and particularly this salt of lime, may not serve as 

 well to preserve the fertility bestowed at first by calcareous earth. All that 

 is required for this purpose, is the power of combining with putrescent 

 matter, and thereby fixing it in the soil ; and judging solely from effects, 



• Gentleman Farmer, page 266, 2d Edin. edition. 



t This passage is left as it stood in the first edition, before the discovery of the humic 

 acid was known. Indeed no aid has been derived from that discovery, nor any change 

 of language made in consequence of it, except by inserting the quotation respecting 

 this substance, and the remarks thereon, at page 53. 



