PROCEEDINGS OF SECTION K. 



665 



These observations seem to justify the conclusion that one of 

 the beneficial effects of superphosphate on wheat (and probably- 

 other agricultural plants) under semi-arid conditions is that it 

 causes the young plant to send its roots quickly into the subsoil, 

 thereby increasing not only its moisture absorbing capacity, but 

 also increasing very greatly the volume of soil from which it can 

 draw its moisture supply ; so that there is some justification for 

 the farmers who describe the effect of a dressing of from 40 to 60 

 lbs. of superphosphate per acre as equivalent to 2 or 3 inches of 

 rain. They further call attention to the great depth to which the 

 roots of agricultural plants under ordinary cultural conditions in 

 dry countries penetrate the subsoil in search of moisture, which is 

 one of the circumstances which makes the conservation of moisture 

 11' the subsoil by means of a well tilled fallow effective to the suc- 

 ceeding crop, and constitutes the root principle of " dry farming." 



Diagrammatic representation drawn to scale of the relative root and shoot 

 development in the case of the plots vi^hich showed the greatest contrast 

 due to the use of superphosphate. 



