SOIL SANITATION 295 



their fertilizer requirements, and one is 

 tempted to ask to what extent the different 

 fertilizer requirements of different soils, or of 

 the same soil under different conditions, may 

 be influenced by the same cause. That harm- 

 ful bodies occur in soils has been amply shown, 

 and that these are influenced directly or indi- 

 rectly by fertilizer salts is also clear from 

 these and other researches. 



"That the constitution of the organic mat- 

 ter varies from soil to soil and in the same 

 soil under different conditions of aeration, 

 drainage, and cropping is likewise clear. The 

 presence of compounds inimical to plant 

 growth by virtue of a property resembling 

 that of any of the above-mentioned substances 

 might, therefore, cause a different fertilizer 

 requirement, a requirement which might even 

 change from time to time, according to the 

 nature of the biochemical relations producing 

 the body or according to the nature of the 

 plant remains in the soil; in other words, ac- 

 cording to the rotation, with its necessary 

 altered soil management, and the altered bio- 

 chemical changes produced in the different 

 plant remains." 



***** 



"Organic matter is very changeable; it is 

 the material which forms the food, as it were, 

 of all the microorganisms of the soil, of the 

 bacteria, of the molds, of the protozoa, and in- 



