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ON THE USE OF LIME, MARL, AND SHELL-SAND. 



II. FUNCTIONS OF LIME UPON THE SOIL AND VEGETATION. 



Having described the physical and chemical properties of 

 several kinds of limestones, marls, sea-sand, and other calcareous 

 mineral substances, occurring in the West of England, I shall 

 now proceed to refer to the functions which lime is supposed to 

 exercise upon the land and upon vegetation. 



Unless the agriculturist entertain correct views with regard 

 to the theory of the action of lime, he is as likely as not to mis- 

 apply it and to meet with disappointment. For this reason it 

 may not be out of place to allude briefly to the functions of lime. 



There are especially four functions requiring particular notice : 



1. Lime exercises a mechanical effect upon the land to which it is 

 applied. 



Stiff, heavy clay land by its addition is rendered more porous, 

 friable, and consequently better adapted for cultivation. Sandy, 

 light soils, on the other hand, when limed, are consolidated, and 

 thus improved in their physical condition. 



2. Lime supplies food to plants. 



All naturally fertile soils contain a notable proportion of lime, 

 while in those which are naturally unproductive the quantity of 

 lime is comparatively small. It is on soils of the latter descrip- 

 tion that lime is added with much benefit ; and we may therefore 

 safely conclude that it is really indispensable to the fertility of 

 the soil. 



All our cultivated plants on burning furnish ashes, containing 

 more or less lime. It thus appears that it is a necessary food of 

 plants without which they cannot come to perfection ; and as 

 plants have not the power within themselves to generate lime, 

 we can readily understand the benefits which result from its 

 application to soils naturally deficient in it or impoverished by 

 long-continued cropping. 



The quantity of lime actually removed from the soil by dif- 

 ferent crops varies considerably. Some plants require a much 

 larger amount than others. Thus it has been found that in the 

 produce of an acre of land of the following crops there is con- 

 tained of lime : 



