VALUE OF SILT ANALYSIS 75 



is of no value. Other solvents than hydrochloric acid 

 are used in soil analysis with excellent results. Hydro- 

 chloric acid is generally used because it represents the 

 limit of fhe solvent power of plants. 17 . The figures 

 obtained by the use of hydrochloric acid are valuable 

 inasmuch as they indicate whenever an element is 

 present in amounts which are too limited to admit of 

 crop production. Suppose a soil contain 0.02 per cent, 

 of acid-soluble potash; this would be too small an 

 amount to produce good crops. On the other hand, 

 the soil might contain 0.5 per cent, and yet not have 

 sufficient available potash for crop growth. Hence 

 it is, that in interpreting results, the hydrochloric acid 

 solvent may show when a soil is wholly deficient in 

 any one element, as is sometimes the case, but it does 

 not necessarily show a deficiency in the case of a soil 

 rich in acid-soluble potash ; this can, however, be ap- 

 proximately indicated, by the use of other solvents, as 

 explained in Section 91. Hydrochloric acid is mainly 

 valuable in determining the general character of the 

 soil, rather than its amount of available plant food. 



In the analysis of soils their reaction as acid, alka- 

 line, or neutral, should be determined, because plant 

 food exists in a different form in each class of soils. 

 If a soil contain from 0.3 to 0.5 per cent, or more of 

 lime and from o.i to 0.4 per cent, of combined carbon 

 dioxide, and is not strongly alkaline, there is a reason- 

 able content of lime carbonate. If, however, the soil 

 contain only a trace of carbon dioxide, the lime is 

 not present as carbonate, but is probably present as a 



