180 Bacteria in Relation to Country Life 



Acid soils. — There is an intimate relation between 

 the amount of lime and magnesia and the nitrifying 

 power of the soil. It should be remembered that the 

 activity of the organisms leads to the formation of acids; 

 that is, of sour substances, and that in the absence of lime 

 the acids accumulate and react injuriously on the bac- 

 teria. The deleterious effects of acid substances may be. 

 seen readily on light soils, naturally poor in lime, and 

 upon which applications of sulfate of ammonia are made 

 from time to time. A comparatively large amount of lime 

 is required to neutralize the acids formed in the trans- 

 formation of ammonia salts to nitrate. Because, also, 

 of the severe drain on the lime resources of the soil, 

 the acid conditions become more pronounced. In soils 

 in which large amounts of nitrogen are being nitrified 

 there is a continuous production of the nitrates of lime 

 and magnesia, which are either taken up by the crops or 

 removed in the drainage. It is well known, also, that 

 soils yielding large amounts of nitrate, that is, those rich 

 in humus, lose their lime in still other ways. One in par- 

 ticular is on account of the formation of bicarbonate Of 

 lime, which is soluble in the soil-water. It becomes 

 necessary, therefore, on practically all but limestone 

 soils, to apply lime from time to time, lest the soil 

 become sour and the nitrification processes feeble. 



Difference in organisms. — When favorable conditions 

 for nitrification exist, there comes to be established in 

 time a vigorous combination of nitrifying organisms, 

 capable of accomplishing much work in a short time. 

 This circumstance accounts for the marked differences 

 in the nitrifying power of bacteria from different soils. 



