COMMERCIAL FERTILISERS 399 



Fertilisers are so easy to get and easy to apply, 

 that there is a tendency to use them hastily, 

 without regard to their content and the needs of 

 the soil ; and to use them in much larger quantities 

 than is really necessary. The rational course to 

 pursue is to use them only to supplement farm re- 

 sources of fertility; and to use them only up to the 

 point where they return the largest ratio of profit 

 for the expenditure. 



Certain materials that furnish little if any actual 

 plant food, but exert a very beneficial effect upon 

 the soil , are called ' ' indirect fertilisers " or " amend- 

 ments." The most common of these are lime 

 and land plaster and, to a very slight extent, salt. 



THE BENEFITS OF LIMING 



Lime is an important factor in maintaining the 

 fertility of certain farm soils. It is a plant food. 

 If a soil contained no lime, plants would not 

 thrive upon it. Although most soils contain 

 sufficient lime for the needs of the crop, some soils 

 become exhausted of it and it is then needed not as 

 an indirect, but as a direct, fertiliser. 



Lime may benefit certain soils by improving 

 their texture. When applied to a light, leachy 

 soil, it makes it more retentive. When applied to 

 a clay, it has the opposite effect; the very fine soil 

 grains are cemented together and consequently 

 the soil is made more porous. The practical 

 effect is that liming a sandy soil makes it less 

 leachy, while liming a stiff clay makes it more 

 crumbly; the condition of both is greatly improved. 



A third effect of applying lime to a soil that is 

 deficient in it, is that it makes the plant food in 

 the soil, especially the potash, more soluble. 



