274 ^OIL CONDITIONS AND PLANT GRO WTH 



Effect of Salts} — 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 CO2 production, ammonification, etc.^ 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 (i75<^) and by J, E. Greaves and his co-workers in 

 Utah (i 1 3). Typical results are given in Table LXXII. 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.^ 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 ; 

 (Na2)C03 and (Na)Cl) ^ as in the case of green plants (p. 79). 

 Salts of arsenic,^ copper,® 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 : '' potassium salts have acted well in 



^ For a summary of the extensive literature see J. E. Greaves, Soil Set., 

 1916, 2, 443 480. 



^ J. H. Barnes and Barkat Ali, Ag. jfourn. India, 1917, 12, 368. 



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



*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 Set., 1920, 10, 77-102. 



®J. E. Greaves, Scienee, 1917, p. 204. 



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

 127-139. 



'' 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. 



