QO SOILS AND FERTILIZERS 



soluble in hydrochloric acid and produce good crops. 

 While these conditions are frequently observed, it does 

 not necessarily follow that the chemical analysis of a 

 soil is of no value, as often the results are not correctly 

 interpreted. Then, too, other solvents than hydro- 

 chloric acid are used for determining the more active 

 forms of plant food. Hydrochloric acid is generally 

 used because it represents the limit of the solvent power 

 of plants. 9 The figures obtained by the hydrochloric 

 acid solvent are valuable, as they indicate whenever an 

 element is present in amounts too limited for crop pro- 

 duction. 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 avail- 

 able 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 ele- 

 ment, as sometimes occurs, but it does not necessarily 

 show a deficiency in the case of a soil rich in acid- 

 soluble potash ; this can, however, be approximately 

 indicated, by the use of other solvents, as explained 

 in previous sections. Hydrochloric acid is mainly val- 

 uable in determining the general character of the soil, 

 rather than its amount of available plant food. 



104. Interpretation of Soil Analysis. In the analysis 

 of soils their reaction as acid, alkaline, or neutral, should 

 be determined, because plant food exists in a different 



