788 PRINCIPLES OF SOIL MICROBIOLOGY 



In addition to data recorded elsewhere (p. 733) concerning the in- 

 fluence of fertilization upon the activities of microorganisms , the 

 following results obtained by Given in Pennsylvania may be reported 

 here (table 90). 78 



Similar results were obtained by other investigators for other soils. 

 Phosphoric acid has a favorable influence upon the development of 

 Azotobacter. 79 The growth of this organism is in a certain way 

 proportional to the easily soluble phosphates in the soil. 80 It was 

 suggested 81 that the amount of nitrogen fixed in a phosphorus-free 

 mannite solution, to which a definite amount of soil is added, can be 

 used as an index of the available phosphorus in the soil. The addition 

 of available phosphates to the soil may bring about a large increase 

 in the number of soil bacteria and in the decomposition of organic 

 matter, as measured by the formation of ammonia and carbon dioxide ; 

 sulfates were found to exert only a limited effect. 82 The possibility 

 that the increased crop production resulting from the application of 

 phosphates to the soil is due, in part at least, to the stimulation of 

 bacterial activities was, therefore, suggested. The addition of NaN0 3 

 (NH^SO^ K 2 S0 4 , MgS0 4 to the soil has only a small stimulating effect 

 upon the numbers of bacteria. 83 



The continuous applications of large quantities of artificial ferti- 

 lizers may injure certain groups of bacteria, particularly the nitrate 

 forming organisms, which may be overcome by the nitrite formers. 84 

 Many bacteria and fungi can readily withstand high concentrations of 

 salts, varying from 5 to 15 per cent of sodium chloride, depending on the 

 nature of the salt and the type of the organism. The influence of 



78 Cited by Frear, W. Sour soils and liming. Pa. Dept. Agr. Bui. 261. 1915. 



79 Heinze, B. Uber die Stickstoffassimilation durch niedere Organismen. 

 Landw. Jahrb., 35: 889-910. 1906; Wilfarth, H., and Wimmer, G. "fiber den 

 Einfluss der Mineraldilngung auf die Stickstoffbindung durch niedere Organismen 

 im Boden. Landw. Vers. Sta., 67: 27-50. 1907. 



80 Lipman, J. G. Bacteriological indications of the mineral requirements 

 of soils. N. J. Agr. Exp. Sta. Ann. Rpt., 19: 177-187. 1906. 



81 Christensen, 1923 (p. 730); Stoklasa, 1925 (p. 621). 



82 Fred, E. B., and Hart, E. B. The effect of phosphates and sulfates on soil 

 bacteria. Wis. Agr. Exp. Sta. Res. Bui. 35. 1915; Centrbl. Bakt. II, 45: 379. 

 1916. 



88 Engberding, 1909 (p. 771). 



84 Aberson, Y. H. A contribution to the knowledge of the so-called physio- 

 logical acid and alkaline salts, and their importance for the explanation of the 

 sickness of the soil. Meddel. v. de Rijks Hoogere Hand Tuinen Boschborow- 

 school., 11: 1-93. 1916 (Physiol. Abstr., 1: 509. 1917). 



