THE MAIN TYPES OF SOIL 47 



affect the fixation are the lime, iron, and 

 similar bases that are naturally present 

 in abundance in all soils. In the case of 

 ammonia it is probable that the most im- 

 portant fixing agent is humus, which, as is 

 well known, has great power of mechanically 

 storing up ammonia in its tissues. We have 

 a good example of the affinity of humus for 

 ammonia in the fact that where moss litter 

 which is a form of humus is used in stables 

 the atmosphere is much less redolent of 

 ammonia than where the litter is straw. 



As regards soils, it is found that the least 

 power of absorption is possessed by sand, 

 while the property is most conspicuous in 

 strong loams, clay, and soils that contain 

 much decomposing vegetable matter. 



CHAPTER III 



THE MAIN TYPES OF SOIL 



WHILE soil is in many respects a very 

 complex substance it can, from the agri- 

 cultural point of view, be regarded as com- 

 posed mainly of four substances, that is to 

 say, in all soils one or other of these four 



