'70 DRY- FARMING 



ditions arc favorable, it encourages bacterial life, 

 which, as is now a well-known fact, is an important 

 factor in developing and maintaining soil fertility. 

 (3) By somewhat subtle chemical changes it makes 

 the relatively small j^ercentages of other plant-foods, 

 notably phosphoric acid and potash, more available 

 for plant growth. (4) It aids to convert rapidly 

 organic matter into humus which represents the main 

 portion of the nitrogen content of the soil. 



Of course, an excess of lime in the soil may be 

 hurtful, though less so in arid than in humid re- 

 gions. Some authors state that from 8 to 20 per 

 cent of calcium carl^onate makes a soil unfitted for 

 plant growth. There are, however, a great many 

 agricultural soils covering large areas and yielding 

 very abundant crops which contain very much larger 

 quantities of calcium carbonate. For instance, in 

 the Sanpete Valley of Utah, one of the most fertile 

 sections of the Great Basin, agricultural soils often 

 contain as high as 40 'per cent of calcium carbonate, 

 without injury to their cr(jp-produeing power. 



In the table are two columns headed "Soluble 

 Silica" and "Alumina," in both of which it is evident 

 that a very much larger ])er cent is found in the arid 

 than in the humid soils. These soil constituents 

 indicate the condition of the soil with reference to 

 the availability (.)f its fertility for plant use. The 

 higher the percentage of soluble silica and alumina, 

 the more thoroughly decomposed, in all probability. 



