382 MORE OUGHT TO BE LAID ON CLAY, WET, AND MARSHY SOILS, 



the practical farmer could rarely afford. It would be greater economy, 

 therefore, in most cases to add a dose several times larger, and this not 

 only because the same amount of labor would diffuse it more general- 

 ly through the whole soil, but because this larger liming would render 

 less necessary the immediate addition of new supplies to repair the un- 

 avoidable waste. 



But there is reason to believe that the proportion of lime which the 

 soil ought to contain, if it is to be successfully subjected to arable cul- 

 ture, ought to be much larger than is above assumed as the smallest 

 or minimum quantity. If we suppose one per cent, to be necessary, 

 then eight tons of lime-shells, or upwards of 300 bushels of slaked lime, 

 must be mixed with a soil six inches in depth, to impart to it this pro- 

 portion — or half the quantity, if it be kept within three inches of the sur- 

 face. Even a very large dose of lime, therefore, does not, if it be well 

 mixed, materially alter the constitution of the soil. 



2°. But experience has proved that the quantity of lime which a 

 skilful farmer will add to his land will vary with many other circum- 

 stances besides the depth of his soil, and the proportion of lime it al- 

 ready contains. Thus — 



a. On clay lands more lime is necessary than on light and sandy 

 soils. This may be partly ascribed to the physical effect of the lime 

 in opening and loosening the stiff" clay — but independent of this action 

 the particles of lime are liable to be coated over and enveloped by the 

 fine clay, and thus shut out from the access of the air. These parti- 

 cles, therefore, must be more numerous in such a soil, if as many of 

 them are to be exposed to the air as in lighter land, through which the 

 atmospheric air continually permeates. 



b. On wet and marshy soils, a larger application still may be made 

 whh safety, and partly for the same reason. 



The moisture surrounding the lime shuts out the air, without the 

 ready access of which lime cannot perform its important functions. The 

 same moisture tends to carry down the lime and lodge it more speedily 

 in the subsoil. The continued evaporation also keeps such soils too 

 cold (Lee. II., § 7), to allow the chemical changes, which lime in fa- 

 vorable circumstances produces, to proceed with the requisite degree 

 of rapidity. The soluble compounds which are formed as the conse- 

 quence of these changes are, in wet and marshy soils, dissolved by the 

 moisture, and so diluted as to enter in smaller quantity into the roots of 

 plants. And lastly, in certain cases, new compounds of the lime with 

 the earthy and stony matters of the soil are formed, which may either 

 harden into visible lumps of mortar and cement, or into smaller parti- 

 cles of indurated matter, in which the lime is no longer in such a state 

 as to be able to act in an equal degree as an improver of the soil. 



In cold and wet clays, in which all these evil conditions occasionally 

 meet, it is not surprising, therefore, that large doses of lime should 

 sometimes have been added without producing any sensible benefit 

 whatever. (" An instance is mentioned in the Nottingham Report of 

 720 bushels having been laid on an acre of clod clay land without any 

 benefit whatever." — British Husbandry, i., p. 296.) 



c. Again, when the soil is also rich in vegetable matter, lime may 

 be still more abundantly applied. Thus, when a field is at once wet 



