THE SOIL 307 



soils have been ruined by ignorance and carelessness. 

 In recent years farmers have begun to learn how to make 

 soils productive and how to keep them fertile. 



213. Physical Composition of the Soil. In the preced- 

 ing section is given the origin of two of the important 

 parts of a productive soil. The greater portion by weight 

 of most soils is composed of decomposed rock or rock 

 particles, but no crop could grow on a soil composed en- 



A HILLSIDE PROPERLY CULTIVATED TO PREVENT EROSION 



tirely of distintegrated rock. A soil which is suitable for 

 agricultural purposes is made up of five important parts, 

 namely, (i) disintegrated rock, (2) soil water, (3) soil 

 air, (4) humus or decaying organic matter, and (5) bac- 

 teria and other living organisms. 



Not many kinds of crops can be produced in soil which 

 lacks any one of these five parts. Much soil which is 

 found in some swampy regions is made up largely of de- 

 caying organic matter. It is valuable for growing onions 

 and celery. Soils that do not have the proper amounts 

 of water, air, bacteria, or humus, will not grow large crops. 



