INFLUENCE OF ENVIRONMENTAL CONDITIONS 789 



alkali salts upon bacterial activities in the soil received special consid- 

 eration. 85 The chlorides are usually the most toxic salts, followed by 

 the nitrates, sulfates and carbonates. The nitrifying organisms are 

 more susceptible than the ammonia forming forms. There is a definite 

 antagonism between various ions. 86 However, the nature of the or- 

 ganism and the process used as an index of the antagonistic action 

 is of great importance. In suitable concentrations salts of arsenic, 87 

 copper, 88 lead, zinc, and iron, stimulate the activities of the nitrifying 

 and other bacteria. The action depends on the nature of the salt, 

 type of soil and nature of organism. Other investigators 89 recorded, 

 however, that As 2 3 in itself does not stimulate bacterial growth. 



The organisms that decompose proteins with the formation of am- 

 monia are apparently 90 more resistant to the action of salts than are 

 the higher plants. Nitrates are toxic to bacteria in definite concentra- 

 tions, the limits depending on the organism and the medium; 91 this 

 is true both of various autotrophic bacteria, independent of the ability 

 of the organisms to assimilate nitrate nitrogen. The activities of 

 the majority of heterotrophic organisms are favorably influenced by 

 small amounts of nitrate, due to the fact that it serves as a good 

 source of nitrogen. 



Influence of calcium oxide and carbonates of calcium and magnesium. 

 The influence of calcium oxide and calcium carbonate on the bacterial 

 numbers and their activities depends on the change produced in the 



86 Lipman, C. B. Toxic effects of alkali salts in soils on soil bacteria. Centrbl. 

 Bakt. II, 32: 5S-64. 1912; 33: 305-313, 647-655. 1912. Greaves, J. E. The 

 influence of salts on the bacterial activities of the soil. Soil Sci., 2: 443-480. 

 1916; Jour. Agr. Res., 16: 107-135. 1919; Kelley, W. P. Nitrification in semi- 

 arid soils. I. Jour. Agr. Res., 7: 417-437. 1916. 



86 Lipman, C. B. Bot. Gaz., 48: 106. 1909; Centrbl. Bakt. II, 41: 430^44. 

 1914; also Greaves, J. E. Soil Sci., 10: 77-102. 1920; Szucs, J. Experimentalle 

 Beitrage zu einer Theorie der antagonistischen Ionenwirkung. Jahrb. wiss. 

 Bot., 52: 85-142. 1912. 



87 Greaves, J. E., and Carter, E. G. Influence of sodium arsenite on micro- 

 flora of soil. Bot. Gaz., 77: 63-72. 1924; Centrbl. Bakt. II, 39: 542-560. 1913; 

 42: 244-254. 1914; Jour. Agr. Res., 6: 389^16. 1913. 



88 Lipman, C. B., and Burgess, P. S. Univ. Cal. Publ. Agr. Sci., 1: 127-139. 

 1914. 



89 Cobet, R., and van der Reis, V. Uber den Einflusz der arsenigen Siiure 

 auf das Bakterienwachstum. Biochem. Ztschr., 129: 73-88. 1922. 



90 Greaves, 1916-1919. 



91 Bottger, H. Uber die Giftwirkungen der Nitrate auf niedere Organismen. 

 Centrbl. Bakt. II, 54: 220-261. 1921. 



