CHAPTER FOUR 

 HOW TO MAINTAIN FERTILITY 



1 HE soil is a working laboratory in which 

 chemical reactions are constantly going on, mak- 

 ing the various elements available as plant food. 

 In order that a piece of land shall produce a profit- 

 able crop, as much depends upon the mechanical 

 condition of the soil as upon the various chemical 

 elements that it contains which go to make up the 

 structure of the plants grown upon it. Soil is made 

 up of disintegrated rock and decayed vegetable 

 matter, but if it were rock alone it could not sup- 

 port plant life, at least the highly organised plant 

 life upon which we depend for food. In order to 

 support plant life it must have humus, decayed 

 vegetable, and animal matter. Virgin soil contains 

 enough humus to make possible all the necessary 

 chemical changes to produce sufficient plant food, 

 but unless the soil is carefully cultivated and atten- 

 tion paid to the replenishing of it the supply of 



[29] 



