SOIL SANITATION 289 



to the best advantage. Therefore, we apply 

 lime. 



It is doubtful if normal soils are deficient 

 in lime so far as plants require it as a mineral 

 food. Some crops, such as the legumes, are 

 heavy feeders of lime and require that a bal- 

 ance be maintained by actually adding lime 

 in exceptional instances. But by far the most 

 important function of lime is to cleanse the 

 soil and make it habitable for the hosts of 

 bacteria which are at work therein. 



It is a common experience with farmers on 

 soils that have been heavily cropped for many 

 years to see alfalfa or clover fail utterly unless 

 lime be added and harrowed into the soil. An 

 analysis of that soil would probably show that 

 calcium carbonate was present in sufficient 

 quantities to feed the legume. But a test of 

 the soil with litmus paper would show that the 

 acids of the soil, the ferments of decaying green 

 vegetation not properly controlled, had ren- 

 dered the soil "sour," as the saying goes. 

 "Sour" soil will not grow legumes; although, 

 on the other hand, it is considered necessary 

 by many farmers for growing potatoes with- 

 out scab. Potatoes can be grown on the same 

 soil year after year, if green rye or other green 



