CHAPTER VIII. 



SOIL ANALYSIS AND ITS INTERPRETATION. 



WHEN an agricultural chemist is asked to analyse a soil he is expected 

 to give some information about the crops to which it is best suited, and 

 the manures that must be applied ; he has, therefore, a much more 

 complex problem than the minerological or geological chemist who 

 simply has to report on the actual constituents he finds. It has been 

 shown in the last chapter that the vegetation relationships of soils are 

 not determined solely by the nature of the soil, but also by its posi- 

 tion, subsoil, climate, and other circumstances, so that it is manifestly 

 impossible for the chemist to make a satisfactory report on a sample 

 of soil on the basis of analytical data only. He cannot even give a 

 complete account of the soil itself, since he has no method of estimat- 

 ing the compound particles on which the water and air supply, the 

 temperature and the cultivation properties depend, but he can only get 

 at the ultimate particles out of which they are built. 



Soil analysis is, therefore, restricted to: (i) comparisons between 

 soils, showing which are fundamentally identical and in what respects 

 others differ; (2) the tracing of such correlations as exist between 

 the chemical and physical properties of the soils of a given area and 

 the crops and agricultural methods generally associated with them. In 

 order to carry out either of these satisfactorily it is necessary to make 

 a systematic soil survey, a task that is certainly laborious but by no 

 means impossible, since each agricultural chemist usually confines his 

 attention to a definite region a county or so and is not called upon 

 to deal with outside soils. 



In planning a soil survey it must be remembered that the basis of 

 the whole work is empirical : the agricultural and vegetation character- 

 istics have first to be ascertained by field trials, and then systematised 

 and amplified by aid of the laboratory data. It is necessary to begin, 

 therefore, by going over the whole region very carefully and dividing 

 it up in areas within which similar agricultural or vegetation character- 

 istics prevail. In g'eneral the areas differentiated in the geological 

 drift maps will be found identical with the vegetation areas, especially 



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