[ 369 



XXX. 



SOME FACTOES AFFECTING THE HYDEOGEN ION CONCEN- 

 TEATION OF THE SOIL AND ITS EELATION TO PLANT 

 DISTEIBUTION. 



By W. E. G. ATKINS, O.B.E., Sc.D., F.I.C. 



(Communicated by Professor H. H. Dixon, sec, f.e.s.) 



[Eead Novemeek. 22, 1921. Published FErmuAKY 2, 1922.] 



Contents. 



Introduction, 



PAGE 



369 



concentration and 



(a) Hydrogen ion 



acidity, 



(i) Buffer action, ..... 

 («) The determination of hydrogen ion 



concentrations, ..... 



(d) Neutrality, 



(«) The hydrogen ion concentration of 



pure water, 



( f) The colorimetric method of deter- 

 mining hydrogen ion concentrations, . 



(g) Methods of determining soil reaction. 

 Agricultural application of studies on soil 



reaction, 



The relation of the ions of the soil solu- 

 tion to its hydrogen ion content, 



(ff) Calcium salts, .... 



(i) Magnesium salts 



(c) Action of gypsum on alkali lands. 



370 

 371 



371 

 373 



373 



375 

 376 



376 



378 

 378 

 380 

 382 



{d) Solubility of phosphates arid occur- 

 rence of sulphur acids, 



((') Solubility of iron salts, 



(/) Effect of manuring upon soil reaction, 



iff) Acid soils, 



(A) Aluminium salts (see under plant 

 distribution). 



The hydrogen ion concentration of heated 

 and unhealed soil, .... 



Nomenclature of soils with respect to 

 acidity and alkalinity. 



The relation of the hydrogen ion concen- 

 tration of soil to the geological forma- 

 tion originating it, . . . . 



The relation of the hydrogen ion concen- 

 tration of the soil to plant distribution. 



Garden cultivation of wild plants . 



The hydrogen ion concentration of natural 

 waters in relation to plant distribution, 



Summary, . . . 



383 

 384 

 385 

 380 



387 

 388 



388 



393 

 406 



407 

 412 



Introduction. 



It has long been customary to speak of certain soils as acid and of others as 

 alkaline, the terms being used as a rule only when these characteristics were 

 displayed to a marked degree so as to have obvious effects upon the vegetation. 

 Concerning the nature of soil acidity, a long-standing controvei'sy is 

 still in being, ami the views put forward have recently been summarized by 



SCIENT. PROC. R.D.S., VOL. XVI, KO. XXX. 



