[379] SCIENTIFIC MANUAL. 93 



monstrated by analysis, does not yet assure us that it is 

 present in an available condition, so as to be ready for ab- 

 sorption by the plant ; for the agents which the chemist uses 

 in his laboratory are much more powerful than those placed 

 at the command of vegetables by nature ; thus far then, 

 mere ultimate analysis is not a direct indication of the pro- 

 ducing powers of the soil. 



"This consideration becomes of most serious moment, 

 where the rocks from which the soils are originally derived 

 are in close proximity, so that a large amount of unde- 

 composed material may be supposed to be unevenly diffused 

 throughout the soil." 



In South Georgia, where the soils have been brought a 

 long distance, and have become more thoroughly inter- 

 mingled and comminuted, an analysis of a sample, properly 

 selected, would probably indicate very nearly the compo- 

 sition of the soil of a large area. 



The analysis of crops is important in connection with 

 that of soils and manures. 



" The determination of the kind and quantity of the 

 mineral ingredients which crops withdraw from the soil is 

 at least equally important with that of the soils them- 

 selves. It informs us what, and how much, the soil has 

 lost in cultivation, and thus enables us to select judiciously 

 the most economical mode of replacing the drain ; provi- 

 ded, of course, that the composition of the fertilizers at our 

 command be also known to us." Ibid. 



Soil exhaustion is the result of the withdrawal of the ash 

 ingredients of the crops removed, or of denudation by sur- 

 face washing. 



Complete exhaustion never occurs the term, as used, 

 being relative only. Complete exhaustion would imply 

 the entire removal of the mineral elements of plant-food 

 from the soil. This is not the sense in which the term is 

 here used. A soil is said to be exhausted when it ceases 

 to produce remunerative crops. This may result from the 



