78 SOILS AND FERTILIZERS 



fication. The appearance of the crop is the best indi- 

 cation as to a deficiency of nitrogen. 



A soil which contains less than 0.15 per cent, of pot- 

 ash soluble in hydrochloric acid is quite apt to be de- 

 ficient. Soils which contain 0.5 per cent, or more of 

 lime carbonate will produce good crops on a smaller 

 working supply of potash than soils which are poverty- 

 stricken in lime. As a rule the best agricultural soils 

 contain from 0.3 to 0.6 per cent, of potash. Sandy 

 soils of good depth may contain less plant food than 

 the figures given, and not be in need of fertilizers. 



The term volatile matter is sometimes confused with 

 the term organic matter. The volatile matter includes 

 the organic matter and the water which is held in 

 chemical combination as in the hydrated silicates. 

 A soil may have a high per cent, of volatile matter 

 and contain very little organic matter. Indeed all 

 clays contain from 5 to 9 per cent, of water of hydra- 

 tion. The per cent, of humus, as will be explained 

 in the next chapter, does not represent all of the or- 

 ganic matter. 



The best results are obtained from soil analyses 

 when an extended study is made of the soils of a lo- 

 cality. Then an unknown soil of that locality can be 

 compared with a productive soil of known composition. 

 An isolated soil analvsis, like an isolated analvsis of 

 well water, frequently fails in its object because of a 

 lack of proper normal standards for comparison. 



