THE SOIL AND THE PLANT 



A REVIEW OF SOME RECENT AMERICAN 



HYPOTHESES 



By EDWARD J. RUSSELL, D.Sc. (Lond.) 

 Goldsmith Company's Soil Chemist, Rothamsted Experimental Station 



In order that the reader may be in a position to appreciate 

 the exact force of the hypotheses to be discussed here and 

 to understand the precise bearing of the points at issue in 

 the controversies to which they have given rise, it is desirable 

 at the outset to state briefly the salient features of the relation- 

 ships between soil and plant. 



Various conditions have to be fulfilled in order that a plant 

 may make satisfactory growth : there must be sufficient food, 

 water, air, warmth and light, also there must be an absence 

 of harmful and inhibiting factors. Further, if the plant is to 

 be grown economically and without undue risk of loss, the 

 soil must provide a sufficiently firm anchorage ground, so 

 that the plant can stand up well and not suffer too much from 

 wind. For our present purpose, we may dismiss the action 

 of light as being unconnected with the soil and group the 

 remaining requirements in two main classes : food supply and 

 certain inhibiting factors, which are largely connected with 

 the chemical properties of the soil, form the one ; the water, 

 air, temperature and root-hold factors, which are more 

 closely related to its physical properties, the second. The 

 distinction is further convenient in that it also indicates the 

 lines of cleavage in the discussions that have centred round 

 the hypotheses now under discussion. 



All these factors are of equal importance. A deficiency of 

 any one of them sets a limit to the effectiveness of the others 

 and consequently to the crop growth. Thus, no matter how 

 much food may be supplied, the plant cannot make a corre- 

 sponding growth if the water supply be insufficient or the tem- 

 perature too low. It is therefore fatal to our subject to take 



i35 



