RESOURCES OF THE SOIL 199 



142. RESOURCES OF THE SOIL 



By resources is meant not only the plant food as such, but 

 the total amount of surface material which can be changed 

 into plant food by nature, or by man. It is a great advantage 

 that most of the plant food is still locked up by nature, 

 otherwise man, in his rapacity, would have deprived the soil 

 of its usefulness hundreds of years ago. 



Nature maintains the fertility of the soil by returning to 

 the ground the decayed plant material. Man has done what 

 he can to deplete the resources of the soil by removing from it 

 all the plant growth. Yet, as the farmer becomes more 

 educated in his own work, he is gradually copying nature 

 and considers the land as a factory, rather than as a place 

 from which he can get something for nothing. 



The useful constituents of the soil are carbon, sulphur, 

 oxygen, phosphorus, calcium, soluble silicates, and a few other 

 chemicals, which do not enter into the plant growth to any 

 great extent. We are often misled by a chemical analysis 

 of the soil, for it shows the total amount of material present 

 in the soil, without stating whether that material is available 

 for plant food. Thus, chemical analyses may show a soil 

 to be rich in everything that goes to produce plants, and yet 

 it may be incapable of sustaining plant life. What we are 

 interested in chiefly is the amount of available plant food 

 that is, the food which the plants can obtain readily from the 

 ground. Fertilization of the land is the addition of the miss- 

 ing constituents of plant food. Besides supplying definite 

 wants, foreign fertilizing material has the further effect of 

 in some way stimulating the plants. 



There is another resource of the soil which is coming more 

 and more to be reckoned as the chief cause of plant growth. 



