i go THE CHEMICAL ANALYSIS OF SOILS [chap. 



ferric oxide on analysis ; they owe their good qualities 

 to their physical constitution and texture. 



Such further questions as the presence of harmful 

 substances, or even of an excess of more normal con- 

 stituents of the soil, must be considered by the analyst, 

 but will be dealt with in a later section. 



In some cases it will be possible by a chemical 

 analysis to pronounce a given soil to be unsuited to a 

 particular crop : as a rule, however, it is not its chemical 

 composition which fits the land for a particular crop, 

 but its mechanical texture, water-bearing power, drain- 

 age, etc. In most cases the soil can be adjusted to the 

 crop by manure, though the process may be unsound 

 from an economic standpoint, but no expenditure can 

 ever rectify unsatisfactory texture, e.g., convert a light 

 sand into good wheat land. 



Even in considering the chemical analysis of a 

 soil, no hard-and-fast rules can be laid down, the 

 judgment and experience of the analyst must come into 

 play in deciding how far the deficiency or excess of one 

 constituent is likely to affect the action of some of the 

 others : and again, how far the texture, the aspect, and 

 other factors that can only be ascertained in situ, will 

 exercise an influence upon the enormous reserves of 

 plant food contained in every soil. In any case the 

 chemical analysis of a single soil is of very little value 

 as a guide to the treatment of the soil in practice. 

 Exceptional deficiencies may be revealed, particularly 

 as regards calcium carbonate or sometimes as regards 

 phosphoric acid, but, as a rule, the figures obtained are 

 among the middle values which of themselves possess 

 no significance. What the analyst requires is a series 

 of analyses which characterise the soil type and indicate 

 the limits within which the natural variations fall. If, 

 further, the normal behaviour of the soil type towards 



