VALUE OF SILT ANALYSIS 77 



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 hydration. 

 The per cent, of humus, as will be explained in the 

 next chapter, does not represent all of the organic 

 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 analysis, like an isolated analysis of 

 well water, frequently fails in its object because of a 

 lack of proper normal standards for comparison. 

 When extended series of soil analyses have been 

 made, much valuable information has been obtained. 



Suppose a soil contain 0.40 per cent, of acid-soluble 

 potash and field experiments indicate that there is a 

 deficiency of available potash. This may be due to 

 some abnormal condition of the soil, as an insufficient 

 amount of other alkaline compounds as calcium car- 

 bonate to take the place of the potash which has been 

 withdrawn by the crop, in which case the deficiency 

 of potash can be remedied without purchasing solu- 

 ble potash fertilizer, to become insoluble by fixation 

 processes. If a soil contain only 0.04 per cent, of 



