Lecture 1 — 5 — Survey 



ing views of agriculturists and which aroused the 

 sharpest controversy. In their more extreme form at 

 least, these conclusions embodied the concept that the 

 liquid phase of the soil, the soil solution, and accord- 

 ing to then prevailing theory the immediate source of 

 the plant's inorganic nutrients, was a dilute solution 

 more or less similar in composition for most soils. 

 The reasoning was in part that soils are all extremely 

 heterogeneous, all containing relatively large amounts 

 of the principal soil minerals, and that a solution 

 saturated with respect to these minerals would be 

 present in the majority of soils. The effects of fer- 

 tilizers were ascribed often to factors other than that 

 of modifying the soil solution as a nutrient medium 

 for plants. Great stress was placed on the presumed 

 presence in infertile soils of toxic organic substances 

 in minute amounts. Fertilizers, it was thought, might 

 frequently act by overcoming in some way the effects 

 of these toxic substances. 



All this is now, of course, only of historical interest. 

 Certain fallacies in the view I have outlined have long 

 been apparent. Nevertheless, these early discussions 

 had valuable consequences. For too long had the 

 thinking of students of plant nutrition been influenced 

 by the doctrine of statics as enunciated by Liebig — 

 that the fertility of a soil rose and fell in exact pro- 

 portion to the mineral nutrients withdrawn from or 

 added to the soil. The discussions to which I refer 

 argued strongly for a dynamic interpretation of the 

 soil system and this was sound despite erroneous teach- 

 ings as to the particular nature of the system. 



This, then, was the general background of our own 

 initial researches in plant nutrition, inaugurated under 

 the direction of Professor J. S. Burd, associated with 

 G. R. Stewart and others. Much had been written 

 about the soil solution and controversy had not ceased. 

 It was apparent that experimental evidence was most 

 inadequate. Generally, chemical analyses had been 

 made on field samples of soil under no adequate con>-'j* ■ m 7** 



'^ II IBR AR 



