78 THE SOIL SOLUTION 



tion occurs at the surface normally under humid conditions be- 

 cause the rainfall is sufficiently distributed throughout the year 

 to enable the cut-off water to carry back promptly into the lower 

 soil levels any excessive amount of soluble material, there to 

 start anew its slower ascent towards the surface. 



Calculations such as those here presented are at the best open 

 to many objections, and it is wise to avoid giving them too much 

 emphasis. So far as the available data justify any conclusion, 

 however, it appears that the rise of capillary water is entirely 

 capable of maintaining a sufficient supply of mineral nutrients for 

 crop requirements; and furthermore, it is obvious that the prob- 

 lem of the supply of mineral plant nutrients is dynamic and can- 

 not be successfully attacked by considerations which are essen- 

 tially static. 



