76 SOILS AND FERTILIZERS 



89. Value of Soil Analysis. — Opinions differ as to 

 the value of soil analysis. It is claimed by some that 

 a chemical analysis of a soil is of no practical value 

 because it fails to give the amount of available plant 

 food. A soil may have, for example, 0.4 per cent, of 

 potash soluble in hydrochloric acid and still not 

 contain sufficient available potash to produce a good 

 crop, while another soil may contain 0.2 per cent, 

 of potash soluble in hydrochloric acid and produce 

 good crops. While these facts are frequently true, 

 it does not necessarily follow that the chemical 

 analysis of a soil is of no value because other sol- 

 vents than hydrochloric acid ma}' be used for soil 

 analysis. Hydrochloric acid is used because it repre- 

 sents the limit of the solvent power of plants. The 

 figures obtained by the use of hydrochloric acid are 

 valuable inasmuch as they indicate whenever an ele- 

 ment is present in amounts which are too limited to 

 admit of crop production. Suppose an ordinary soil 

 contains 0.05 per cent, of acid-soluble potash, this 

 would be too small an amount to produce good crops. 

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

 a sufficient amount of available potash. Hence it is, 

 that in interpreting results, the hydrochloric acid sol- 

 vent 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 approx- 



