CHEMISTRY OF SOILS 117 



and only to a slight extent, if at all, to the increase in the 

 quantity of calcium compounds. 



Some of the less desirable plants sedges, rushes, etc. 

 are better adapted than grasses for growth in sour soils. 

 When the adverse conditions are removed by application 

 of lime, the growth of grasses is encouraged and the others 

 are crowded ,out. A dressing of lime will often make a 

 pasture white with clover though not a blade of it was to 

 be seen for years previously. The large proportion of 

 calcium found in clovers has given rise to a widely spread 

 idea that this effect is due to the increase of calcium com- 

 pounds in the soil. The same effect has,, however, been 

 observed on soils known to contain a considerable propor- 

 tion of calcium salts other than carbonate. It is not pro- 

 duced by an application of gypsum 1 or similar compounds 

 but only by lime. The favourable influence of lime upon 

 the growth of clovers must, therefore, be attributed mainly 

 to its action on the soil rather than to a'ny direct effect upon 

 the plant. It is probable that the proportion of soluble 

 calcium salts in the soil is ample, in all but the rarest cases, 

 to provide for the requirements of the crops so far as the 

 supply of this element of plant food is concerned. Never- 

 theless, the soils may be very deficient in lime. 



A dressing of lime is frequently applied to pastures for 

 the destruction of moss, and in some cases is found to be 

 very effective. Moss is found chiefly in low lying or badly 

 drained,wet land, and it grows all the better when it has not 

 to compete with other plants for the available space and 

 food. There is no reason to suppose that the presence of 

 lime in the soil is actually inimical to the growth of moss. 

 It flourishes on land that is not conspicuously deficient 

 in lime, and applications of that substance often make very 



1 Gypsum is said to have a favourable effect on the growth of 

 clovers in some cases, but such is not the writer's experience. 



