304 CAUSES -OF FERTILITY AND STERILITY [chap. 



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 I 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 

 the carbonate of lime, has already been discussed. 

 The soil becomes much less retentive of water, perco- 

 lation is increased so that the limed land is drier 

 and warmer, admits of cultivation at an earlier date 

 in the spring, and is far more friable when dry. 

 In fact, the liming gives a coarser texture to the clay 

 soil, and all the effects pertaining to the coarser texture, 

 such as diminished capacity for retaining water and 

 consequent greater warmth, less shrinkage and tendency 

 to cake on drying, are all manifest after the application 

 of lime. It does not, however, follow that the crop 

 will mature more readily though the season is made 

 earlier through liming ; in many cases in dry seasons 

 crops upon clay ripen prematurely, because the drying 

 up and shrinkage of the impervious clay cut the 

 roots off from all access of moisture. The liming, 

 by opening up the soil to the motion of water by 

 surface tension, keeps the plant growing for a longer 

 period ; at the same time, the increased amount of plant 



