Lecture 1 



17 — 



Survey 



The California soils with which we experimented 

 were all slightly alkaline, according to general tests 

 with indicators. With the introduction of the hydrogen 



5i-Tetmheclron 



Pi- Octohedm 



/5tA, 



LMvMv 



6 = (OH) 

 o - Al 

 • - 5i 

 0= 





'MVi^^V 



o~ Al 

 •'6/ 



Textfigure 4. — Above: Two building units of crystal- 

 line structure of soil colloids. — Below : Showing proposed 

 crystalline structures of two general types of soil colloids, 

 kaolinite and montmorillonite. (From Kelley, Jenny and 

 Brown, 1936). 



electrode, the desirability of learning the effect of 

 hydrogen ion concentration on plant growth at spe- 

 cific intensities of acidity or alkalinity became obvious. 

 Was the alkaline reaction of the soils under study an 

 indispensable requisite for high crop yields? In seek- 

 ing an answer to this question plants were grown in 



