IX.] LIMING 261 



temperatures. The subject is still obscure, but these 

 effects of heating the soil may well be a factor in the 

 value of such processes. 



A variation on the old process of " clod burning " 

 consists in " border burning," in which clay is dug from 

 one corner of the field and burnt by means of the couch 

 and other weeds cleaned off the land, the hedge trim- 

 mings, etc. ; the burnt clay is then spread over the 

 surface to improve the texture of the soil. Without 

 doubt the latter process might still be profitably adopted 

 where heavy clay land is under the plough ; if every 

 year some clay were added to the fires made from the 

 weeds and hedge trimmings, valuable material for 

 lightening the soil would be obtained without wasting 

 too much soil nitrogen. 



Of course the incorporation of any large-grained 

 material will improve the texture of clay soils ; in some 

 cases sand has been dug and spread with advantage ; 

 road scrapings, town refuse, and even coal ashes help 

 to lighten the soil, though, in the case of gardens, coal 

 ashes should be avoided. 



Liming and Chalking. 



Of all the methods of improving the soil, other 

 than actual manuring or cultivation, none is more 

 important than the incorporation of lime or chalk. 

 It has already been indicated that many soils exist, 

 chiefly clays and sands, containing less than 1 per cent, 

 of carbonate of lime ; on all such land liming produces 

 very pronounced effects, both on the physical texture of 

 the soil and on the character of the resulting vegetation. 



It is on the clays and other strong soils that lime 

 produces the greatest alteration in texture; its effect 

 in coagulating and causing the finer particles to form 

 into aggregates, which remain loosely cemented by 



