274 SOIL CONDITIONS AND PLANT GROWTH 



Effect of Salts. 1 Alkali salts adversely affect bacteria 

 somewhat as they do green plants : in India a sufficient de- 

 gree of similarity exists to allow the wheat-yielding power 

 of an alkali soil to be estimated from such bacterial 

 activities as CO 2 production, ammonification, etc. 2 The prob- 

 lem has been much investigated in the Western United 

 States where alkali salts are apt to cause trouble. System- 

 atic investigations have been made by C. B. Lipman in 

 California (175^) and by J. E. Greaves and his co-workers in 

 Utah (i 1 3). Typical results are given in Table LXXIL The 

 ammonifying organisms are usually stimulated by small con- 

 centrations of " alkali salts" but adversely affected by larger 

 ones, though they are less susceptible than wheat seedlings 

 The effect is not constant but varies with differences in soil 

 and conditions. 3 As a general rule chlorides are the most 

 toxic salts, while nitrates, sulphates, and carbonates are suc- 

 cessively less toxic ; it is suggested that the electronegative 

 ion plays the more important part (113). Nitrifying organ- 

 isms, however, are more susceptible than ammonia producers 

 and the effects are determined by the specific compound 

 rather than by one ion. There is also a well-marked anta- 

 gonism of ions (e.g. Ca and K ; Mg and Na ; K and Na ; 

 (Na 2 )CO 3 and (Na)Cl) 4 as in the case of green plants (p. 79). 

 Salts of arsenic, 5 copper, 6 lead, zinc, and iron appear to be 

 capable, in suitable concentration, of stimulating nitrifying 

 organisms but not ammonification. Nutritive salts have a 

 marked effect. Phosphates notably increase all types of bac- 

 terial activity in the soil : 7 potassium salts have acted well in 



1 For a summary of the extensive literature see J. E. Greaves, Soil Sci., 

 1916, 2, 443-480. 



a J. H. Barnes and Barkat Ali, Ag. Journ. India, 1917, 12, 368. 



3 W. P. Kelley, Journ. Agric. Research, 1916, 7, 417-437. 



4 C. B. Lipman, Bot. Gaz., 1909, 48, 106, and Centr. Bakt. Par., 1914, 41, 

 430-444 (with P. S. Burgess) ; see also J. E. Greaves, Soil Sci., 1920, 10, 77-102. 



5 J. E. Greaves, Science, 1917, p. 204. 



6 C. B. Lipman and P. S. Burgess, Univ. Cal. Pub. Agric. Sci., 1914, I, 

 127-139. 



7 E. B. Fred and E. B. Hart, Wisconsin Research Bull., 35, 1915 ; and 

 Centr. Bakt. Par., II., 1916, 45, 379 ; G. P. Koch, Journ. Biol. Chem., 1917, 31, 

 411 ; see also p. 203. 



